Merge branch 'master' into playlist-max-room-attempts

README.md

@@ -5,7 +5,7 @@
 # osu!
 
 [![Build status](https://ci.appveyor.com/api/projects/status/u2p01nx7l6og8buh?svg=true)](https://ci.appveyor.com/project/peppy/osu)
-[![GitHub release](https://img.shields.io/github/release/ppy/osu.svg)]()
+[![GitHub release](https://img.shields.io/github/release/ppy/osu.svg)](https://github.com/ppy/osu/releases/latest)
 [![CodeFactor](https://www.codefactor.io/repository/github/ppy/osu/badge)](https://www.codefactor.io/repository/github/ppy/osu)
 [![dev chat](https://discordapp.com/api/guilds/188630481301012481/widget.png?style=shield)](https://discord.gg/ppy)
 

osu.Game.Rulesets.Catch/Skinning/Default/BorderPiece.cs

@@ -29,4 +29,3 @@ namespace osu.Game.Rulesets.Catch.Skinning.Default
         }
     }
 }
-

osu.Game.Rulesets.Catch/Skinning/Default/HyperBorderPiece.cs

@@ -19,4 +19,3 @@ namespace osu.Game.Rulesets.Catch.Skinning.Default
         }
     }
 }
-

osu.Game.Rulesets.Mania.Tests/Mods/TestSceneManiaModConstantSpeed.cs

@@ -0,0 +1,31 @@
+// Copyright (c) ppy Pty Ltd <contact@ppy.sh>. Licensed under the MIT Licence.
+// See the LICENCE file in the repository root for full licence text.
+
+using System.Linq;
+using NUnit.Framework;
+using osu.Framework.Allocation;
+using osu.Framework.Testing;
+using osu.Game.Rulesets.Mania.Mods;
+using osu.Game.Rulesets.Mania.Objects.Drawables;
+using osu.Game.Rulesets.UI.Scrolling;
+using osu.Game.Rulesets.UI.Scrolling.Algorithms;
+using osu.Game.Tests.Visual;
+
+namespace osu.Game.Rulesets.Mania.Tests.Mods
+{
+    public class TestSceneManiaModConstantSpeed : ModTestScene
+    {
+        protected override Ruleset CreatePlayerRuleset() => new ManiaRuleset();
+
+        [Test]
+        public void TestConstantScroll() => CreateModTest(new ModTestData
+        {
+            Mod = new ManiaModConstantSpeed(),
+            PassCondition = () =>
+            {
+                var hitObject = Player.ChildrenOfType<DrawableManiaHitObject>().FirstOrDefault();
+                return hitObject?.Dependencies.Get<IScrollingInfo>().Algorithm is ConstantScrollAlgorithm;
+            }
+        });
+    }
+}

osu.Game.Rulesets.Mania/ManiaRuleset.cs

@@ -238,6 +238,7 @@ namespace osu.Game.Rulesets.Mania
                         new ManiaModMirror(),
                         new ManiaModDifficultyAdjust(),
                         new ManiaModInvert(),
+                        new ManiaModConstantSpeed()
                     };
 
                 case ModType.Automation:

osu.Game.Rulesets.Mania/Mods/ManiaModConstantSpeed.cs

@@ -0,0 +1,35 @@
+// Copyright (c) ppy Pty Ltd <contact@ppy.sh>. Licensed under the MIT Licence.
+// See the LICENCE file in the repository root for full licence text.
+
+using osu.Framework.Graphics.Sprites;
+using osu.Game.Configuration;
+using osu.Game.Rulesets.Mania.Objects;
+using osu.Game.Rulesets.Mania.UI;
+using osu.Game.Rulesets.Mods;
+using osu.Game.Rulesets.UI;
+
+namespace osu.Game.Rulesets.Mania.Mods
+{
+    public class ManiaModConstantSpeed : Mod, IApplicableToDrawableRuleset<ManiaHitObject>
+    {
+        public override string Name => "Constant Speed";
+
+        public override string Acronym => "CS";
+
+        public override double ScoreMultiplier => 1;
+
+        public override string Description => "No more tricky speed changes!";
+
+        public override IconUsage? Icon => FontAwesome.Solid.Equals;
+
+        public override ModType Type => ModType.Conversion;
+
+        public override bool Ranked => false;
+
+        public void ApplyToDrawableRuleset(DrawableRuleset<ManiaHitObject> drawableRuleset)
+        {
+            var maniaRuleset = (DrawableManiaRuleset)drawableRuleset;
+            maniaRuleset.ScrollMethod = ScrollVisualisationMethod.Constant;
+        }
+    }
+}

osu.Game.Rulesets.Mania/UI/DrawableManiaRuleset.cs

@@ -1,6 +1,7 @@
 // Copyright (c) ppy Pty Ltd <contact@ppy.sh>. Licensed under the MIT Licence.
 // See the LICENCE file in the repository root for full licence text.
 
+using System;
 using System.Collections.Generic;
 using System.Linq;
 using osu.Framework.Allocation;
@@ -11,6 +12,7 @@ using osu.Framework.Graphics;
 using osu.Framework.Input;
 using osu.Game.Beatmaps;
 using osu.Game.Beatmaps.ControlPoints;
+using osu.Game.Configuration;
 using osu.Game.Input.Handlers;
 using osu.Game.Replays;
 using osu.Game.Rulesets.Mania.Beatmaps;
@@ -49,6 +51,22 @@ namespace osu.Game.Rulesets.Mania.UI
 
         protected new ManiaRulesetConfigManager Config => (ManiaRulesetConfigManager)base.Config;
 
+        public ScrollVisualisationMethod ScrollMethod
+        {
+            get => scrollMethod;
+            set
+            {
+                if (IsLoaded)
+                    throw new InvalidOperationException($"Can't alter {nameof(ScrollMethod)} after ruleset is already loaded");
+
+                scrollMethod = value;
+            }
+        }
+
+        private ScrollVisualisationMethod scrollMethod = ScrollVisualisationMethod.Sequential;
+
+        protected override ScrollVisualisationMethod VisualisationMethod => scrollMethod;
+
         private readonly Bindable<ManiaScrollingDirection> configDirection = new Bindable<ManiaScrollingDirection>();
         private readonly Bindable<double> configTimeRange = new BindableDouble();
 

osu.Game.Tests.Android/osu.Game.Tests.Android.csproj

@@ -69,5 +69,9 @@
       <Name>osu.Game</Name>
     </ProjectReference>
   </ItemGroup>
+  <ItemGroup Label="Package References">
+    <PackageReference Include="DeepEqual" Version="2.0.0" />
+    <PackageReference Include="Moq" Version="4.16.0" />
+  </ItemGroup>
   <Import Project="$(MSBuildExtensionsPath)\Xamarin\Android\Xamarin.Android.CSharp.targets" />
 </Project>

osu.Game.Tests.iOS/osu.Game.Tests.iOS.csproj

@@ -45,6 +45,7 @@
   </ItemGroup>
   <ItemGroup Label="Package References">
     <PackageReference Include="DeepEqual" Version="2.0.0" />
+    <PackageReference Include="Moq" Version="4.16.0" />
   </ItemGroup>
   <Import Project="$(MSBuildExtensionsPath)\Xamarin\iOS\Xamarin.iOS.CSharp.targets" />
 </Project>

osu.Game.Tests/Mods/ModUtilsTest.cs

@@ -0,0 +1,160 @@
+// Copyright (c) ppy Pty Ltd <contact@ppy.sh>. Licensed under the MIT Licence.
+// See the LICENCE file in the repository root for full licence text.
+
+using System;
+using System.Linq;
+using Moq;
+using NUnit.Framework;
+using osu.Game.Rulesets.Mods;
+using osu.Game.Rulesets.Osu.Mods;
+using osu.Game.Utils;
+
+namespace osu.Game.Tests.Mods
+{
+    [TestFixture]
+    public class ModUtilsTest
+    {
+        [Test]
+        public void TestModIsCompatibleByItself()
+        {
+            var mod = new Mock<CustomMod1>();
+            Assert.That(ModUtils.CheckCompatibleSet(new[] { mod.Object }));
+        }
+
+        [Test]
+        public void TestIncompatibleThroughTopLevel()
+        {
+            var mod1 = new Mock<CustomMod1>();
+            var mod2 = new Mock<CustomMod2>();
+
+            mod1.Setup(m => m.IncompatibleMods).Returns(new[] { mod2.Object.GetType() });
+
+            // Test both orderings.
+            Assert.That(ModUtils.CheckCompatibleSet(new Mod[] { mod1.Object, mod2.Object }), Is.False);
+            Assert.That(ModUtils.CheckCompatibleSet(new Mod[] { mod2.Object, mod1.Object }), Is.False);
+        }
+
+        [Test]
+        public void TestMultiModIncompatibleWithTopLevel()
+        {
+            var mod1 = new Mock<CustomMod1>();
+
+            // The nested mod.
+            var mod2 = new Mock<CustomMod2>();
+            mod2.Setup(m => m.IncompatibleMods).Returns(new[] { mod1.Object.GetType() });
+
+            var multiMod = new MultiMod(new MultiMod(mod2.Object));
+
+            // Test both orderings.
+            Assert.That(ModUtils.CheckCompatibleSet(new Mod[] { multiMod, mod1.Object }), Is.False);
+            Assert.That(ModUtils.CheckCompatibleSet(new Mod[] { mod1.Object, multiMod }), Is.False);
+        }
+
+        [Test]
+        public void TestTopLevelIncompatibleWithMultiMod()
+        {
+            // The nested mod.
+            var mod1 = new Mock<CustomMod1>();
+            var multiMod = new MultiMod(new MultiMod(mod1.Object));
+
+            var mod2 = new Mock<CustomMod2>();
+            mod2.Setup(m => m.IncompatibleMods).Returns(new[] { typeof(CustomMod1) });
+
+            // Test both orderings.
+            Assert.That(ModUtils.CheckCompatibleSet(new Mod[] { multiMod, mod2.Object }), Is.False);
+            Assert.That(ModUtils.CheckCompatibleSet(new Mod[] { mod2.Object, multiMod }), Is.False);
+        }
+
+        [Test]
+        public void TestCompatibleMods()
+        {
+            var mod1 = new Mock<CustomMod1>();
+            var mod2 = new Mock<CustomMod2>();
+
+            // Test both orderings.
+            Assert.That(ModUtils.CheckCompatibleSet(new Mod[] { mod1.Object, mod2.Object }), Is.True);
+            Assert.That(ModUtils.CheckCompatibleSet(new Mod[] { mod2.Object, mod1.Object }), Is.True);
+        }
+
+        [Test]
+        public void TestIncompatibleThroughBaseType()
+        {
+            var mod1 = new Mock<CustomMod1>();
+            var mod2 = new Mock<CustomMod2>();
+            mod2.Setup(m => m.IncompatibleMods).Returns(new[] { typeof(Mod) });
+
+            // Test both orderings.
+            Assert.That(ModUtils.CheckCompatibleSet(new Mod[] { mod1.Object, mod2.Object }), Is.False);
+            Assert.That(ModUtils.CheckCompatibleSet(new Mod[] { mod2.Object, mod1.Object }), Is.False);
+        }
+
+        [Test]
+        public void TestAllowedThroughMostDerivedType()
+        {
+            var mod = new Mock<CustomMod1>();
+            Assert.That(ModUtils.CheckAllowed(new[] { mod.Object }, new[] { mod.Object.GetType() }));
+        }
+
+        [Test]
+        public void TestNotAllowedThroughBaseType()
+        {
+            var mod = new Mock<CustomMod1>();
+            Assert.That(ModUtils.CheckAllowed(new[] { mod.Object }, new[] { typeof(Mod) }), Is.False);
+        }
+
+        private static readonly object[] invalid_mod_test_scenarios =
+        {
+            // incompatible pair.
+            new object[]
+            {
+                new Mod[] { new OsuModDoubleTime(), new OsuModHalfTime() },
+                new[] { typeof(OsuModDoubleTime), typeof(OsuModHalfTime) }
+            },
+            // incompatible pair with derived class.
+            new object[]
+            {
+                new Mod[] { new OsuModNightcore(), new OsuModHalfTime() },
+                new[] { typeof(OsuModNightcore), typeof(OsuModHalfTime) }
+            },
+            // system mod.
+            new object[]
+            {
+                new Mod[] { new OsuModDoubleTime(), new OsuModTouchDevice() },
+                new[] { typeof(OsuModTouchDevice) }
+            },
+            // multi mod.
+            new object[]
+            {
+                new Mod[] { new MultiMod(new OsuModHalfTime()), new OsuModHalfTime() },
+                new[] { typeof(MultiMod) }
+            },
+            // valid pair.
+            new object[]
+            {
+                new Mod[] { new OsuModDoubleTime(), new OsuModHardRock() },
+                null
+            }
+        };
+
+        [TestCaseSource(nameof(invalid_mod_test_scenarios))]
+        public void TestInvalidModScenarios(Mod[] inputMods, Type[] expectedInvalid)
+        {
+            bool isValid = ModUtils.CheckValidForGameplay(inputMods, out var invalid);
+
+            Assert.That(isValid, Is.EqualTo(expectedInvalid == null));
+
+            if (isValid)
+                Assert.IsNull(invalid);
+            else
+                Assert.That(invalid?.Select(t => t.GetType()), Is.EquivalentTo(expectedInvalid));
+        }
+
+        public abstract class CustomMod1 : Mod
+        {
+        }
+
+        public abstract class CustomMod2 : Mod
+        {
+        }
+    }
+}

osu.Game.Tests/NonVisual/OngoingOperationTrackerTest.cs

@@ -3,8 +3,12 @@
 
 using System;
 using NUnit.Framework;
+using osu.Framework.Allocation;
 using osu.Framework.Bindables;
+using osu.Framework.Graphics;
+using osu.Framework.Screens;
 using osu.Framework.Testing;
+using osu.Game.Screens;
 using osu.Game.Screens.OnlinePlay;
 using osu.Game.Tests.Visual;
 
@@ -58,5 +62,45 @@ namespace osu.Game.Tests.NonVisual
             AddStep("end operation", () => operation.Dispose());
             AddAssert("operation is ended", () => !operationInProgress.Value);
         }
+
+        [Test]
+        public void TestOperationDisposalAfterScreenExit()
+        {
+            TestScreenWithTracker screen = null;
+            OsuScreenStack stack;
+            IDisposable operation = null;
+
+            AddStep("create screen with tracker", () =>
+            {
+                Child = stack = new OsuScreenStack
+                {
+                    RelativeSizeAxes = Axes.Both
+                };
+
+                stack.Push(screen = new TestScreenWithTracker());
+            });
+            AddUntilStep("wait for loaded", () => screen.IsLoaded);
+
+            AddStep("begin operation", () => operation = screen.OngoingOperationTracker.BeginOperation());
+            AddAssert("operation in progress", () => screen.OngoingOperationTracker.InProgress.Value);
+
+            AddStep("dispose after screen exit", () =>
+            {
+                screen.Exit();
+                operation.Dispose();
+            });
+            AddAssert("operation ended", () => !screen.OngoingOperationTracker.InProgress.Value);
+        }
+
+        private class TestScreenWithTracker : OsuScreen
+        {
+            public OngoingOperationTracker OngoingOperationTracker { get; private set; }
+
+            [BackgroundDependencyLoader]
+            private void load()
+            {
+                InternalChild = OngoingOperationTracker = new OngoingOperationTracker();
+            }
+        }
     }
 }

osu.Game.Tests/Online/TestAPIModJsonSerialization.cs

@@ -16,7 +16,7 @@ using osu.Game.Rulesets.UI;
 namespace osu.Game.Tests.Online
 {
     [TestFixture]
-    public class TestAPIModSerialization
+    public class TestAPIModJsonSerialization
     {
         [Test]
         public void TestAcronymIsPreserved()

osu.Game.Tests/Online/TestAPIModMessagePackSerialization.cs

@@ -0,0 +1,139 @@
+// Copyright (c) ppy Pty Ltd <contact@ppy.sh>. Licensed under the MIT Licence.
+// See the LICENCE file in the repository root for full licence text.
+
+using System.Collections.Generic;
+using MessagePack;
+using NUnit.Framework;
+using osu.Framework.Bindables;
+using osu.Game.Beatmaps;
+using osu.Game.Configuration;
+using osu.Game.Online.API;
+using osu.Game.Rulesets;
+using osu.Game.Rulesets.Difficulty;
+using osu.Game.Rulesets.Mods;
+using osu.Game.Rulesets.UI;
+
+namespace osu.Game.Tests.Online
+{
+    [TestFixture]
+    public class TestAPIModMessagePackSerialization
+    {
+        [Test]
+        public void TestAcronymIsPreserved()
+        {
+            var apiMod = new APIMod(new TestMod());
+
+            var deserialized = MessagePackSerializer.Deserialize<APIMod>(MessagePackSerializer.Serialize(apiMod));
+
+            Assert.That(deserialized.Acronym, Is.EqualTo(apiMod.Acronym));
+        }
+
+        [Test]
+        public void TestRawSettingIsPreserved()
+        {
+            var apiMod = new APIMod(new TestMod { TestSetting = { Value = 2 } });
+
+            var deserialized = MessagePackSerializer.Deserialize<APIMod>(MessagePackSerializer.Serialize(apiMod));
+
+            Assert.That(deserialized.Settings, Contains.Key("test_setting").With.ContainValue(2.0));
+        }
+
+        [Test]
+        public void TestConvertedModHasCorrectSetting()
+        {
+            var apiMod = new APIMod(new TestMod { TestSetting = { Value = 2 } });
+
+            var deserialized = MessagePackSerializer.Deserialize<APIMod>(MessagePackSerializer.Serialize(apiMod));
+            var converted = (TestMod)deserialized.ToMod(new TestRuleset());
+
+            Assert.That(converted.TestSetting.Value, Is.EqualTo(2));
+        }
+
+        [Test]
+        public void TestDeserialiseTimeRampMod()
+        {
+            // Create the mod with values different from default.
+            var apiMod = new APIMod(new TestModTimeRamp
+            {
+                AdjustPitch = { Value = false },
+                InitialRate = { Value = 1.25 },
+                FinalRate = { Value = 0.25 }
+            });
+
+            var deserialised = MessagePackSerializer.Deserialize<APIMod>(MessagePackSerializer.Serialize(apiMod));
+            var converted = (TestModTimeRamp)deserialised.ToMod(new TestRuleset());
+
+            Assert.That(converted.AdjustPitch.Value, Is.EqualTo(false));
+            Assert.That(converted.InitialRate.Value, Is.EqualTo(1.25));
+            Assert.That(converted.FinalRate.Value, Is.EqualTo(0.25));
+        }
+
+        private class TestRuleset : Ruleset
+        {
+            public override IEnumerable<Mod> GetModsFor(ModType type) => new Mod[]
+            {
+                new TestMod(),
+                new TestModTimeRamp(),
+            };
+
+            public override DrawableRuleset CreateDrawableRulesetWith(IBeatmap beatmap, IReadOnlyList<Mod> mods = null) => throw new System.NotImplementedException();
+
+            public override IBeatmapConverter CreateBeatmapConverter(IBeatmap beatmap) => throw new System.NotImplementedException();
+
+            public override DifficultyCalculator CreateDifficultyCalculator(WorkingBeatmap beatmap) => throw new System.NotImplementedException();
+
+            public override string Description { get; } = string.Empty;
+            public override string ShortName { get; } = string.Empty;
+        }
+
+        private class TestMod : Mod
+        {
+            public override string Name => "Test Mod";
+            public override string Acronym => "TM";
+            public override double ScoreMultiplier => 1;
+
+            [SettingSource("Test")]
+            public BindableNumber<double> TestSetting { get; } = new BindableDouble
+            {
+                MinValue = 0,
+                MaxValue = 10,
+                Default = 5,
+                Precision = 0.01,
+            };
+        }
+
+        private class TestModTimeRamp : ModTimeRamp
+        {
+            public override string Name => "Test Mod";
+            public override string Acronym => "TMTR";
+            public override double ScoreMultiplier => 1;
+
+            [SettingSource("Initial rate", "The starting speed of the track")]
+            public override BindableNumber<double> InitialRate { get; } = new BindableDouble
+            {
+                MinValue = 1,
+                MaxValue = 2,
+                Default = 1.5,
+                Value = 1.5,
+                Precision = 0.01,
+            };
+
+            [SettingSource("Final rate", "The speed increase to ramp towards")]
+            public override BindableNumber<double> FinalRate { get; } = new BindableDouble
+            {
+                MinValue = 0,
+                MaxValue = 1,
+                Default = 0.5,
+                Value = 0.5,
+                Precision = 0.01,
+            };
+
+            [SettingSource("Adjust pitch", "Should pitch be adjusted with speed")]
+            public override BindableBool AdjustPitch { get; } = new BindableBool
+            {
+                Default = true,
+                Value = true
+            };
+        }
+    }
+}

osu.Game.Tests/Online/TestSceneOnlinePlayBeatmapAvailabilityTracker.cs

@@ -0,0 +1,188 @@
+// Copyright (c) ppy Pty Ltd <contact@ppy.sh>. Licensed under the MIT Licence.
+// See the LICENCE file in the repository root for full licence text.
+
+using System;
+using System.Collections.Generic;
+using System.IO;
+using System.Threading;
+using System.Threading.Tasks;
+using JetBrains.Annotations;
+using NUnit.Framework;
+using osu.Framework.Allocation;
+using osu.Framework.Audio;
+using osu.Framework.Bindables;
+using osu.Framework.Extensions;
+using osu.Framework.Platform;
+using osu.Framework.Testing;
+using osu.Game.Beatmaps;
+using osu.Game.Beatmaps.Formats;
+using osu.Game.Database;
+using osu.Game.IO;
+using osu.Game.IO.Archives;
+using osu.Game.Online.API;
+using osu.Game.Online.Rooms;
+using osu.Game.Rulesets;
+using osu.Game.Tests.Resources;
+using osu.Game.Tests.Visual;
+
+namespace osu.Game.Tests.Online
+{
+    [HeadlessTest]
+    public class TestSceneOnlinePlayBeatmapAvailabilityTracker : OsuTestScene
+    {
+        private RulesetStore rulesets;
+        private TestBeatmapManager beatmaps;
+
+        private string testBeatmapFile;
+        private BeatmapInfo testBeatmapInfo;
+        private BeatmapSetInfo testBeatmapSet;
+
+        private readonly Bindable<PlaylistItem> selectedItem = new Bindable<PlaylistItem>();
+        private OnlinePlayBeatmapAvailablilityTracker availablilityTracker;
+
+        [BackgroundDependencyLoader]
+        private void load(AudioManager audio, GameHost host)
+        {
+            Dependencies.Cache(rulesets = new RulesetStore(ContextFactory));
+            Dependencies.CacheAs<BeatmapManager>(beatmaps = new TestBeatmapManager(LocalStorage, ContextFactory, rulesets, API, audio, host, Beatmap.Default));
+        }
+
+        [SetUp]
+        public void SetUp() => Schedule(() =>
+        {
+            beatmaps.AllowImport = new TaskCompletionSource<bool>();
+
+            testBeatmapFile = TestResources.GetTestBeatmapForImport();
+
+            testBeatmapInfo = getTestBeatmapInfo(testBeatmapFile);
+            testBeatmapSet = testBeatmapInfo.BeatmapSet;
+
+            var existing = beatmaps.QueryBeatmapSet(s => s.OnlineBeatmapSetID == testBeatmapSet.OnlineBeatmapSetID);
+            if (existing != null)
+                beatmaps.Delete(existing);
+
+            selectedItem.Value = new PlaylistItem
+            {
+                Beatmap = { Value = testBeatmapInfo },
+                Ruleset = { Value = testBeatmapInfo.Ruleset },
+            };
+
+            Child = availablilityTracker = new OnlinePlayBeatmapAvailablilityTracker
+            {
+                SelectedItem = { BindTarget = selectedItem, }
+            };
+        });
+
+        [Test]
+        public void TestBeatmapDownloadingFlow()
+        {
+            AddAssert("ensure beatmap unavailable", () => !beatmaps.IsAvailableLocally(testBeatmapSet));
+            addAvailabilityCheckStep("state not downloaded", BeatmapAvailability.NotDownloaded);
+
+            AddStep("start downloading", () => beatmaps.Download(testBeatmapSet));
+            addAvailabilityCheckStep("state downloading 0%", () => BeatmapAvailability.Downloading(0.0f));
+
+            AddStep("set progress 40%", () => ((TestDownloadRequest)beatmaps.GetExistingDownload(testBeatmapSet)).SetProgress(0.4f));
+            addAvailabilityCheckStep("state downloading 40%", () => BeatmapAvailability.Downloading(0.4f));
+
+            AddStep("finish download", () => ((TestDownloadRequest)beatmaps.GetExistingDownload(testBeatmapSet)).TriggerSuccess(testBeatmapFile));
+            addAvailabilityCheckStep("state importing", BeatmapAvailability.Importing);
+
+            AddStep("allow importing", () => beatmaps.AllowImport.SetResult(true));
+            AddUntilStep("wait for import", () => beatmaps.CurrentImportTask?.IsCompleted == true);
+            addAvailabilityCheckStep("state locally available", BeatmapAvailability.LocallyAvailable);
+        }
+
+        [Test]
+        public void TestTrackerRespectsSoftDeleting()
+        {
+            AddStep("allow importing", () => beatmaps.AllowImport.SetResult(true));
+            AddStep("import beatmap", () => beatmaps.Import(testBeatmapFile).Wait());
+            addAvailabilityCheckStep("state locally available", BeatmapAvailability.LocallyAvailable);
+
+            AddStep("delete beatmap", () => beatmaps.Delete(beatmaps.QueryBeatmapSet(b => b.OnlineBeatmapSetID == testBeatmapSet.OnlineBeatmapSetID)));
+            addAvailabilityCheckStep("state not downloaded", BeatmapAvailability.NotDownloaded);
+
+            AddStep("undelete beatmap", () => beatmaps.Undelete(beatmaps.QueryBeatmapSet(b => b.OnlineBeatmapSetID == testBeatmapSet.OnlineBeatmapSetID)));
+            addAvailabilityCheckStep("state locally available", BeatmapAvailability.LocallyAvailable);
+        }
+
+        [Test]
+        public void TestTrackerRespectsChecksum()
+        {
+            AddStep("allow importing", () => beatmaps.AllowImport.SetResult(true));
+
+            AddStep("import altered beatmap", () =>
+            {
+                beatmaps.Import(TestResources.GetTestBeatmapForImport(true)).Wait();
+            });
+            addAvailabilityCheckStep("state still not downloaded", BeatmapAvailability.NotDownloaded);
+
+            AddStep("recreate tracker", () => Child = availablilityTracker = new OnlinePlayBeatmapAvailablilityTracker
+            {
+                SelectedItem = { BindTarget = selectedItem }
+            });
+            addAvailabilityCheckStep("state not downloaded as well", BeatmapAvailability.NotDownloaded);
+        }
+
+        private void addAvailabilityCheckStep(string description, Func<BeatmapAvailability> expected)
+        {
+            AddAssert(description, () => availablilityTracker.Availability.Value.Equals(expected.Invoke()));
+        }
+
+        private static BeatmapInfo getTestBeatmapInfo(string archiveFile)
+        {
+            BeatmapInfo info;
+
+            using (var archive = new ZipArchiveReader(File.OpenRead(archiveFile)))
+            using (var stream = archive.GetStream("Soleily - Renatus (Gamu) [Insane].osu"))
+            using (var reader = new LineBufferedReader(stream))
+            {
+                var decoder = Decoder.GetDecoder<Beatmap>(reader);
+                var beatmap = decoder.Decode(reader);
+
+                info = beatmap.BeatmapInfo;
+                info.BeatmapSet.Beatmaps = new List<BeatmapInfo> { info };
+                info.BeatmapSet.Metadata = info.Metadata;
+                info.MD5Hash = stream.ComputeMD5Hash();
+                info.Hash = stream.ComputeSHA2Hash();
+            }
+
+            return info;
+        }
+
+        private class TestBeatmapManager : BeatmapManager
+        {
+            public TaskCompletionSource<bool> AllowImport = new TaskCompletionSource<bool>();
+
+            public Task<BeatmapSetInfo> CurrentImportTask { get; private set; }
+
+            protected override ArchiveDownloadRequest<BeatmapSetInfo> CreateDownloadRequest(BeatmapSetInfo set, bool minimiseDownloadSize)
+                => new TestDownloadRequest(set);
+
+            public TestBeatmapManager(Storage storage, IDatabaseContextFactory contextFactory, RulesetStore rulesets, IAPIProvider api, [NotNull] AudioManager audioManager, GameHost host = null, WorkingBeatmap defaultBeatmap = null, bool performOnlineLookups = false)
+                : base(storage, contextFactory, rulesets, api, audioManager, host, defaultBeatmap, performOnlineLookups)
+            {
+            }
+
+            public override async Task<BeatmapSetInfo> Import(BeatmapSetInfo item, ArchiveReader archive = null, CancellationToken cancellationToken = default)
+            {
+                await AllowImport.Task;
+                return await (CurrentImportTask = base.Import(item, archive, cancellationToken));
+            }
+        }
+
+        private class TestDownloadRequest : ArchiveDownloadRequest<BeatmapSetInfo>
+        {
+            public new void SetProgress(float progress) => base.SetProgress(progress);
+            public new void TriggerSuccess(string filename) => base.TriggerSuccess(filename);
+
+            public TestDownloadRequest(BeatmapSetInfo model)
+                : base(model)
+            {
+            }
+
+            protected override string Target => null;
+        }
+    }
+}

osu.Game.Tests/Visual/Multiplayer/TestSceneDrawableRoomPlaylist.cs

@@ -11,8 +11,8 @@ using osu.Framework.Graphics.Containers;
 using osu.Framework.Platform;
 using osu.Framework.Testing;
 using osu.Game.Beatmaps;
+using osu.Game.Beatmaps.Drawables;
 using osu.Game.Graphics.Containers;
-using osu.Game.Graphics.UserInterface;
 using osu.Game.Online.Rooms;
 using osu.Game.Overlays;
 using osu.Game.Rulesets;
@@ -20,6 +20,7 @@ using osu.Game.Rulesets.Osu;
 using osu.Game.Rulesets.Osu.Mods;
 using osu.Game.Screens.OnlinePlay;
 using osu.Game.Tests.Beatmaps;
+using osu.Game.Users;
 using osuTK;
 using osuTK.Input;
 
@@ -241,7 +242,7 @@ namespace osu.Game.Tests.Visual.Multiplayer
         }
 
         private void moveToItem(int index, Vector2? offset = null)
-            => AddStep($"move mouse to item {index}", () => InputManager.MoveMouseTo(playlist.ChildrenOfType<OsuRearrangeableListItem<PlaylistItem>>().ElementAt(index), offset));
+            => AddStep($"move mouse to item {index}", () => InputManager.MoveMouseTo(playlist.ChildrenOfType<DifficultyIcon>().ElementAt(index), offset));
 
         private void moveToDragger(int index, Vector2? offset = null) => AddStep($"move mouse to dragger {index}", () =>
         {
@@ -252,7 +253,7 @@ namespace osu.Game.Tests.Visual.Multiplayer
         private void moveToDeleteButton(int index, Vector2? offset = null) => AddStep($"move mouse to delete button {index}", () =>
         {
             var item = playlist.ChildrenOfType<OsuRearrangeableListItem<PlaylistItem>>().ElementAt(index);
-            InputManager.MoveMouseTo(item.ChildrenOfType<IconButton>().ElementAt(0), offset);
+            InputManager.MoveMouseTo(item.ChildrenOfType<DrawableRoomPlaylistItem.PlaylistRemoveButton>().ElementAt(0), offset);
         });
 
         private void assertHandleVisibility(int index, bool visible)
@@ -260,7 +261,7 @@ namespace osu.Game.Tests.Visual.Multiplayer
                 () => (playlist.ChildrenOfType<OsuRearrangeableListItem<PlaylistItem>.PlaylistItemHandle>().ElementAt(index).Alpha > 0) == visible);
 
         private void assertDeleteButtonVisibility(int index, bool visible)
-            => AddAssert($"delete button {index} {(visible ? "is" : "is not")} visible", () => (playlist.ChildrenOfType<IconButton>().ElementAt(2 + index * 2).Alpha > 0) == visible);
+            => AddAssert($"delete button {index} {(visible ? "is" : "is not")} visible", () => (playlist.ChildrenOfType<DrawableRoomPlaylistItem.PlaylistRemoveButton>().ElementAt(2 + index * 2).Alpha > 0) == visible);
 
         private void createPlaylist(bool allowEdit, bool allowSelection)
         {
@@ -278,7 +279,21 @@ namespace osu.Game.Tests.Visual.Multiplayer
                     playlist.Items.Add(new PlaylistItem
                     {
                         ID = i,
-                        Beatmap = { Value = new TestBeatmap(new OsuRuleset().RulesetInfo).BeatmapInfo },
+                        Beatmap =
+                        {
+                            Value = i % 2 == 1
+                                ? new TestBeatmap(new OsuRuleset().RulesetInfo).BeatmapInfo
+                                : new BeatmapInfo
+                                {
+                                    Metadata = new BeatmapMetadata
+                                    {
+                                        Artist = "Artist",
+                                        Author = new User { Username = "Creator name here" },
+                                        Title = "Long title used to check background colour",
+                                    },
+                                    BeatmapSet = new BeatmapSetInfo()
+                                }
+                        },
                         Ruleset = { Value = new OsuRuleset().RulesetInfo },
                         RequiredMods =
                         {

osu.Game.Tests/Visual/Multiplayer/TestSceneFreeModSelectOverlay.cs

@@ -0,0 +1,21 @@
+// Copyright (c) ppy Pty Ltd <contact@ppy.sh>. Licensed under the MIT Licence.
+// See the LICENCE file in the repository root for full licence text.
+
+using NUnit.Framework;
+using osu.Framework.Graphics.Containers;
+using osu.Game.Screens.OnlinePlay;
+
+namespace osu.Game.Tests.Visual.Multiplayer
+{
+    public class TestSceneFreeModSelectOverlay : MultiplayerTestScene
+    {
+        [SetUp]
+        public new void Setup() => Schedule(() =>
+        {
+            Child = new FreeModSelectOverlay
+            {
+                State = { Value = Visibility.Visible }
+            };
+        });
+    }
+}

osu.Game.Tests/Visual/Multiplayer/TestSceneMultiplayerParticipantsList.cs

@@ -8,6 +8,8 @@ using osu.Framework.Graphics.Sprites;
 using osu.Framework.Testing;
 using osu.Framework.Utils;
 using osu.Game.Online.Multiplayer;
+using osu.Game.Rulesets.Mods;
+using osu.Game.Rulesets.Osu.Mods;
 using osu.Game.Screens.OnlinePlay.Multiplayer.Participants;
 using osu.Game.Users;
 using osuTK;
@@ -123,5 +125,32 @@ namespace osu.Game.Tests.Visual.Multiplayer
                 }
             });
         }
+
+        [Test]
+        public void TestUserWithMods()
+        {
+            AddStep("add user", () =>
+            {
+                Client.AddUser(new User
+                {
+                    Id = 0,
+                    Username = "User 0",
+                    CurrentModeRank = RNG.Next(1, 100000),
+                    CoverUrl = @"https://osu.ppy.sh/images/headers/profile-covers/c3.jpg",
+                });
+
+                Client.ChangeUserMods(0, new Mod[]
+                {
+                    new OsuModHardRock(),
+                    new OsuModDifficultyAdjust { ApproachRate = { Value = 1 } }
+                });
+            });
+
+            for (var i = MultiplayerUserState.Idle; i < MultiplayerUserState.Results; i++)
+            {
+                var state = i;
+                AddStep($"set state: {state}", () => Client.ChangeUserState(0, state));
+            }
+        }
     }
 }

osu.Game.Tests/Visual/Multiplayer/TestSceneMultiplayerReadyButton.cs

@@ -6,6 +6,7 @@ using System.Linq;
 using NUnit.Framework;
 using osu.Framework.Allocation;
 using osu.Framework.Audio;
+using osu.Framework.Bindables;
 using osu.Framework.Graphics;
 using osu.Framework.Platform;
 using osu.Framework.Testing;
@@ -26,8 +27,11 @@ namespace osu.Game.Tests.Visual.Multiplayer
     public class TestSceneMultiplayerReadyButton : MultiplayerTestScene
     {
         private MultiplayerReadyButton button;
+        private OnlinePlayBeatmapAvailablilityTracker beatmapTracker;
         private BeatmapSetInfo importedSet;
 
+        private readonly Bindable<PlaylistItem> selectedItem = new Bindable<PlaylistItem>();
+
         private BeatmapManager beatmaps;
         private RulesetStore rulesets;
 
@@ -39,6 +43,13 @@ namespace osu.Game.Tests.Visual.Multiplayer
             Dependencies.Cache(rulesets = new RulesetStore(ContextFactory));
             Dependencies.Cache(beatmaps = new BeatmapManager(LocalStorage, ContextFactory, rulesets, null, audio, host, Beatmap.Default));
             beatmaps.Import(TestResources.GetTestBeatmapForImport(true)).Wait();
+
+            Add(beatmapTracker = new OnlinePlayBeatmapAvailablilityTracker
+            {
+                SelectedItem = { BindTarget = selectedItem }
+            });
+
+            Dependencies.Cache(beatmapTracker);
         }
 
         [SetUp]
@@ -46,20 +57,20 @@ namespace osu.Game.Tests.Visual.Multiplayer
         {
             importedSet = beatmaps.GetAllUsableBeatmapSetsEnumerable(IncludedDetails.All).First();
             Beatmap.Value = beatmaps.GetWorkingBeatmap(importedSet.Beatmaps.First());
+            selectedItem.Value = new PlaylistItem
+            {
+                Beatmap = { Value = Beatmap.Value.BeatmapInfo },
+                Ruleset = { Value = Beatmap.Value.BeatmapInfo.Ruleset },
+            };
 
-            Child = button = new MultiplayerReadyButton
+            if (button != null)
+                Remove(button);
+
+            Add(button = new MultiplayerReadyButton
             {
                 Anchor = Anchor.Centre,
                 Origin = Anchor.Centre,
                 Size = new Vector2(200, 50),
-                SelectedItem =
-                {
-                    Value = new PlaylistItem
-                    {
-                        Beatmap = { Value = Beatmap.Value.BeatmapInfo },
-                        Ruleset = { Value = Beatmap.Value.BeatmapInfo.Ruleset }
-                    }
-                },
                 OnReadyClick = async () =>
                 {
                     readyClickOperation = OngoingOperationTracker.BeginOperation();
@@ -73,7 +84,7 @@ namespace osu.Game.Tests.Visual.Multiplayer
                     await Client.ToggleReady();
                     readyClickOperation.Dispose();
                 }
-            };
+            });
         });
 
         [Test]

osu.Game.Tests/Visual/Multiplayer/TestScenePlaylistsSongSelect.cs

@@ -19,11 +19,11 @@ using osu.Game.Rulesets.Mods;
 using osu.Game.Rulesets.Osu;
 using osu.Game.Rulesets.Osu.Mods;
 using osu.Game.Screens.OnlinePlay.Components;
-using osu.Game.Screens.Select;
+using osu.Game.Screens.OnlinePlay.Playlists;
 
 namespace osu.Game.Tests.Visual.Multiplayer
 {
-    public class TestSceneMatchSongSelect : RoomTestScene
+    public class TestScenePlaylistsSongSelect : RoomTestScene
     {
         [Resolved]
         private BeatmapManager beatmapManager { get; set; }
@@ -32,7 +32,7 @@ namespace osu.Game.Tests.Visual.Multiplayer
 
         private RulesetStore rulesets;
 
-        private TestMatchSongSelect songSelect;
+        private TestPlaylistsSongSelect songSelect;
 
         [BackgroundDependencyLoader]
         private void load(GameHost host, AudioManager audio)
@@ -89,7 +89,7 @@ namespace osu.Game.Tests.Visual.Multiplayer
                 Beatmap.SetDefault();
             });
 
-            AddStep("create song select", () => LoadScreen(songSelect = new TestMatchSongSelect()));
+            AddStep("create song select", () => LoadScreen(songSelect = new TestPlaylistsSongSelect()));
             AddUntilStep("wait for present", () => songSelect.IsCurrentScreen());
         }
 
@@ -176,7 +176,7 @@ namespace osu.Game.Tests.Visual.Multiplayer
             AddAssert("item has rate 1.5", () => Precision.AlmostEquals(1.5, ((OsuModDoubleTime)Room.Playlist.First().RequiredMods[0]).SpeedChange.Value));
         }
 
-        private class TestMatchSongSelect : MatchSongSelect
+        private class TestPlaylistsSongSelect : PlaylistsSongSelect
         {
             public new MatchBeatmapDetailArea BeatmapDetails => (MatchBeatmapDetailArea)base.BeatmapDetails;
         }

osu.Game.Tests/Visual/Online/TestSceneStandAloneChatDisplay.cs

@@ -8,16 +8,16 @@ using osu.Game.Users;
 using osuTK;
 using System;
 using System.Linq;
+using NUnit.Framework;
 using osu.Framework.Graphics.Containers;
 using osu.Game.Graphics.Containers;
 using osu.Game.Overlays.Chat;
+using osuTK.Input;
 
 namespace osu.Game.Tests.Visual.Online
 {
-    public class TestSceneStandAloneChatDisplay : OsuTestScene
+    public class TestSceneStandAloneChatDisplay : OsuManualInputManagerTestScene
     {
-        private readonly Channel testChannel = new Channel();
-
         private readonly User admin = new User
         {
             Username = "HappyStick",
@@ -46,92 +46,97 @@ namespace osu.Game.Tests.Visual.Online
         [Cached]
         private ChannelManager channelManager = new ChannelManager();
 
-        private readonly TestStandAloneChatDisplay chatDisplay;
+        private TestStandAloneChatDisplay chatDisplay;
-        private readonly TestStandAloneChatDisplay chatDisplay2;
+        private int messageIdSequence;
+
+        private Channel testChannel;
 
         public TestSceneStandAloneChatDisplay()
         {
             Add(channelManager);
+        }
 
-            Add(chatDisplay = new TestStandAloneChatDisplay
+        [SetUp]
+        public void SetUp() => Schedule(() =>
+        {
+            messageIdSequence = 0;
+            channelManager.CurrentChannel.Value = testChannel = new Channel();
+
+            Children = new[]
+            {
+                chatDisplay = new TestStandAloneChatDisplay
                 {
                     Anchor = Anchor.CentreLeft,
                     Origin = Anchor.CentreLeft,
                     Margin = new MarginPadding(20),
-                Size = new Vector2(400, 80)
+                    Size = new Vector2(400, 80),
-            });
+                    Channel = { Value = testChannel },
-
+                },
-            Add(chatDisplay2 = new TestStandAloneChatDisplay(true)
+                new TestStandAloneChatDisplay(true)
                 {
                     Anchor = Anchor.CentreRight,
                     Origin = Anchor.CentreRight,
                     Margin = new MarginPadding(20),
-                Size = new Vector2(400, 150)
+                    Size = new Vector2(400, 150),
-            });
+                    Channel = { Value = testChannel },
                 }
+            };
+        });
 
-        protected override void LoadComplete()
+        [Test]
+        public void TestManyMessages()
         {
-            base.LoadComplete();
+            AddStep("message from admin", () => testChannel.AddNewMessages(new Message(messageIdSequence++)
-
-            channelManager.CurrentChannel.Value = testChannel;
-
-            chatDisplay.Channel.Value = testChannel;
-            chatDisplay2.Channel.Value = testChannel;
-
-            int sequence = 0;
-
-            AddStep("message from admin", () => testChannel.AddNewMessages(new Message(sequence++)
             {
                 Sender = admin,
                 Content = "I am a wang!"
             }));
 
-            AddStep("message from team red", () => testChannel.AddNewMessages(new Message(sequence++)
+            AddStep("message from team red", () => testChannel.AddNewMessages(new Message(messageIdSequence++)
             {
                 Sender = redUser,
                 Content = "I am team red."
             }));
 
-            AddStep("message from team red", () => testChannel.AddNewMessages(new Message(sequence++)
+            AddStep("message from team red", () => testChannel.AddNewMessages(new Message(messageIdSequence++)
             {
                 Sender = redUser,
                 Content = "I plan to win!"
             }));
 
-            AddStep("message from team blue", () => testChannel.AddNewMessages(new Message(sequence++)
+            AddStep("message from team blue", () => testChannel.AddNewMessages(new Message(messageIdSequence++)
             {
                 Sender = blueUser,
                 Content = "Not on my watch. Prepare to eat saaaaaaaaaand. Lots and lots of saaaaaaand."
             }));
 
-            AddStep("message from admin", () => testChannel.AddNewMessages(new Message(sequence++)
+            AddStep("message from admin", () => testChannel.AddNewMessages(new Message(messageIdSequence++)
             {
                 Sender = admin,
                 Content = "Okay okay, calm down guys. Let's do this!"
             }));
 
-            AddStep("message from long username", () => testChannel.AddNewMessages(new Message(sequence++)
+            AddStep("message from long username", () => testChannel.AddNewMessages(new Message(messageIdSequence++)
             {
                 Sender = longUsernameUser,
                 Content = "Hi guys, my new username is lit!"
             }));
 
-            AddStep("message with new date", () => testChannel.AddNewMessages(new Message(sequence++)
+            AddStep("message with new date", () => testChannel.AddNewMessages(new Message(messageIdSequence++)
             {
                 Sender = longUsernameUser,
                 Content = "Message from the future!",
                 Timestamp = DateTimeOffset.Now
             }));
 
-            AddUntilStep("ensure still scrolled to bottom", () => chatDisplay.ScrolledToBottom);
+            checkScrolledToBottom();
 
             const int messages_per_call = 10;
             AddRepeatStep("add many messages", () =>
             {
                 for (int i = 0; i < messages_per_call; i++)
                 {
-                    testChannel.AddNewMessages(new Message(sequence++)
+                    testChannel.AddNewMessages(new Message(messageIdSequence++)
                     {
                         Sender = longUsernameUser,
                         Content = "Many messages! " + Guid.NewGuid(),
@@ -153,9 +158,133 @@ namespace osu.Game.Tests.Visual.Online
                 return true;
             });
 
-            AddUntilStep("ensure still scrolled to bottom", () => chatDisplay.ScrolledToBottom);
+            checkScrolledToBottom();
         }
 
+        /// <summary>
+        /// Tests that when a message gets wrapped by the chat display getting contracted while scrolled to bottom, the chat will still keep scrolling down.
+        /// </summary>
+        [Test]
+        public void TestMessageWrappingKeepsAutoScrolling()
+        {
+            fillChat();
+
+            // send message with short words for text wrapping to occur when contracting chat.
+            sendMessage();
+
+            AddStep("contract chat", () => chatDisplay.Width -= 100);
+            checkScrolledToBottom();
+
+            AddStep("send another message", () => testChannel.AddNewMessages(new Message(messageIdSequence++)
+            {
+                Sender = admin,
+                Content = "As we were saying...",
+            }));
+
+            checkScrolledToBottom();
+        }
+
+        [Test]
+        public void TestUserScrollOverride()
+        {
+            fillChat();
+
+            sendMessage();
+            checkScrolledToBottom();
+
+            AddStep("User scroll up", () =>
+            {
+                InputManager.MoveMouseTo(chatDisplay.ScreenSpaceDrawQuad.Centre);
+                InputManager.PressButton(MouseButton.Left);
+                InputManager.MoveMouseTo(chatDisplay.ScreenSpaceDrawQuad.Centre + new Vector2(0, chatDisplay.ScreenSpaceDrawQuad.Height));
+                InputManager.ReleaseButton(MouseButton.Left);
+            });
+
+            checkNotScrolledToBottom();
+            sendMessage();
+            checkNotScrolledToBottom();
+
+            AddRepeatStep("User scroll to bottom", () =>
+            {
+                InputManager.MoveMouseTo(chatDisplay.ScreenSpaceDrawQuad.Centre);
+                InputManager.PressButton(MouseButton.Left);
+                InputManager.MoveMouseTo(chatDisplay.ScreenSpaceDrawQuad.Centre - new Vector2(0, chatDisplay.ScreenSpaceDrawQuad.Height));
+                InputManager.ReleaseButton(MouseButton.Left);
+            }, 5);
+
+            checkScrolledToBottom();
+            sendMessage();
+            checkScrolledToBottom();
+        }
+
+        [Test]
+        public void TestLocalEchoMessageResetsScroll()
+        {
+            fillChat();
+
+            sendMessage();
+            checkScrolledToBottom();
+
+            AddStep("User scroll up", () =>
+            {
+                InputManager.MoveMouseTo(chatDisplay.ScreenSpaceDrawQuad.Centre);
+                InputManager.PressButton(MouseButton.Left);
+                InputManager.MoveMouseTo(chatDisplay.ScreenSpaceDrawQuad.Centre + new Vector2(0, chatDisplay.ScreenSpaceDrawQuad.Height));
+                InputManager.ReleaseButton(MouseButton.Left);
+            });
+
+            checkNotScrolledToBottom();
+            sendMessage();
+            checkNotScrolledToBottom();
+
+            sendLocalMessage();
+            checkScrolledToBottom();
+
+            sendMessage();
+            checkScrolledToBottom();
+        }
+
+        private void fillChat()
+        {
+            AddStep("fill chat", () =>
+            {
+                for (int i = 0; i < 10; i++)
+                {
+                    testChannel.AddNewMessages(new Message(messageIdSequence++)
+                    {
+                        Sender = longUsernameUser,
+                        Content = $"some stuff {Guid.NewGuid()}",
+                    });
+                }
+            });
+
+            checkScrolledToBottom();
+        }
+
+        private void sendMessage()
+        {
+            AddStep("send lorem ipsum", () => testChannel.AddNewMessages(new Message(messageIdSequence++)
+            {
+                Sender = longUsernameUser,
+                Content = "Lorem ipsum dolor sit amet, consectetur adipiscing elit. Fusce et bibendum velit.",
+            }));
+        }
+
+        private void sendLocalMessage()
+        {
+            AddStep("send local echo", () => testChannel.AddLocalEcho(new LocalEchoMessage
+            {
+                Sender = longUsernameUser,
+                Content = "This is a local echo message.",
+            }));
+        }
+
+        private void checkScrolledToBottom() =>
+            AddUntilStep("is scrolled to bottom", () => chatDisplay.ScrolledToBottom);
+
+        private void checkNotScrolledToBottom() =>
+            AddUntilStep("not scrolled to bottom", () => !chatDisplay.ScrolledToBottom);
+
         private class TestStandAloneChatDisplay : StandAloneChatDisplay
         {
             public TestStandAloneChatDisplay(bool textbox = false)
@@ -165,7 +294,7 @@ namespace osu.Game.Tests.Visual.Online
 
             protected DrawableChannel DrawableChannel => InternalChildren.OfType<DrawableChannel>().First();
 
-            protected OsuScrollContainer ScrollContainer => (OsuScrollContainer)((Container)DrawableChannel.Child).Child;
+            protected UserTrackingScrollContainer ScrollContainer => (UserTrackingScrollContainer)((Container)DrawableChannel.Child).Child;
 
             public FillFlowContainer FillFlow => (FillFlowContainer)ScrollContainer.Child;
 

osu.Game.Tests/Visual/Playlists/TestScenePlaylistsLoungeSubScreen.cs

@@ -4,7 +4,6 @@
 using System.Linq;
 using NUnit.Framework;
 using osu.Framework.Allocation;
-using osu.Framework.Graphics;
 using osu.Framework.Screens;
 using osu.Framework.Testing;
 using osu.Game.Graphics.Containers;
@@ -28,12 +27,7 @@ namespace osu.Game.Tests.Visual.Playlists
         {
             base.SetUpSteps();
 
-            AddStep("push screen", () => LoadScreen(loungeScreen = new PlaylistsLoungeSubScreen
+            AddStep("push screen", () => LoadScreen(loungeScreen = new PlaylistsLoungeSubScreen()));
-            {
-                Anchor = Anchor.Centre,
-                Origin = Anchor.Centre,
-                Width = 0.5f,
-            }));
 
             AddUntilStep("wait for present", () => loungeScreen.IsCurrentScreen());
         }

osu.Game.Tests/Visual/UserInterface/TestSceneModIcon.cs

@@ -0,0 +1,21 @@
+// Copyright (c) ppy Pty Ltd <contact@ppy.sh>. Licensed under the MIT Licence.
+// See the LICENCE file in the repository root for full licence text.
+
+using NUnit.Framework;
+using osu.Game.Rulesets.Osu.Mods;
+using osu.Game.Rulesets.UI;
+
+namespace osu.Game.Tests.Visual.UserInterface
+{
+    public class TestSceneModIcon : OsuTestScene
+    {
+        [Test]
+        public void TestChangeModType()
+        {
+            ModIcon icon = null;
+
+            AddStep("create mod icon", () => Child = icon = new ModIcon(new OsuModDoubleTime()));
+            AddStep("change mod", () => icon.Mod = new OsuModEasy());
+        }
+    }
+}

osu.Game.Tests/Visual/UserInterface/TestSceneModSelectOverlay.cs

@@ -8,6 +8,7 @@ using NUnit.Framework;
 using osu.Framework.Allocation;
 using osu.Framework.Bindables;
 using osu.Framework.Graphics;
+using osu.Framework.Graphics.Containers;
 using osu.Framework.Testing;
 using osu.Game.Graphics.Sprites;
 using osu.Game.Graphics.UserInterface;
@@ -38,28 +39,7 @@ namespace osu.Game.Tests.Visual.UserInterface
         }
 
         [SetUp]
-        public void SetUp() => Schedule(() =>
+        public void SetUp() => Schedule(() => createDisplay(() => new TestModSelectOverlay()));
-        {
-            SelectedMods.Value = Array.Empty<Mod>();
-            Children = new Drawable[]
-            {
-                modSelect = new TestModSelectOverlay
-                {
-                    Origin = Anchor.BottomCentre,
-                    Anchor = Anchor.BottomCentre,
-                    SelectedMods = { BindTarget = SelectedMods }
-                },
-
-                modDisplay = new ModDisplay
-                {
-                    Anchor = Anchor.TopRight,
-                    Origin = Anchor.TopRight,
-                    AutoSizeAxes = Axes.Both,
-                    Position = new Vector2(-5, 25),
-                    Current = { BindTarget = modSelect.SelectedMods }
-                }
-            };
-        });
 
         [SetUpSteps]
         public void SetUpSteps()
@@ -67,6 +47,32 @@ namespace osu.Game.Tests.Visual.UserInterface
             AddStep("show", () => modSelect.Show());
         }
 
+        [Test]
+        public void TestAnimationFlushOnClose()
+        {
+            changeRuleset(0);
+
+            AddStep("Select all fun mods", () =>
+            {
+                modSelect.ModSectionsContainer
+                         .Single(c => c.ModType == ModType.DifficultyIncrease)
+                         .SelectAll();
+            });
+
+            AddUntilStep("many mods selected", () => modDisplay.Current.Value.Count >= 5);
+
+            AddStep("trigger deselect and close overlay", () =>
+            {
+                modSelect.ModSectionsContainer
+                         .Single(c => c.ModType == ModType.DifficultyIncrease)
+                         .DeselectAll();
+
+                modSelect.Hide();
+            });
+
+            AddAssert("all mods deselected", () => modDisplay.Current.Value.Count == 0);
+        }
+
         [Test]
         public void TestOsuMods()
         {
@@ -146,6 +152,46 @@ namespace osu.Game.Tests.Visual.UserInterface
             });
         }
 
+        [Test]
+        public void TestNonStacked()
+        {
+            changeRuleset(0);
+
+            AddStep("create overlay", () => createDisplay(() => new TestNonStackedModSelectOverlay()));
+
+            AddStep("show", () => modSelect.Show());
+
+            AddAssert("ensure all buttons are spread out", () => modSelect.ChildrenOfType<ModButton>().All(m => m.Mods.Length <= 1));
+        }
+
+        [Test]
+        public void TestChangeIsValidChangesButtonVisibility()
+        {
+            changeRuleset(0);
+
+            AddAssert("double time visible", () => modSelect.ChildrenOfType<ModButton>().Any(b => b.Mods.Any(m => m is OsuModDoubleTime)));
+
+            AddStep("make double time invalid", () => modSelect.IsValidMod = m => !(m is OsuModDoubleTime));
+            AddUntilStep("double time not visible", () => modSelect.ChildrenOfType<ModButton>().All(b => !b.Mods.Any(m => m is OsuModDoubleTime)));
+            AddAssert("nightcore still visible", () => modSelect.ChildrenOfType<ModButton>().Any(b => b.Mods.Any(m => m is OsuModNightcore)));
+
+            AddStep("make double time valid again", () => modSelect.IsValidMod = m => true);
+            AddUntilStep("double time visible", () => modSelect.ChildrenOfType<ModButton>().Any(b => b.Mods.Any(m => m is OsuModDoubleTime)));
+            AddAssert("nightcore still visible", () => modSelect.ChildrenOfType<ModButton>().Any(b => b.Mods.Any(m => m is OsuModNightcore)));
+        }
+
+        [Test]
+        public void TestChangeIsValidPreservesSelection()
+        {
+            changeRuleset(0);
+
+            AddStep("select DT + HD", () => SelectedMods.Value = new Mod[] { new OsuModDoubleTime(), new OsuModHidden() });
+            AddAssert("DT + HD selected", () => modSelect.ChildrenOfType<ModButton>().Count(b => b.Selected) == 2);
+
+            AddStep("make NF invalid", () => modSelect.IsValidMod = m => !(m is ModNoFail));
+            AddAssert("DT + HD still selected", () => modSelect.ChildrenOfType<ModButton>().Count(b => b.Selected) == 2);
+        }
+
         private void testSingleMod(Mod mod)
         {
             selectNext(mod);
@@ -265,12 +311,37 @@ namespace osu.Game.Tests.Visual.UserInterface
 
         private void checkLabelColor(Func<Color4> getColour) => AddAssert("check label has expected colour", () => modSelect.MultiplierLabel.Colour.AverageColour == getColour());
 
-        private class TestModSelectOverlay : ModSelectOverlay
+        private void createDisplay(Func<TestModSelectOverlay> createOverlayFunc)
+        {
+            SelectedMods.Value = Array.Empty<Mod>();
+            Children = new Drawable[]
+            {
+                modSelect = createOverlayFunc().With(d =>
+                {
+                    d.Origin = Anchor.BottomCentre;
+                    d.Anchor = Anchor.BottomCentre;
+                    d.SelectedMods.BindTarget = SelectedMods;
+                }),
+                modDisplay = new ModDisplay
+                {
+                    Anchor = Anchor.TopRight,
+                    Origin = Anchor.TopRight,
+                    AutoSizeAxes = Axes.Both,
+                    Position = new Vector2(-5, 25),
+                    Current = { BindTarget = modSelect.SelectedMods }
+                }
+            };
+        }
+
+        private class TestModSelectOverlay : SoloModSelectOverlay
         {
             public new Bindable<IReadOnlyList<Mod>> SelectedMods => base.SelectedMods;
 
             public bool AllLoaded => ModSectionsContainer.Children.All(c => c.ModIconsLoaded);
 
+            public new FillFlowContainer<ModSection> ModSectionsContainer =>
+                base.ModSectionsContainer;
+
             public ModButton GetModButton(Mod mod)
             {
                 var section = ModSectionsContainer.Children.Single(s => s.ModType == mod.Type);
@@ -283,5 +354,10 @@ namespace osu.Game.Tests.Visual.UserInterface
             public new Color4 LowMultiplierColour => base.LowMultiplierColour;
             public new Color4 HighMultiplierColour => base.HighMultiplierColour;
         }
+
+        private class TestNonStackedModSelectOverlay : TestModSelectOverlay
+        {
+            protected override bool Stacked => false;
+        }
     }
 }

osu.Game.Tests/Visual/UserInterface/TestSceneModSettings.cs

@@ -151,7 +151,7 @@ namespace osu.Game.Tests.Visual.UserInterface
             AddUntilStep("wait for ready", () => modSelect.State.Value == Visibility.Visible && modSelect.ButtonsLoaded);
         }
 
-        private class TestModSelectOverlay : ModSelectOverlay
+        private class TestModSelectOverlay : SoloModSelectOverlay
         {
             public new VisibilityContainer ModSettingsContainer => base.ModSettingsContainer;
             public new TriangleButton CustomiseButton => base.CustomiseButton;

osu.Game.Tests/osu.Game.Tests.csproj

@@ -7,6 +7,7 @@
     <PackageReference Include="NUnit" Version="3.12.0" />
     <PackageReference Include="NUnit3TestAdapter" Version="3.17.0" />
     <PackageReference Update="Microsoft.EntityFrameworkCore.Sqlite" Version="2.1.4" />
+    <PackageReference Include="Moq" Version="4.16.0" />
   </ItemGroup>
   <PropertyGroup Label="Project">
     <OutputType>WinExe</OutputType>

osu.Game/Database/ArchiveModelManager.cs

@@ -308,7 +308,7 @@ namespace osu.Game.Database
         /// <param name="item">The model to be imported.</param>
         /// <param name="archive">An optional archive to use for model population.</param>
         /// <param name="cancellationToken">An optional cancellation token.</param>
-        public async Task<TModel> Import(TModel item, ArchiveReader archive = null, CancellationToken cancellationToken = default) => await Task.Factory.StartNew(async () =>
+        public virtual async Task<TModel> Import(TModel item, ArchiveReader archive = null, CancellationToken cancellationToken = default) => await Task.Factory.StartNew(async () =>
         {
             cancellationToken.ThrowIfCancellationRequested();
 

osu.Game/Graphics/Containers/UserTrackingScrollContainer.cs

@@ -25,6 +25,8 @@ namespace osu.Game.Graphics.Containers
         /// </summary>
         public bool UserScrolling { get; private set; }
 
+        public void CancelUserScroll() => UserScrolling = false;
+
         public UserTrackingScrollContainer()
         {
         }
@@ -45,5 +47,11 @@ namespace osu.Game.Graphics.Containers
             UserScrolling = false;
             base.ScrollTo(value, animated, distanceDecay);
         }
+
+        public new void ScrollToEnd(bool animated = true, bool allowDuringDrag = false)
+        {
+            UserScrolling = false;
+            base.ScrollToEnd(animated, allowDuringDrag);
+        }
     }
 }

osu.Game/Graphics/UserInterface/DownloadButton.cs

@@ -4,54 +4,38 @@
 using osu.Framework.Allocation;
 using osu.Framework.Bindables;
 using osu.Framework.Graphics;
-using osu.Framework.Graphics.Shapes;
 using osu.Framework.Graphics.Sprites;
 using osu.Game.Online;
 using osuTK;
 
 namespace osu.Game.Graphics.UserInterface
 {
-    public class DownloadButton : OsuAnimatedButton
+    public class DownloadButton : GrayButton
     {
-        public readonly Bindable<DownloadState> State = new Bindable<DownloadState>();
-
-        private readonly SpriteIcon icon;
-        private readonly SpriteIcon checkmark;
-        private readonly Box background;
-
         [Resolved]
         private OsuColour colours { get; set; }
 
+        public readonly Bindable<DownloadState> State = new Bindable<DownloadState>();
+
+        private SpriteIcon checkmark;
+
         public DownloadButton()
+            : base(FontAwesome.Solid.Download)
         {
-            Children = new Drawable[]
+        }
+
+        [BackgroundDependencyLoader]
+        private void load()
         {
-                background = new Box
+            AddInternal(checkmark = new SpriteIcon
-                {
-                    RelativeSizeAxes = Axes.Both,
-                    Depth = float.MaxValue
-                },
-                icon = new SpriteIcon
-                {
-                    Anchor = Anchor.Centre,
-                    Origin = Anchor.Centre,
-                    Size = new Vector2(13),
-                    Icon = FontAwesome.Solid.Download,
-                },
-                checkmark = new SpriteIcon
             {
                 Anchor = Anchor.Centre,
                 Origin = Anchor.Centre,
                 X = 8,
                 Size = Vector2.Zero,
                 Icon = FontAwesome.Solid.Check,
-                }
+            });
-            };
-        }
 
-        [BackgroundDependencyLoader]
-        private void load()
-        {
             State.BindValueChanged(updateState, true);
         }
 
@@ -60,27 +44,27 @@ namespace osu.Game.Graphics.UserInterface
             switch (state.NewValue)
             {
                 case DownloadState.NotDownloaded:
-                    background.FadeColour(colours.Gray4, 500, Easing.InOutExpo);
+                    Background.FadeColour(colours.Gray4, 500, Easing.InOutExpo);
-                    icon.MoveToX(0, 500, Easing.InOutExpo);
+                    Icon.MoveToX(0, 500, Easing.InOutExpo);
                     checkmark.ScaleTo(Vector2.Zero, 500, Easing.InOutExpo);
                     TooltipText = "Download";
                     break;
 
                 case DownloadState.Downloading:
-                    background.FadeColour(colours.Blue, 500, Easing.InOutExpo);
+                    Background.FadeColour(colours.Blue, 500, Easing.InOutExpo);
-                    icon.MoveToX(0, 500, Easing.InOutExpo);
+                    Icon.MoveToX(0, 500, Easing.InOutExpo);
                     checkmark.ScaleTo(Vector2.Zero, 500, Easing.InOutExpo);
                     TooltipText = "Downloading...";
                     break;
 
                 case DownloadState.Importing:
-                    background.FadeColour(colours.Yellow, 500, Easing.InOutExpo);
+                    Background.FadeColour(colours.Yellow, 500, Easing.InOutExpo);
                     TooltipText = "Importing";
                     break;
 
                 case DownloadState.LocallyAvailable:
-                    background.FadeColour(colours.Green, 500, Easing.InOutExpo);
+                    Background.FadeColour(colours.Green, 500, Easing.InOutExpo);
-                    icon.MoveToX(-8, 500, Easing.InOutExpo);
+                    Icon.MoveToX(-8, 500, Easing.InOutExpo);
                     checkmark.ScaleTo(new Vector2(13), 500, Easing.InOutExpo);
                     break;
             }

osu.Game/Graphics/UserInterface/GrayButton.cs

@@ -0,0 +1,48 @@
+// Copyright (c) ppy Pty Ltd <contact@ppy.sh>. Licensed under the MIT Licence.
+// See the LICENCE file in the repository root for full licence text.
+
+using osu.Framework.Allocation;
+using osu.Framework.Graphics;
+using osu.Framework.Graphics.Shapes;
+using osu.Framework.Graphics.Sprites;
+using osuTK;
+
+namespace osu.Game.Graphics.UserInterface
+{
+    public class GrayButton : OsuAnimatedButton
+    {
+        protected SpriteIcon Icon { get; private set; }
+        protected Box Background { get; private set; }
+
+        private readonly IconUsage icon;
+
+        [Resolved]
+        private OsuColour colours { get; set; }
+
+        public GrayButton(IconUsage icon)
+        {
+            this.icon = icon;
+        }
+
+        [BackgroundDependencyLoader]
+        private void load()
+        {
+            Children = new Drawable[]
+            {
+                Background = new Box
+                {
+                    Colour = colours.Gray4,
+                    RelativeSizeAxes = Axes.Both,
+                    Depth = float.MaxValue
+                },
+                Icon = new SpriteIcon
+                {
+                    Anchor = Anchor.Centre,
+                    Origin = Anchor.Centre,
+                    Size = new Vector2(13),
+                    Icon = icon,
+                },
+            };
+        }
+    }
+}

osu.Game/Graphics/UserInterface/Nub.cs

@@ -42,13 +42,7 @@ namespace osu.Game.Graphics.UserInterface
                 },
             };
 
-            Current.ValueChanged += filled =>
+            Current.ValueChanged += filled => fill.FadeTo(filled.NewValue ? 1 : 0, 200, Easing.OutQuint);
-            {
-                if (filled.NewValue)
-                    fill.FadeIn(200, Easing.OutQuint);
-                else
-                    fill.FadeTo(0.01f, 200, Easing.OutQuint); //todo: remove once we figure why containers aren't drawing at all times
-            };
         }
 
         [BackgroundDependencyLoader]

osu.Game/Graphics/UserInterface/OsuCheckbox.cs

@@ -5,6 +5,7 @@ using osu.Framework.Allocation;
 using osu.Framework.Audio;
 using osu.Framework.Audio.Sample;
 using osu.Framework.Graphics;
+using osu.Framework.Graphics.Sprites;
 using osu.Framework.Graphics.UserInterface;
 using osu.Framework.Input.Events;
 using osu.Game.Graphics.Containers;
@@ -18,6 +19,11 @@ namespace osu.Game.Graphics.UserInterface
         public Color4 UncheckedColor { get; set; } = Color4.White;
         public int FadeDuration { get; set; }
 
+        /// <summary>
+        /// Whether to play sounds when the state changes as a result of user interaction.
+        /// </summary>
+        protected virtual bool PlaySoundsOnUserChange => true;
+
         public string LabelText
         {
             set
@@ -43,7 +49,7 @@ namespace osu.Game.Graphics.UserInterface
         private SampleChannel sampleChecked;
         private SampleChannel sampleUnchecked;
 
-        public OsuCheckbox()
+        public OsuCheckbox(bool nubOnRight = true)
         {
             AutoSizeAxes = Axes.Y;
             RelativeSizeAxes = Axes.X;
@@ -52,26 +58,42 @@ namespace osu.Game.Graphics.UserInterface
 
             Children = new Drawable[]
             {
-                labelText = new OsuTextFlowContainer
+                labelText = new OsuTextFlowContainer(ApplyLabelParameters)
                 {
                     AutoSizeAxes = Axes.Y,
                     RelativeSizeAxes = Axes.X,
-                    Padding = new MarginPadding { Right = Nub.EXPANDED_SIZE + nub_padding }
-                },
-                Nub = new Nub
-                {
-                    Anchor = Anchor.CentreRight,
-                    Origin = Anchor.CentreRight,
-                    Margin = new MarginPadding { Right = nub_padding },
                 },
+                Nub = new Nub(),
                 new HoverClickSounds()
             };
 
+            if (nubOnRight)
+            {
+                Nub.Anchor = Anchor.CentreRight;
+                Nub.Origin = Anchor.CentreRight;
+                Nub.Margin = new MarginPadding { Right = nub_padding };
+                labelText.Padding = new MarginPadding { Right = Nub.EXPANDED_SIZE + nub_padding * 2 };
+            }
+            else
+            {
+                Nub.Anchor = Anchor.CentreLeft;
+                Nub.Origin = Anchor.CentreLeft;
+                Nub.Margin = new MarginPadding { Left = nub_padding };
+                labelText.Padding = new MarginPadding { Left = Nub.EXPANDED_SIZE + nub_padding * 2 };
+            }
+
             Nub.Current.BindTo(Current);
 
             Current.DisabledChanged += disabled => labelText.Alpha = Nub.Alpha = disabled ? 0.3f : 1;
         }
 
+        /// <summary>
+        /// A function which can be overridden to change the parameters of the label's text.
+        /// </summary>
+        protected virtual void ApplyLabelParameters(SpriteText text)
+        {
+        }
+
         [BackgroundDependencyLoader]
         private void load(AudioManager audio)
         {
@@ -96,10 +118,14 @@ namespace osu.Game.Graphics.UserInterface
         protected override void OnUserChange(bool value)
         {
             base.OnUserChange(value);
+
+            if (PlaySoundsOnUserChange)
+            {
                 if (value)
                     sampleChecked?.Play();
                 else
                     sampleUnchecked?.Play();
             }
         }
+    }
 }

osu.Game/Online/API/APIDownloadRequest.cs

@@ -1,6 +1,7 @@
 // Copyright (c) ppy Pty Ltd <contact@ppy.sh>. Licensed under the MIT Licence.
 // See the LICENCE file in the repository root for full licence text.
 
+using System;
 using System.IO;
 using osu.Framework.IO.Network;
 
@@ -28,13 +29,19 @@ namespace osu.Game.Online.API
 
         private void request_Progress(long current, long total) => API.Schedule(() => Progressed?.Invoke(current, total));
 
-        protected APIDownloadRequest()
+        protected void TriggerSuccess(string filename)
         {
-            base.Success += onSuccess;
+            if (this.filename != null)
+                throw new InvalidOperationException("Attempted to trigger success more than once");
+
+            this.filename = filename;
+
+            TriggerSuccess();
         }
 
-        private void onSuccess()
+        internal override void TriggerSuccess()
         {
+            base.TriggerSuccess();
             Success?.Invoke(filename);
         }
 

osu.Game/Online/API/APIMod.cs

@@ -23,6 +23,7 @@ namespace osu.Game.Online.API
 
         [JsonProperty("settings")]
         [Key(1)]
+        [MessagePackFormatter(typeof(ModSettingsDictionaryFormatter))]
         public Dictionary<string, object> Settings { get; set; } = new Dictionary<string, object>();
 
         [JsonConstructor]

osu.Game/Online/API/ArchiveDownloadRequest.cs

@@ -10,7 +10,7 @@ namespace osu.Game.Online.API
     {
         public readonly TModel Model;
 
-        public float Progress;
+        public float Progress { get; private set; }
 
         public event Action<float> DownloadProgressed;
 
@@ -18,7 +18,13 @@ namespace osu.Game.Online.API
         {
             Model = model;
 
-            Progressed += (current, total) => DownloadProgressed?.Invoke(Progress = (float)current / total);
+            Progressed += (current, total) => SetProgress((float)current / total);
+        }
+
+        protected void SetProgress(float progress)
+        {
+            Progress = progress;
+            DownloadProgressed?.Invoke(progress);
         }
     }
 }

osu.Game/Online/API/ModSettingsDictionaryFormatter.cs

@@ -0,0 +1,67 @@
+// Copyright (c) ppy Pty Ltd <contact@ppy.sh>. Licensed under the MIT Licence.
+// See the LICENCE file in the repository root for full licence text.
+
+using System.Buffers;
+using System.Collections.Generic;
+using System.Text;
+using MessagePack;
+using MessagePack.Formatters;
+using osu.Framework.Bindables;
+
+namespace osu.Game.Online.API
+{
+    public class ModSettingsDictionaryFormatter : IMessagePackFormatter<Dictionary<string, object>>
+    {
+        public void Serialize(ref MessagePackWriter writer, Dictionary<string, object> value, MessagePackSerializerOptions options)
+        {
+            var primitiveFormatter = PrimitiveObjectFormatter.Instance;
+
+            writer.WriteArrayHeader(value.Count);
+
+            foreach (var kvp in value)
+            {
+                var stringBytes = new ReadOnlySequence<byte>(Encoding.UTF8.GetBytes(kvp.Key));
+                writer.WriteString(in stringBytes);
+
+                switch (kvp.Value)
+                {
+                    case Bindable<double> d:
+                        primitiveFormatter.Serialize(ref writer, d.Value, options);
+                        break;
+
+                    case Bindable<int> i:
+                        primitiveFormatter.Serialize(ref writer, i.Value, options);
+                        break;
+
+                    case Bindable<float> f:
+                        primitiveFormatter.Serialize(ref writer, f.Value, options);
+                        break;
+
+                    case Bindable<bool> b:
+                        primitiveFormatter.Serialize(ref writer, b.Value, options);
+                        break;
+
+                    default:
+                        // fall back for non-bindable cases.
+                        primitiveFormatter.Serialize(ref writer, kvp.Value, options);
+                        break;
+                }
+            }
+        }
+
+        public Dictionary<string, object> Deserialize(ref MessagePackReader reader, MessagePackSerializerOptions options)
+        {
+            var output = new Dictionary<string, object>();
+
+            int itemCount = reader.ReadArrayHeader();
+
+            for (int i = 0; i < itemCount; i++)
+            {
+                output[reader.ReadString()] =
+                    PrimitiveObjectFormatter.Instance.Deserialize(ref reader, options);
+            }
+
+            return output;
+        }
+    }
+}

osu.Game/Online/DownloadTrackingComposite.cs

@@ -2,6 +2,7 @@
 // See the LICENCE file in the repository root for full licence text.
 
 using System;
+using JetBrains.Annotations;
 using osu.Framework.Allocation;
 using osu.Framework.Bindables;
 using osu.Framework.Graphics.Containers;
@@ -20,7 +21,7 @@ namespace osu.Game.Online
         protected readonly Bindable<TModel> Model = new Bindable<TModel>();
 
         [Resolved(CanBeNull = true)]
-        private TModelManager manager { get; set; }
+        protected TModelManager Manager { get; private set; }
 
         /// <summary>
         /// Holds the current download state of the <typeparamref name="TModel"/>, whether is has already been downloaded, is in progress, or is not downloaded.
@@ -46,25 +47,41 @@ namespace osu.Game.Online
             {
                 if (modelInfo.NewValue == null)
                     attachDownload(null);
-                else if (manager?.IsAvailableLocally(modelInfo.NewValue) == true)
+                else if (IsModelAvailableLocally())
                     State.Value = DownloadState.LocallyAvailable;
                 else
-                    attachDownload(manager?.GetExistingDownload(modelInfo.NewValue));
+                    attachDownload(Manager?.GetExistingDownload(modelInfo.NewValue));
             }, true);
 
-            if (manager == null)
+            if (Manager == null)
                 return;
 
-            managerDownloadBegan = manager.DownloadBegan.GetBoundCopy();
+            managerDownloadBegan = Manager.DownloadBegan.GetBoundCopy();
             managerDownloadBegan.BindValueChanged(downloadBegan);
-            managerDownloadFailed = manager.DownloadFailed.GetBoundCopy();
+            managerDownloadFailed = Manager.DownloadFailed.GetBoundCopy();
             managerDownloadFailed.BindValueChanged(downloadFailed);
-            managedUpdated = manager.ItemUpdated.GetBoundCopy();
+            managedUpdated = Manager.ItemUpdated.GetBoundCopy();
             managedUpdated.BindValueChanged(itemUpdated);
-            managerRemoved = manager.ItemRemoved.GetBoundCopy();
+            managerRemoved = Manager.ItemRemoved.GetBoundCopy();
             managerRemoved.BindValueChanged(itemRemoved);
         }
 
+        /// <summary>
+        /// Checks that a database model matches the one expected to be downloaded.
+        /// </summary>
+        /// <example>
+        /// For online play, this could be used to check that the databased model matches the online beatmap.
+        /// </example>
+        /// <param name="databasedModel">The model in database.</param>
+        protected virtual bool VerifyDatabasedModel([NotNull] TModel databasedModel) => true;
+
+        /// <summary>
+        /// Whether the given model is available in the database.
+        /// By default, this calls <see cref="IModelDownloader{TModel}.IsAvailableLocally"/>,
+        /// but can be overriden to add additional checks for verifying the model in database.
+        /// </summary>
+        protected virtual bool IsModelAvailableLocally() => Manager?.IsAvailableLocally(Model.Value) == true;
+
         private void downloadBegan(ValueChangedEvent<WeakReference<ArchiveDownloadRequest<TModel>>> weakRequest)
         {
             if (weakRequest.NewValue.TryGetTarget(out var request))
@@ -134,22 +151,34 @@ namespace osu.Game.Online
         private void itemUpdated(ValueChangedEvent<WeakReference<TModel>> weakItem)
         {
             if (weakItem.NewValue.TryGetTarget(out var item))
-                setDownloadStateFromManager(item, DownloadState.LocallyAvailable);
+            {
+                Schedule(() =>
+                {
+                    if (!item.Equals(Model.Value))
+                        return;
+
+                    if (!VerifyDatabasedModel(item))
+                    {
+                        State.Value = DownloadState.NotDownloaded;
+                        return;
+                    }
+
+                    State.Value = DownloadState.LocallyAvailable;
+                });
+            }
         }
 
         private void itemRemoved(ValueChangedEvent<WeakReference<TModel>> weakItem)
         {
             if (weakItem.NewValue.TryGetTarget(out var item))
-                setDownloadStateFromManager(item, DownloadState.NotDownloaded);
-        }
-
-        private void setDownloadStateFromManager(TModel s, DownloadState state) => Schedule(() =>
             {
-            if (!s.Equals(Model.Value))
+                Schedule(() =>
-                return;
+                {
-
+                    if (item.Equals(Model.Value))
-            State.Value = state;
+                        State.Value = DownloadState.NotDownloaded;
                 });
+            }
+        }
 
         #region Disposal
 

osu.Game/Online/Multiplayer/IMultiplayerClient.cs

@@ -1,7 +1,9 @@
 // Copyright (c) ppy Pty Ltd <contact@ppy.sh>. Licensed under the MIT Licence.
 // See the LICENCE file in the repository root for full licence text.
 
+using System.Collections.Generic;
 using System.Threading.Tasks;
+using osu.Game.Online.API;
 using osu.Game.Online.Rooms;
 
 namespace osu.Game.Online.Multiplayer
@@ -55,6 +57,13 @@ namespace osu.Game.Online.Multiplayer
         /// <param name="beatmapAvailability">The new beatmap availability state of the user.</param>
         Task UserBeatmapAvailabilityChanged(int userId, BeatmapAvailability beatmapAvailability);
 
+        /// <summary>
+        /// Signals that a user in this room changed their local mods.
+        /// </summary>
+        /// <param name="userId">The ID of the user whose mods have changed.</param>
+        /// <param name="mods">The user's new local mods.</param>
+        Task UserModsChanged(int userId, IEnumerable<APIMod> mods);
+
         /// <summary>
         /// Signals that a match is to be started. This will *only* be sent to clients which are to begin loading at this point.
         /// </summary>

osu.Game/Online/Multiplayer/IMultiplayerRoomServer.cs

@@ -1,7 +1,9 @@
 // Copyright (c) ppy Pty Ltd <contact@ppy.sh>. Licensed under the MIT Licence.
 // See the LICENCE file in the repository root for full licence text.
 
+using System.Collections.Generic;
 using System.Threading.Tasks;
+using osu.Game.Online.API;
 using osu.Game.Online.Rooms;
 
 namespace osu.Game.Online.Multiplayer
@@ -47,6 +49,12 @@ namespace osu.Game.Online.Multiplayer
         /// <param name="newBeatmapAvailability">The proposed new beatmap availability state.</param>
         Task ChangeBeatmapAvailability(BeatmapAvailability newBeatmapAvailability);
 
+        /// <summary>
+        /// Change the local user's mods in the currently joined room.
+        /// </summary>
+        /// <param name="newMods">The proposed new mods, excluding any required by the room itself.</param>
+        Task ChangeUserMods(IEnumerable<APIMod> newMods);
+
         /// <summary>
         /// As the host of a room, start the match.
         /// </summary>

osu.Game/Online/Multiplayer/MultiplayerClient.cs

@@ -4,6 +4,7 @@
 #nullable enable
 
 using System;
+using System.Collections.Generic;
 using System.Diagnostics;
 using System.Threading;
 using System.Threading.Tasks;
@@ -91,6 +92,7 @@ namespace osu.Game.Online.Multiplayer
             connection.On(nameof(IMultiplayerClient.LoadRequested), ((IMultiplayerClient)this).LoadRequested);
             connection.On(nameof(IMultiplayerClient.MatchStarted), ((IMultiplayerClient)this).MatchStarted);
             connection.On(nameof(IMultiplayerClient.ResultsReady), ((IMultiplayerClient)this).ResultsReady);
+            connection.On<int, IEnumerable<APIMod>>(nameof(IMultiplayerClient.UserModsChanged), ((IMultiplayerClient)this).UserModsChanged);
 
             connection.Closed += async ex =>
             {
@@ -189,6 +191,14 @@ namespace osu.Game.Online.Multiplayer
             return connection.InvokeAsync(nameof(IMultiplayerServer.ChangeBeatmapAvailability), newBeatmapAvailability);
         }
 
+        public override Task ChangeUserMods(IEnumerable<APIMod> newMods)
+        {
+            if (!isConnected.Value)
+                return Task.CompletedTask;
+
+            return connection.InvokeAsync(nameof(IMultiplayerServer.ChangeUserMods), newMods);
+        }
+
         public override Task StartMatch()
         {
             if (!isConnected.Value)

osu.Game/Online/Multiplayer/MultiplayerRoomSettings.cs

@@ -30,15 +30,24 @@ namespace osu.Game.Online.Multiplayer
 
         [NotNull]
         [Key(4)]
-        public IEnumerable<APIMod> Mods { get; set; } = Enumerable.Empty<APIMod>();
+        public IEnumerable<APIMod> RequiredMods { get; set; } = Enumerable.Empty<APIMod>();
+
+        [NotNull]
+        [Key(5)]
+        public IEnumerable<APIMod> AllowedMods { get; set; } = Enumerable.Empty<APIMod>();
 
         public bool Equals(MultiplayerRoomSettings other)
             => BeatmapID == other.BeatmapID
                && BeatmapChecksum == other.BeatmapChecksum
-               && Mods.SequenceEqual(other.Mods)
+               && RequiredMods.SequenceEqual(other.RequiredMods)
+               && AllowedMods.SequenceEqual(other.AllowedMods)
                && RulesetID == other.RulesetID
                && Name.Equals(other.Name, StringComparison.Ordinal);
 
-        public override string ToString() => $"Name:{Name} Beatmap:{BeatmapID} ({BeatmapChecksum}) Mods:{string.Join(',', Mods)} Ruleset:{RulesetID}";
+        public override string ToString() => $"Name:{Name}"
+                                             + $" Beatmap:{BeatmapID} ({BeatmapChecksum})"
+                                             + $" RequiredMods:{string.Join(',', RequiredMods)}"
+                                             + $" AllowedMods:{string.Join(',', AllowedMods)}"
+                                             + $" Ruleset:{RulesetID}";
     }
 }

osu.Game/Online/Multiplayer/MultiplayerRoomUser.cs

@@ -4,8 +4,12 @@
 #nullable enable
 
 using System;
+using System.Collections.Generic;
+using System.Linq;
+using JetBrains.Annotations;
 using MessagePack;
 using Newtonsoft.Json;
+using osu.Game.Online.API;
 using osu.Game.Online.Rooms;
 using osu.Game.Users;
 
@@ -27,6 +31,13 @@ namespace osu.Game.Online.Multiplayer
         [Key(2)]
         public BeatmapAvailability BeatmapAvailability { get; set; } = BeatmapAvailability.LocallyAvailable();
 
+        /// <summary>
+        /// Any mods applicable only to the local user.
+        /// </summary>
+        [Key(3)]
+        [NotNull]
+        public IEnumerable<APIMod> Mods { get; set; } = Enumerable.Empty<APIMod>();
+
         [IgnoreMember]
         public User? User { get; set; }
 

osu.Game/Online/Multiplayer/StatefulMultiplayerClient.cs

@@ -21,6 +21,7 @@ using osu.Game.Online.API.Requests.Responses;
 using osu.Game.Online.Rooms;
 using osu.Game.Online.Rooms.RoomStatuses;
 using osu.Game.Rulesets;
+using osu.Game.Rulesets.Mods;
 using osu.Game.Users;
 using osu.Game.Utils;
 
@@ -191,7 +192,8 @@ namespace osu.Game.Online.Multiplayer
                 BeatmapID = item.GetOr(existingPlaylistItem).BeatmapID,
                 BeatmapChecksum = item.GetOr(existingPlaylistItem).Beatmap.Value.MD5Hash,
                 RulesetID = item.GetOr(existingPlaylistItem).RulesetID,
-                Mods = item.HasValue ? item.Value.AsNonNull().RequiredMods.Select(m => new APIMod(m)).ToList() : Room.Settings.Mods
+                RequiredMods = item.HasValue ? item.Value.AsNonNull().RequiredMods.Select(m => new APIMod(m)).ToList() : Room.Settings.RequiredMods,
+                AllowedMods = item.HasValue ? item.Value.AsNonNull().AllowedMods.Select(m => new APIMod(m)).ToList() : Room.Settings.AllowedMods
             });
         }
 
@@ -229,6 +231,14 @@ namespace osu.Game.Online.Multiplayer
 
         public abstract Task ChangeBeatmapAvailability(BeatmapAvailability newBeatmapAvailability);
 
+        /// <summary>
+        /// Change the local user's mods in the currently joined room.
+        /// </summary>
+        /// <param name="newMods">The proposed new mods, excluding any required by the room itself.</param>
+        public Task ChangeUserMods(IEnumerable<Mod> newMods) => ChangeUserMods(newMods.Select(m => new APIMod(m)).ToList());
+
+        public abstract Task ChangeUserMods(IEnumerable<APIMod> newMods);
+
         public abstract Task StartMatch();
 
         Task IMultiplayerClient.RoomStateChanged(MultiplayerRoomState state)
@@ -377,6 +387,27 @@ namespace osu.Game.Online.Multiplayer
             return Task.CompletedTask;
         }
 
+        public Task UserModsChanged(int userId, IEnumerable<APIMod> mods)
+        {
+            if (Room == null)
+                return Task.CompletedTask;
+
+            Scheduler.Add(() =>
+            {
+                var user = Room?.Users.SingleOrDefault(u => u.UserID == userId);
+
+                // errors here are not critical - user mods are mostly for display.
+                if (user == null)
+                    return;
+
+                user.Mods = mods;
+
+                RoomUpdated?.Invoke();
+            }, false);
+
+            return Task.CompletedTask;
+        }
+
         Task IMultiplayerClient.LoadRequested()
         {
             if (Room == null)
@@ -500,7 +531,8 @@ namespace osu.Game.Online.Multiplayer
             beatmap.MD5Hash = settings.BeatmapChecksum;
 
             var ruleset = rulesets.GetRuleset(settings.RulesetID).CreateInstance();
-            var mods = settings.Mods.Select(m => m.ToMod(ruleset));
+            var mods = settings.RequiredMods.Select(m => m.ToMod(ruleset));
+            var allowedMods = settings.AllowedMods.Select(m => m.ToMod(ruleset));
 
             PlaylistItem playlistItem = new PlaylistItem
             {
@@ -510,6 +542,7 @@ namespace osu.Game.Online.Multiplayer
             };
 
             playlistItem.RequiredMods.AddRange(mods);
+            playlistItem.AllowedMods.AddRange(allowedMods);
 
             apiRoom.Playlist.Clear(); // Clearing should be unnecessary, but here for sanity.
             apiRoom.Playlist.Add(playlistItem);

osu.Game/Online/Rooms/BeatmapAvailability.cs

@@ -23,17 +23,17 @@ namespace osu.Game.Online.Rooms
         /// The beatmap's downloading progress, null when not in <see cref="DownloadState.Downloading"/> state.
         /// </summary>
         [Key(1)]
-        public readonly double? DownloadProgress;
+        public readonly float? DownloadProgress;
 
         [JsonConstructor]
-        public BeatmapAvailability(DownloadState state, double? downloadProgress = null)
+        public BeatmapAvailability(DownloadState state, float? downloadProgress = null)
         {
             State = state;
             DownloadProgress = downloadProgress;
         }
 
         public static BeatmapAvailability NotDownloaded() => new BeatmapAvailability(DownloadState.NotDownloaded);
-        public static BeatmapAvailability Downloading(double progress) => new BeatmapAvailability(DownloadState.Downloading, progress);
+        public static BeatmapAvailability Downloading(float progress) => new BeatmapAvailability(DownloadState.Downloading, progress);
         public static BeatmapAvailability Importing() => new BeatmapAvailability(DownloadState.Importing);
         public static BeatmapAvailability LocallyAvailable() => new BeatmapAvailability(DownloadState.LocallyAvailable);
 

osu.Game/Online/Rooms/OnlinePlayBeatmapAvailablilityTracker.cs

@@ -0,0 +1,92 @@
+// Copyright (c) ppy Pty Ltd <contact@ppy.sh>. Licensed under the MIT Licence.
+// See the LICENCE file in the repository root for full licence text.
+
+using System;
+using System.Linq;
+using osu.Framework.Bindables;
+using osu.Framework.Logging;
+using osu.Game.Beatmaps;
+
+namespace osu.Game.Online.Rooms
+{
+    /// <summary>
+    /// Represent a checksum-verifying beatmap availability tracker usable for online play screens.
+    ///
+    /// This differs from a regular download tracking composite as this accounts for the
+    /// databased beatmap set's checksum, to disallow from playing with an altered version of the beatmap.
+    /// </summary>
+    public class OnlinePlayBeatmapAvailablilityTracker : DownloadTrackingComposite<BeatmapSetInfo, BeatmapManager>
+    {
+        public readonly IBindable<PlaylistItem> SelectedItem = new Bindable<PlaylistItem>();
+
+        /// <summary>
+        /// The availability state of the currently selected playlist item.
+        /// </summary>
+        public IBindable<BeatmapAvailability> Availability => availability;
+
+        private readonly Bindable<BeatmapAvailability> availability = new Bindable<BeatmapAvailability>();
+
+        public OnlinePlayBeatmapAvailablilityTracker()
+        {
+            State.BindValueChanged(_ => updateAvailability());
+            Progress.BindValueChanged(_ => updateAvailability(), true);
+        }
+
+        protected override void LoadComplete()
+        {
+            base.LoadComplete();
+
+            SelectedItem.BindValueChanged(item => Model.Value = item.NewValue?.Beatmap.Value.BeatmapSet, true);
+        }
+
+        protected override bool VerifyDatabasedModel(BeatmapSetInfo databasedSet)
+        {
+            int? beatmapId = SelectedItem.Value.Beatmap.Value.OnlineBeatmapID;
+            string checksum = SelectedItem.Value.Beatmap.Value.MD5Hash;
+
+            var matchingBeatmap = databasedSet.Beatmaps.FirstOrDefault(b => b.OnlineBeatmapID == beatmapId && b.MD5Hash == checksum);
+
+            if (matchingBeatmap == null)
+            {
+                Logger.Log("The imported beatmap set does not match the online version.", LoggingTarget.Runtime, LogLevel.Important);
+                return false;
+            }
+
+            return true;
+        }
+
+        protected override bool IsModelAvailableLocally()
+        {
+            int? beatmapId = SelectedItem.Value.Beatmap.Value.OnlineBeatmapID;
+            string checksum = SelectedItem.Value.Beatmap.Value.MD5Hash;
+
+            var beatmap = Manager.QueryBeatmap(b => b.OnlineBeatmapID == beatmapId && b.MD5Hash == checksum);
+            return beatmap?.BeatmapSet.DeletePending == false;
+        }
+
+        private void updateAvailability()
+        {
+            switch (State.Value)
+            {
+                case DownloadState.NotDownloaded:
+                    availability.Value = BeatmapAvailability.NotDownloaded();
+                    break;
+
+                case DownloadState.Downloading:
+                    availability.Value = BeatmapAvailability.Downloading((float)Progress.Value);
+                    break;
+
+                case DownloadState.Importing:
+                    availability.Value = BeatmapAvailability.Importing();
+                    break;
+
+                case DownloadState.LocallyAvailable:
+                    availability.Value = BeatmapAvailability.LocallyAvailable();
+                    break;
+
+                default:
+                    throw new ArgumentOutOfRangeException(nameof(State));
+            }
+        }
+    }
+}

osu.Game/OsuGame.cs

@@ -468,6 +468,12 @@ namespace osu.Game
         private void modsChanged(ValueChangedEvent<IReadOnlyList<Mod>> mods)
         {
             updateModDefaults();
+
+            if (!ModUtils.CheckValidForGameplay(mods.NewValue, out var invalid))
+            {
+                // ensure we always have a valid set of mods.
+                SelectedMods.Value = mods.NewValue.Except(invalid).ToArray();
+            }
         }
 
         private void updateModDefaults()

osu.Game/Overlays/Chat/DrawableChannel.cs

@@ -16,6 +16,7 @@ using osu.Framework.Graphics.Shapes;
 using osu.Game.Graphics;
 using osu.Framework.Extensions.Color4Extensions;
 using osu.Framework.Graphics.Sprites;
+using osu.Framework.Utils;
 using osu.Game.Graphics.Sprites;
 
 namespace osu.Game.Overlays.Chat
@@ -24,7 +25,7 @@ namespace osu.Game.Overlays.Chat
     {
         public readonly Channel Channel;
         protected FillFlowContainer ChatLineFlow;
-        private OsuScrollContainer scroll;
+        private ChannelScrollContainer scroll;
 
         private bool scrollbarVisible = true;
 
@@ -56,7 +57,7 @@ namespace osu.Game.Overlays.Chat
             {
                 RelativeSizeAxes = Axes.Both,
                 Masking = true,
-                Child = scroll = new OsuScrollContainer
+                Child = scroll = new ChannelScrollContainer
                 {
                     ScrollbarVisible = scrollbarVisible,
                     RelativeSizeAxes = Axes.Both,
@@ -80,12 +81,6 @@ namespace osu.Game.Overlays.Chat
             Channel.PendingMessageResolved += pendingMessageResolved;
         }
 
-        protected override void LoadComplete()
-        {
-            base.LoadComplete();
-            scrollToEnd();
-        }
-
         protected override void Dispose(bool isDisposing)
         {
             base.Dispose(isDisposing);
@@ -113,8 +108,6 @@ namespace osu.Game.Overlays.Chat
                 ChatLineFlow.Clear();
             }
 
-            bool shouldScrollToEnd = scroll.IsScrolledToEnd(10) || !chatLines.Any() || newMessages.Any(m => m is LocalMessage);
-
             // Add up to last Channel.MAX_HISTORY messages
             var displayMessages = newMessages.Skip(Math.Max(0, newMessages.Count() - Channel.MAX_HISTORY));
 
@@ -153,8 +146,10 @@ namespace osu.Game.Overlays.Chat
                 }
             }
 
-            if (shouldScrollToEnd)
+            // due to the scroll adjusts from old messages removal above, a scroll-to-end must be enforced,
-                scrollToEnd();
+            // to avoid making the container think the user has scrolled back up and unwantedly disable auto-scrolling.
+            if (newMessages.Any(m => m is LocalMessage))
+                scroll.ScrollToEnd();
         });
 
         private void pendingMessageResolved(Message existing, Message updated) => Schedule(() =>
@@ -178,8 +173,6 @@ namespace osu.Game.Overlays.Chat
 
         private IEnumerable<ChatLine> chatLines => ChatLineFlow.Children.OfType<ChatLine>();
 
-        private void scrollToEnd() => ScheduleAfterChildren(() => scroll.ScrollToEnd());
-
         public class DaySeparator : Container
         {
             public float TextSize
@@ -243,5 +236,51 @@ namespace osu.Game.Overlays.Chat
                 };
             }
         }
+
+        /// <summary>
+        /// An <see cref="OsuScrollContainer"/> with functionality to automatically scroll whenever the maximum scrollable distance increases.
+        /// </summary>
+        private class ChannelScrollContainer : UserTrackingScrollContainer
+        {
+            /// <summary>
+            /// The chat will be automatically scrolled to end if and only if
+            /// the distance between the current scroll position and the end of the scroll
+            /// is less than this value.
+            /// </summary>
+            private const float auto_scroll_leniency = 10f;
+
+            private float? lastExtent;
+
+            protected override void OnUserScroll(float value, bool animated = true, double? distanceDecay = default)
+            {
+                base.OnUserScroll(value, animated, distanceDecay);
+                lastExtent = null;
+            }
+
+            protected override void Update()
+            {
+                base.Update();
+
+                // If the user has scrolled to the bottom of the container, we should resume tracking new content.
+                if (UserScrolling && IsScrolledToEnd(auto_scroll_leniency))
+                    CancelUserScroll();
+
+                // If the user hasn't overridden our behaviour and there has been new content added to the container, we should update our scroll position to track it.
+                bool requiresScrollUpdate = !UserScrolling && (lastExtent == null || Precision.AlmostBigger(ScrollableExtent, lastExtent.Value));
+
+                if (requiresScrollUpdate)
+                {
+                    // Schedule required to allow FillFlow to be the correct size.
+                    Schedule(() =>
+                    {
+                        if (!UserScrolling)
+                        {
+                            ScrollToEnd();
+                            lastExtent = ScrollableExtent;
+                        }
+                    });
+                }
+            }
+        }
     }
 }

osu.Game/Overlays/Mods/ModSection.cs

@@ -11,31 +11,30 @@ using System;
 using System.Linq;
 using System.Collections.Generic;
 using System.Threading;
+using Humanizer;
 using osu.Framework.Input.Events;
 using osu.Game.Graphics;
 
 namespace osu.Game.Overlays.Mods
 {
-    public abstract class ModSection : Container
+    public class ModSection : CompositeDrawable
     {
-        private readonly OsuSpriteText headerLabel;
+        private readonly Drawable header;
 
         public FillFlowContainer<ModButtonEmpty> ButtonsContainer { get; }
 
         public Action<Mod> Action;
-        protected abstract Key[] ToggleKeys { get; }
-        public abstract ModType ModType { get; }
 
-        public string Header
+        public Key[] ToggleKeys;
-        {
+
-            get => headerLabel.Text;
+        public readonly ModType ModType;
-            set => headerLabel.Text = value;
-        }
 
         public IEnumerable<Mod> SelectedMods => buttons.Select(b => b.SelectedMod).Where(m => m != null);
 
         private CancellationTokenSource modsLoadCts;
 
+        protected bool SelectionAnimationRunning => pendingSelectionOperations.Count > 0;
+
         /// <summary>
         /// True when all mod icons have completed loading.
         /// </summary>
@@ -52,7 +51,11 @@ namespace osu.Game.Overlays.Mods
 
                     return new ModButton(m)
                     {
-                        SelectionChanged = Action,
+                        SelectionChanged = mod =>
+                        {
+                            ModButtonStateChanged(mod);
+                            Action?.Invoke(mod);
+                        },
                     };
                 }).ToArray();
 
@@ -61,7 +64,7 @@ namespace osu.Game.Overlays.Mods
                 if (modContainers.Length == 0)
                 {
                     ModIconsLoaded = true;
-                    headerLabel.Hide();
+                    header.Hide();
                     Hide();
                     return;
                 }
@@ -76,11 +79,15 @@ namespace osu.Game.Overlays.Mods
 
                 buttons = modContainers.OfType<ModButton>().ToArray();
 
-                headerLabel.FadeIn(200);
+                header.FadeIn(200);
                 this.FadeIn(200);
             }
         }
 
+        protected virtual void ModButtonStateChanged(Mod mod)
+        {
+        }
+
         private ModButton[] buttons = Array.Empty<ModButton>();
 
         protected override bool OnKeyDown(KeyDownEvent e)
@@ -97,30 +104,75 @@ namespace osu.Game.Overlays.Mods
             return base.OnKeyDown(e);
         }
 
-        public void DeselectAll() => DeselectTypes(buttons.Select(b => b.SelectedMod?.GetType()).Where(t => t != null));
+        private const double initial_multiple_selection_delay = 120;
+
+        private double selectionDelay = initial_multiple_selection_delay;
+        private double lastSelection;
+
+        private readonly Queue<Action> pendingSelectionOperations = new Queue<Action>();
+
+        protected override void Update()
+        {
+            base.Update();
+
+            if (selectionDelay == initial_multiple_selection_delay || Time.Current - lastSelection >= selectionDelay)
+            {
+                if (pendingSelectionOperations.TryDequeue(out var dequeuedAction))
+                {
+                    dequeuedAction();
+
+                    // each time we play an animation, we decrease the time until the next animation (to ramp the visual and audible elements).
+                    selectionDelay = Math.Max(30, selectionDelay * 0.8f);
+                    lastSelection = Time.Current;
+                }
+                else
+                {
+                    // reset the selection delay after all animations have been completed.
+                    // this will cause the next action to be immediately performed.
+                    selectionDelay = initial_multiple_selection_delay;
+                }
+            }
+        }
+
+        /// <summary>
+        /// Selects all mods.
+        /// </summary>
+        public void SelectAll()
+        {
+            pendingSelectionOperations.Clear();
+
+            foreach (var button in buttons.Where(b => !b.Selected))
+                pendingSelectionOperations.Enqueue(() => button.SelectAt(0));
+        }
+
+        /// <summary>
+        /// Deselects all mods.
+        /// </summary>
+        public void DeselectAll()
+        {
+            pendingSelectionOperations.Clear();
+            DeselectTypes(buttons.Select(b => b.SelectedMod?.GetType()).Where(t => t != null));
+        }
 
         /// <summary>
         /// Deselect one or more mods in this section.
         /// </summary>
         /// <param name="modTypes">The types of <see cref="Mod"/>s which should be deselected.</param>
-        /// <param name="immediate">Set to true to bypass animations and update selections immediately.</param>
+        /// <param name="immediate">Whether the deselection should happen immediately. Should only be used when required to ensure correct selection flow.</param>
         public void DeselectTypes(IEnumerable<Type> modTypes, bool immediate = false)
         {
-            int delay = 0;
-
             foreach (var button in buttons)
             {
-                Mod selected = button.SelectedMod;
+                if (button.SelectedMod == null) continue;
-                if (selected == null) continue;
 
                 foreach (var type in modTypes)
                 {
-                    if (type.IsInstanceOfType(selected))
+                    if (type.IsInstanceOfType(button.SelectedMod))
                     {
                         if (immediate)
                             button.Deselect();
                         else
-                            Scheduler.AddDelayed(button.Deselect, delay += 50);
+                            pendingSelectionOperations.Enqueue(button.Deselect);
                     }
                 }
             }
@@ -130,13 +182,13 @@ namespace osu.Game.Overlays.Mods
         /// Updates all buttons with the given list of selected mods.
         /// </summary>
         /// <param name="newSelectedMods">The new list of selected mods to select.</param>
-        public void UpdateSelectedMods(IReadOnlyList<Mod> newSelectedMods)
+        public void UpdateSelectedButtons(IReadOnlyList<Mod> newSelectedMods)
         {
             foreach (var button in buttons)
-                updateButtonMods(button, newSelectedMods);
+                updateButtonSelection(button, newSelectedMods);
         }
 
-        private void updateButtonMods(ModButton button, IReadOnlyList<Mod> newSelectedMods)
+        private void updateButtonSelection(ModButton button, IReadOnlyList<Mod> newSelectedMods)
         {
             foreach (var mod in newSelectedMods)
             {
@@ -153,23 +205,19 @@ namespace osu.Game.Overlays.Mods
             button.Deselect();
         }
 
-        protected ModSection()
+        public ModSection(ModType type)
         {
+            ModType = type;
+
             AutoSizeAxes = Axes.Y;
             RelativeSizeAxes = Axes.X;
 
             Origin = Anchor.TopCentre;
             Anchor = Anchor.TopCentre;
 
-            Children = new Drawable[]
+            InternalChildren = new[]
             {
-                headerLabel = new OsuSpriteText
+                header = CreateHeader(type.Humanize(LetterCasing.Title)),
-                {
-                    Origin = Anchor.TopLeft,
-                    Anchor = Anchor.TopLeft,
-                    Position = new Vector2(0f, 0f),
-                    Font = OsuFont.GetFont(weight: FontWeight.Bold)
-                },
                 ButtonsContainer = new FillFlowContainer<ModButtonEmpty>
                 {
                     AutoSizeAxes = Axes.Y,
@@ -185,5 +233,20 @@ namespace osu.Game.Overlays.Mods
                 },
             };
         }
+
+        protected virtual Drawable CreateHeader(string text) => new OsuSpriteText
+        {
+            Font = OsuFont.GetFont(weight: FontWeight.Bold),
+            Text = text
+        };
+
+        /// <summary>
+        /// Play out all remaining animations immediately to leave mods in a good (final) state.
+        /// </summary>
+        public void FlushAnimation()
+        {
+            while (pendingSelectionOperations.TryDequeue(out var dequeuedAction))
+                dequeuedAction();
+        }
     }
 }

osu.Game/Overlays/Mods/ModSelectOverlay.cs

@@ -4,6 +4,7 @@
 using System;
 using System.Collections.Generic;
 using System.Linq;
+using JetBrains.Annotations;
 using osu.Framework.Allocation;
 using osu.Framework.Audio;
 using osu.Framework.Audio.Sample;
@@ -19,30 +20,54 @@ using osu.Game.Graphics.Containers;
 using osu.Game.Graphics.Sprites;
 using osu.Game.Graphics.UserInterface;
 using osu.Game.Input.Bindings;
-using osu.Game.Overlays.Mods.Sections;
 using osu.Game.Rulesets.Mods;
 using osu.Game.Screens;
+using osu.Game.Utils;
 using osuTK;
 using osuTK.Graphics;
 using osuTK.Input;
 
 namespace osu.Game.Overlays.Mods
 {
-    public class ModSelectOverlay : WaveOverlayContainer
+    public abstract class ModSelectOverlay : WaveOverlayContainer
     {
-        private readonly Func<Mod, bool> isValidMod;
         public const float HEIGHT = 510;
 
         protected readonly TriangleButton DeselectAllButton;
         protected readonly TriangleButton CustomiseButton;
         protected readonly TriangleButton CloseButton;
 
+        protected readonly Drawable MultiplierSection;
         protected readonly OsuSpriteText MultiplierLabel;
 
+        protected readonly FillFlowContainer FooterContainer;
+
         protected override bool BlockNonPositionalInput => false;
 
         protected override bool DimMainContent => false;
 
+        /// <summary>
+        /// Whether <see cref="Mod"/>s underneath the same <see cref="MultiMod"/> instance should appear as stacked buttons.
+        /// </summary>
+        protected virtual bool Stacked => true;
+
+        [NotNull]
+        private Func<Mod, bool> isValidMod = m => true;
+
+        /// <summary>
+        /// A function that checks whether a given mod is selectable.
+        /// </summary>
+        [NotNull]
+        public Func<Mod, bool> IsValidMod
+        {
+            get => isValidMod;
+            set
+            {
+                isValidMod = value ?? throw new ArgumentNullException(nameof(value));
+                updateAvailableMods();
+            }
+        }
+
         protected readonly FillFlowContainer<ModSection> ModSectionsContainer;
 
         protected readonly ModSettingsContainer ModSettingsContainer;
@@ -57,14 +82,10 @@ namespace osu.Game.Overlays.Mods
         private const float content_width = 0.8f;
         private const float footer_button_spacing = 20;
 
-        private readonly FillFlowContainer footerContainer;
-
         private SampleChannel sampleOn, sampleOff;
 
-        public ModSelectOverlay(Func<Mod, bool> isValidMod = null)
+        protected ModSelectOverlay()
         {
-            this.isValidMod = isValidMod ?? (m => true);
-
             Waves.FirstWaveColour = Color4Extensions.FromHex(@"19b0e2");
             Waves.SecondWaveColour = Color4Extensions.FromHex(@"2280a2");
             Waves.ThirdWaveColour = Color4Extensions.FromHex(@"005774");
@@ -190,13 +211,31 @@ namespace osu.Game.Overlays.Mods
                                                 Width = content_width,
                                                 LayoutDuration = 200,
                                                 LayoutEasing = Easing.OutQuint,
-                                                Children = new ModSection[]
+                                                Children = new[]
                                                 {
-                                                    new DifficultyReductionSection { Action = modButtonPressed },
+                                                    CreateModSection(ModType.DifficultyReduction).With(s =>
-                                                    new DifficultyIncreaseSection { Action = modButtonPressed },
+                                                    {
-                                                    new AutomationSection { Action = modButtonPressed },
+                                                        s.ToggleKeys = new[] { Key.Q, Key.W, Key.E, Key.R, Key.T, Key.Y, Key.U, Key.I, Key.O, Key.P };
-                                                    new ConversionSection { Action = modButtonPressed },
+                                                        s.Action = modButtonPressed;
-                                                    new FunSection { Action = modButtonPressed },
+                                                    }),
+                                                    CreateModSection(ModType.DifficultyIncrease).With(s =>
+                                                    {
+                                                        s.ToggleKeys = new[] { Key.A, Key.S, Key.D, Key.F, Key.G, Key.H, Key.J, Key.K, Key.L };
+                                                        s.Action = modButtonPressed;
+                                                    }),
+                                                    CreateModSection(ModType.Automation).With(s =>
+                                                    {
+                                                        s.ToggleKeys = new[] { Key.Z, Key.X, Key.C, Key.V, Key.B, Key.N, Key.M };
+                                                        s.Action = modButtonPressed;
+                                                    }),
+                                                    CreateModSection(ModType.Conversion).With(s =>
+                                                    {
+                                                        s.Action = modButtonPressed;
+                                                    }),
+                                                    CreateModSection(ModType.Fun).With(s =>
+                                                    {
+                                                        s.Action = modButtonPressed;
+                                                    }),
                                                 }
                                             },
                                         }
@@ -231,7 +270,7 @@ namespace osu.Game.Overlays.Mods
                                         Colour = new Color4(172, 20, 116, 255),
                                         Alpha = 0.5f,
                                     },
-                                    footerContainer = new FillFlowContainer
+                                    FooterContainer = new FillFlowContainer
                                     {
                                         Origin = Anchor.BottomCentre,
                                         Anchor = Anchor.BottomCentre,
@@ -245,7 +284,7 @@ namespace osu.Game.Overlays.Mods
                                             Vertical = 15,
                                             Horizontal = OsuScreen.HORIZONTAL_OVERFLOW_PADDING
                                         },
-                                        Children = new Drawable[]
+                                        Children = new[]
                                         {
                                             DeselectAllButton = new TriangleButton
                                             {
@@ -272,7 +311,7 @@ namespace osu.Game.Overlays.Mods
                                                 Origin = Anchor.CentreLeft,
                                                 Anchor = Anchor.CentreLeft,
                                             },
-                                            new FillFlowContainer
+                                            MultiplierSection = new FillFlowContainer
                                             {
                                                 AutoSizeAxes = Axes.Both,
                                                 Spacing = new Vector2(footer_button_spacing / 2, 0),
@@ -328,33 +367,25 @@ namespace osu.Game.Overlays.Mods
             refreshSelectedMods();
         }
 
-        /// <summary>
-        /// Deselect one or more mods.
-        /// </summary>
-        /// <param name="modTypes">The types of <see cref="Mod"/>s which should be deselected.</param>
-        /// <param name="immediate">Set to true to bypass animations and update selections immediately.</param>
-        private void deselectTypes(Type[] modTypes, bool immediate = false)
-        {
-            if (modTypes.Length == 0) return;
-
-            foreach (var section in ModSectionsContainer.Children)
-                section.DeselectTypes(modTypes, immediate);
-        }
-
         protected override void LoadComplete()
         {
             base.LoadComplete();
 
-            availableMods.BindValueChanged(availableModsChanged, true);
+            availableMods.BindValueChanged(_ => updateAvailableMods(), true);
-            SelectedMods.BindValueChanged(selectedModsChanged, true);
+            SelectedMods.BindValueChanged(_ => updateSelectedButtons(), true);
         }
 
         protected override void PopOut()
         {
             base.PopOut();
 
-            footerContainer.MoveToX(content_width, WaveContainer.DISAPPEAR_DURATION, Easing.InSine);
+            foreach (var section in ModSectionsContainer)
-            footerContainer.FadeOut(WaveContainer.DISAPPEAR_DURATION, Easing.InSine);
+            {
+                section.FlushAnimation();
+            }
+
+            FooterContainer.MoveToX(content_width, WaveContainer.DISAPPEAR_DURATION, Easing.InSine);
+            FooterContainer.FadeOut(WaveContainer.DISAPPEAR_DURATION, Easing.InSine);
 
             foreach (var section in ModSectionsContainer.Children)
             {
@@ -368,8 +399,8 @@ namespace osu.Game.Overlays.Mods
         {
             base.PopIn();
 
-            footerContainer.MoveToX(0, WaveContainer.APPEAR_DURATION, Easing.OutQuint);
+            FooterContainer.MoveToX(0, WaveContainer.APPEAR_DURATION, Easing.OutQuint);
-            footerContainer.FadeIn(WaveContainer.APPEAR_DURATION, Easing.OutQuint);
+            FooterContainer.FadeIn(WaveContainer.APPEAR_DURATION, Easing.OutQuint);
 
             foreach (var section in ModSectionsContainer.Children)
             {
@@ -400,18 +431,53 @@ namespace osu.Game.Overlays.Mods
 
         public override bool OnPressed(GlobalAction action) => false; // handled by back button
 
-        private void availableModsChanged(ValueChangedEvent<Dictionary<ModType, IReadOnlyList<Mod>>> mods)
+        private void updateAvailableMods()
         {
-            if (mods.NewValue == null) return;
+            if (availableMods?.Value == null)
+                return;
 
             foreach (var section in ModSectionsContainer.Children)
-                section.Mods = mods.NewValue[section.ModType].Where(isValidMod);
+            {
+                IEnumerable<Mod> modEnumeration = availableMods.Value[section.ModType];
+
+                if (!Stacked)
+                    modEnumeration = ModUtils.FlattenMods(modEnumeration);
+
+                section.Mods = modEnumeration.Select(getValidModOrNull).Where(m => m != null);
             }
 
-        private void selectedModsChanged(ValueChangedEvent<IReadOnlyList<Mod>> mods)
+            updateSelectedButtons();
+        }
+
+        /// <summary>
+        /// Returns a valid form of a given <see cref="Mod"/> if possible, or null otherwise.
+        /// </summary>
+        /// <remarks>
+        /// This is a recursive process during which any invalid mods are culled while preserving <see cref="MultiMod"/> structures where possible.
+        /// </remarks>
+        /// <param name="mod">The <see cref="Mod"/> to check.</param>
+        /// <returns>A valid form of <paramref name="mod"/> if exists, or null otherwise.</returns>
+        [CanBeNull]
+        private Mod getValidModOrNull([NotNull] Mod mod)
         {
+            if (!(mod is MultiMod multi))
+                return IsValidMod(mod) ? mod : null;
+
+            var validSubset = multi.Mods.Select(getValidModOrNull).Where(m => m != null).ToArray();
+
+            if (validSubset.Length == 0)
+                return null;
+
+            return validSubset.Length == 1 ? validSubset[0] : new MultiMod(validSubset);
+        }
+
+        private void updateSelectedButtons()
+        {
+            // Enumeration below may update the bindable list.
+            var selectedMods = SelectedMods.Value.ToList();
+
             foreach (var section in ModSectionsContainer.Children)
-                section.UpdateSelectedMods(mods.NewValue);
+                section.UpdateSelectedButtons(selectedMods);
 
             updateMods();
         }
@@ -438,22 +504,42 @@ namespace osu.Game.Overlays.Mods
         {
             if (selectedMod != null)
             {
-                if (State.Value == Visibility.Visible) sampleOn?.Play();
+                if (State.Value == Visibility.Visible)
+                    Scheduler.AddOnce(playSelectedSound);
 
-                deselectTypes(selectedMod.IncompatibleMods, true);
+                OnModSelected(selectedMod);
 
                 if (selectedMod.RequiresConfiguration) ModSettingsContainer.Show();
             }
             else
             {
-                if (State.Value == Visibility.Visible) sampleOff?.Play();
+                if (State.Value == Visibility.Visible)
+                    Scheduler.AddOnce(playDeselectedSound);
             }
 
             refreshSelectedMods();
         }
 
+        private void playSelectedSound() => sampleOn?.Play();
+        private void playDeselectedSound() => sampleOff?.Play();
+
+        /// <summary>
+        /// Invoked when a new <see cref="Mod"/> has been selected.
+        /// </summary>
+        /// <param name="mod">The <see cref="Mod"/> that has been selected.</param>
+        protected virtual void OnModSelected(Mod mod)
+        {
+        }
+
         private void refreshSelectedMods() => SelectedMods.Value = ModSectionsContainer.Children.SelectMany(s => s.SelectedMods).ToArray();
 
+        /// <summary>
+        /// Creates a <see cref="ModSection"/> that groups <see cref="Mod"/>s with the same <see cref="ModType"/>.
+        /// </summary>
+        /// <param name="type">The <see cref="ModType"/> of <see cref="Mod"/>s in the section.</param>
+        /// <returns>The <see cref="ModSection"/>.</returns>
+        protected virtual ModSection CreateModSection(ModType type) => new ModSection(type);
+
         #region Disposal
 
         protected override void Dispose(bool isDisposing)

osu.Game/Overlays/Mods/Sections/AutomationSection.cs

@@ -1,19 +0,0 @@
-// Copyright (c) ppy Pty Ltd <contact@ppy.sh>. Licensed under the MIT Licence.
-// See the LICENCE file in the repository root for full licence text.
-
-using osu.Game.Rulesets.Mods;
-using osuTK.Input;
-
-namespace osu.Game.Overlays.Mods.Sections
-{
-    public class AutomationSection : ModSection
-    {
-        protected override Key[] ToggleKeys => new[] { Key.Z, Key.X, Key.C, Key.V, Key.B, Key.N, Key.M };
-        public override ModType ModType => ModType.Automation;
-
-        public AutomationSection()
-        {
-            Header = @"Automation";
-        }
-    }
-}

osu.Game/Overlays/Mods/Sections/ConversionSection.cs

@@ -1,19 +0,0 @@
-// Copyright (c) ppy Pty Ltd <contact@ppy.sh>. Licensed under the MIT Licence.
-// See the LICENCE file in the repository root for full licence text.
-
-using osu.Game.Rulesets.Mods;
-using osuTK.Input;
-
-namespace osu.Game.Overlays.Mods.Sections
-{
-    public class ConversionSection : ModSection
-    {
-        protected override Key[] ToggleKeys => null;
-        public override ModType ModType => ModType.Conversion;
-
-        public ConversionSection()
-        {
-            Header = @"Conversion";
-        }
-    }
-}

osu.Game/Overlays/Mods/Sections/DifficultyIncreaseSection.cs

@@ -1,19 +0,0 @@
-// Copyright (c) ppy Pty Ltd <contact@ppy.sh>. Licensed under the MIT Licence.
-// See the LICENCE file in the repository root for full licence text.
-
-using osu.Game.Rulesets.Mods;
-using osuTK.Input;
-
-namespace osu.Game.Overlays.Mods.Sections
-{
-    public class DifficultyIncreaseSection : ModSection
-    {
-        protected override Key[] ToggleKeys => new[] { Key.A, Key.S, Key.D, Key.F, Key.G, Key.H, Key.J, Key.K, Key.L };
-        public override ModType ModType => ModType.DifficultyIncrease;
-
-        public DifficultyIncreaseSection()
-        {
-            Header = @"Difficulty Increase";
-        }
-    }
-}

osu.Game/Overlays/Mods/Sections/DifficultyReductionSection.cs

@@ -1,19 +0,0 @@
-// Copyright (c) ppy Pty Ltd <contact@ppy.sh>. Licensed under the MIT Licence.
-// See the LICENCE file in the repository root for full licence text.
-
-using osu.Game.Rulesets.Mods;
-using osuTK.Input;
-
-namespace osu.Game.Overlays.Mods.Sections
-{
-    public class DifficultyReductionSection : ModSection
-    {
-        protected override Key[] ToggleKeys => new[] { Key.Q, Key.W, Key.E, Key.R, Key.T, Key.Y, Key.U, Key.I, Key.O, Key.P };
-        public override ModType ModType => ModType.DifficultyReduction;
-
-        public DifficultyReductionSection()
-        {
-            Header = @"Difficulty Reduction";
-        }
-    }
-}

osu.Game/Overlays/Mods/Sections/FunSection.cs

@@ -1,19 +0,0 @@
-// Copyright (c) ppy Pty Ltd <contact@ppy.sh>. Licensed under the MIT Licence.
-// See the LICENCE file in the repository root for full licence text.
-
-using osu.Game.Rulesets.Mods;
-using osuTK.Input;
-
-namespace osu.Game.Overlays.Mods.Sections
-{
-    public class FunSection : ModSection
-    {
-        protected override Key[] ToggleKeys => null;
-        public override ModType ModType => ModType.Fun;
-
-        public FunSection()
-        {
-            Header = @"Fun";
-        }
-    }
-}

osu.Game/Overlays/Mods/SoloModSelectOverlay.cs

@@ -0,0 +1,18 @@
+// Copyright (c) ppy Pty Ltd <contact@ppy.sh>. Licensed under the MIT Licence.
+// See the LICENCE file in the repository root for full licence text.
+
+using osu.Game.Rulesets.Mods;
+
+namespace osu.Game.Overlays.Mods
+{
+    public class SoloModSelectOverlay : ModSelectOverlay
+    {
+        protected override void OnModSelected(Mod mod)
+        {
+            base.OnModSelected(mod);
+
+            foreach (var section in ModSectionsContainer.Children)
+                section.DeselectTypes(mod.IncompatibleMods, true);
+        }
+    }
+}

osu.Game/Rulesets/UI/ModIcon.cs

@@ -29,8 +29,6 @@ namespace osu.Game.Rulesets.UI
 
         private const float size = 80;
 
-        private readonly ModType type;
-
         public virtual string TooltipText => showTooltip ? mod.IconTooltip : null;
 
         private Mod mod;
@@ -42,10 +40,18 @@ namespace osu.Game.Rulesets.UI
             set
             {
                 mod = value;
+
+                if (IsLoaded)
                     updateMod(value);
             }
         }
 
+        [Resolved]
+        private OsuColour colours { get; set; }
+
+        private Color4 backgroundColour;
+        private Color4 highlightedColour;
+
         /// <summary>
         /// Construct a new instance.
         /// </summary>
@@ -56,8 +62,6 @@ namespace osu.Game.Rulesets.UI
             this.mod = mod ?? throw new ArgumentNullException(nameof(mod));
             this.showTooltip = showTooltip;
 
-            type = mod.Type;
-
             Size = new Vector2(size);
 
             Children = new Drawable[]
@@ -89,6 +93,13 @@ namespace osu.Game.Rulesets.UI
                     Icon = FontAwesome.Solid.Question
                 },
             };
+        }
+
+        protected override void LoadComplete()
+        {
+            base.LoadComplete();
+
+            Selected.BindValueChanged(_ => updateColour());
 
             updateMod(mod);
         }
@@ -102,20 +113,14 @@ namespace osu.Game.Rulesets.UI
             {
                 modIcon.FadeOut();
                 modAcronym.FadeIn();
-                return;
             }
-
+            else
+            {
                 modIcon.FadeIn();
                 modAcronym.FadeOut();
             }
 
-        private Color4 backgroundColour;
+            switch (value.Type)
-        private Color4 highlightedColour;
-
-        [BackgroundDependencyLoader]
-        private void load(OsuColour colours)
-        {
-            switch (type)
             {
                 default:
                 case ModType.DifficultyIncrease:
@@ -149,12 +154,13 @@ namespace osu.Game.Rulesets.UI
                     modIcon.Colour = colours.Yellow;
                     break;
             }
+
+            updateColour();
         }
 
-        protected override void LoadComplete()
+        private void updateColour()
         {
-            base.LoadComplete();
+            background.Colour = Selected.Value ? highlightedColour : backgroundColour;
-            Selected.BindValueChanged(selected => background.Colour = selected.NewValue ? highlightedColour : backgroundColour, true);
         }
     }
 }

osu.Game/Rulesets/UI/Scrolling/DrawableScrollingRuleset.cs

@@ -91,7 +91,11 @@ namespace osu.Game.Rulesets.UI.Scrolling
             scrollingInfo = new LocalScrollingInfo();
             scrollingInfo.Direction.BindTo(Direction);
             scrollingInfo.TimeRange.BindTo(TimeRange);
+        }
 
+        [BackgroundDependencyLoader]
+        private void load()
+        {
             switch (VisualisationMethod)
             {
                 case ScrollVisualisationMethod.Sequential:
@@ -106,11 +110,7 @@ namespace osu.Game.Rulesets.UI.Scrolling
                     scrollingInfo.Algorithm = new ConstantScrollAlgorithm();
                     break;
             }
-        }
 
-        [BackgroundDependencyLoader]
-        private void load()
-        {
             double lastObjectTime = Objects.LastOrDefault()?.GetEndTime() ?? double.MaxValue;
             double baseBeatLength = TimingControlPoint.DEFAULT_BEAT_LENGTH;
 

osu.Game/Screens/OnlinePlay/Components/ReadyButton.cs

@@ -1,77 +1,29 @@
 // Copyright (c) ppy Pty Ltd <contact@ppy.sh>. Licensed under the MIT Licence.
 // See the LICENCE file in the repository root for full licence text.
 
-using System;
 using osu.Framework.Allocation;
 using osu.Framework.Bindables;
-using osu.Game.Beatmaps;
-using osu.Game.Graphics;
 using osu.Game.Graphics.UserInterface;
+using osu.Game.Online;
 using osu.Game.Online.Rooms;
 
 namespace osu.Game.Screens.OnlinePlay.Components
 {
     public abstract class ReadyButton : TriangleButton
     {
-        public readonly Bindable<PlaylistItem> SelectedItem = new Bindable<PlaylistItem>();
-
         public new readonly BindableBool Enabled = new BindableBool();
 
-        [Resolved]
+        private IBindable<BeatmapAvailability> availability;
-        protected IBindable<WorkingBeatmap> GameBeatmap { get; private set; }
-
-        [Resolved]
-        private BeatmapManager beatmaps { get; set; }
-
-        private bool hasBeatmap;
-
-        private IBindable<WeakReference<BeatmapSetInfo>> managerUpdated;
-        private IBindable<WeakReference<BeatmapSetInfo>> managerRemoved;
 
         [BackgroundDependencyLoader]
-        private void load(OsuColour colours)
+        private void load(OnlinePlayBeatmapAvailablilityTracker beatmapTracker)
         {
-            managerUpdated = beatmaps.ItemUpdated.GetBoundCopy();
+            availability = beatmapTracker.Availability.GetBoundCopy();
-            managerUpdated.BindValueChanged(beatmapUpdated);
-            managerRemoved = beatmaps.ItemRemoved.GetBoundCopy();
-            managerRemoved.BindValueChanged(beatmapRemoved);
 
-            SelectedItem.BindValueChanged(item => updateSelectedItem(item.NewValue), true);
+            availability.BindValueChanged(_ => updateState());
+            Enabled.BindValueChanged(_ => updateState(), true);
         }
 
-        private void updateSelectedItem(PlaylistItem _) => Scheduler.AddOnce(updateBeatmapState);
+        private void updateState() => base.Enabled.Value = availability.Value.State == DownloadState.LocallyAvailable && Enabled.Value;
-        private void beatmapUpdated(ValueChangedEvent<WeakReference<BeatmapSetInfo>> _) => Scheduler.AddOnce(updateBeatmapState);
-        private void beatmapRemoved(ValueChangedEvent<WeakReference<BeatmapSetInfo>> _) => Scheduler.AddOnce(updateBeatmapState);
-
-        private void updateBeatmapState()
-        {
-            int? beatmapId = SelectedItem.Value?.Beatmap.Value?.OnlineBeatmapID;
-            string checksum = SelectedItem.Value?.Beatmap.Value?.MD5Hash;
-
-            if (beatmapId == null || checksum == null)
-                return;
-
-            var databasedBeatmap = beatmaps.QueryBeatmap(b => b.OnlineBeatmapID == beatmapId && b.MD5Hash == checksum);
-
-            hasBeatmap = databasedBeatmap?.BeatmapSet?.DeletePending == false;
-        }
-
-        protected override void Update()
-        {
-            base.Update();
-
-            updateEnabledState();
-        }
-
-        private void updateEnabledState()
-        {
-            if (GameBeatmap.Value == null || SelectedItem.Value == null)
-            {
-                base.Enabled.Value = false;
-                return;
-            }
-
-            base.Enabled.Value = hasBeatmap && Enabled.Value;
-        }
     }
 }

osu.Game/Screens/OnlinePlay/DrawableRoomPlaylistItem.cs

@@ -124,7 +124,11 @@ namespace osu.Game.Screens.OnlinePlay
             modDisplay.Current.Value = requiredMods.ToArray();
         }
 
-        protected override Drawable CreateContent() => maskingContainer = new Container
+        protected override Drawable CreateContent()
+        {
+            Action<SpriteText> fontParameters = s => s.Font = OsuFont.Default.With(weight: FontWeight.SemiBold);
+
+            return maskingContainer = new Container
             {
                 RelativeSizeAxes = Axes.X,
                 Height = 50,
@@ -165,7 +169,7 @@ namespace osu.Game.Screens.OnlinePlay
                                 Direction = FillDirection.Vertical,
                                 Children = new Drawable[]
                                 {
-                                beatmapText = new LinkFlowContainer { AutoSizeAxes = Axes.Both },
+                                    beatmapText = new LinkFlowContainer(fontParameters) { AutoSizeAxes = Axes.Both },
                                     new FillFlowContainer
                                     {
                                         AutoSizeAxes = Axes.Both,
@@ -180,7 +184,7 @@ namespace osu.Game.Screens.OnlinePlay
                                                 Spacing = new Vector2(10f, 0),
                                                 Children = new Drawable[]
                                                 {
-                                                authorText = new LinkFlowContainer { AutoSizeAxes = Axes.Both },
+                                                    authorText = new LinkFlowContainer(fontParameters) { AutoSizeAxes = Axes.Both },
                                                     explicitContentPill = new ExplicitContentBeatmapPill
                                                     {
                                                         Alpha = 0f,
@@ -214,11 +218,17 @@ namespace osu.Game.Screens.OnlinePlay
                         Origin = Anchor.CentreRight,
                         Direction = FillDirection.Horizontal,
                         AutoSizeAxes = Axes.Both,
-                    X = -18,
+                        Spacing = new Vector2(5),
-                    ChildrenEnumerable = CreateButtons()
+                        X = -10,
+                        ChildrenEnumerable = CreateButtons().Select(button => button.With(b =>
+                        {
+                            b.Anchor = Anchor.Centre;
+                            b.Origin = Anchor.Centre;
+                        }))
                     }
                 }
             };
+        }
 
         protected virtual IEnumerable<Drawable> CreateButtons() =>
             new Drawable[]
@@ -227,14 +237,29 @@ namespace osu.Game.Screens.OnlinePlay
                 {
                     Size = new Vector2(50, 30)
                 },
-                new IconButton
+                new PlaylistRemoveButton
                 {
-                    Icon = FontAwesome.Solid.MinusSquare,
+                    Size = new Vector2(30, 30),
                     Alpha = allowEdit ? 1 : 0,
                     Action = () => RequestDeletion?.Invoke(Model),
                 },
             };
 
+        public class PlaylistRemoveButton : GrayButton
+        {
+            public PlaylistRemoveButton()
+                : base(FontAwesome.Solid.MinusSquare)
+            {
+                TooltipText = "Remove from playlist";
+            }
+
+            [BackgroundDependencyLoader]
+            private void load()
+            {
+                Icon.Scale = new Vector2(0.8f);
+            }
+        }
+
         protected override bool OnClick(ClickEvent e)
         {
             if (allowSelection)
@@ -318,24 +343,18 @@ namespace osu.Game.Screens.OnlinePlay
                                 Colour = Color4.Black,
                                 Width = 0.4f,
                             },
-                            // Piecewise-linear gradient with 3 segments to make it appear smoother
+                            // Piecewise-linear gradient with 2 segments to make it appear smoother
                             new Box
                             {
                                 RelativeSizeAxes = Axes.Both,
-                                Colour = ColourInfo.GradientHorizontal(Color4.Black, new Color4(0f, 0f, 0f, 0.9f)),
+                                Colour = ColourInfo.GradientHorizontal(Color4.Black, new Color4(0f, 0f, 0f, 0.7f)),
-                                Width = 0.05f,
+                                Width = 0.4f,
                             },
                             new Box
                             {
                                 RelativeSizeAxes = Axes.Both,
-                                Colour = ColourInfo.GradientHorizontal(new Color4(0f, 0f, 0f, 0.9f), new Color4(0f, 0f, 0f, 0.1f)),
+                                Colour = ColourInfo.GradientHorizontal(new Color4(0f, 0f, 0f, 0.7f), new Color4(0, 0, 0, 0.4f)),
-                                Width = 0.2f,
+                                Width = 0.4f,
-                            },
-                            new Box
-                            {
-                                RelativeSizeAxes = Axes.Both,
-                                Colour = ColourInfo.GradientHorizontal(new Color4(0f, 0f, 0f, 0.1f), new Color4(0, 0, 0, 0)),
-                                Width = 0.05f,
                             },
                         }
                     }

osu.Game/Screens/OnlinePlay/FooterButtonFreeMods.cs

@@ -0,0 +1,63 @@
+// Copyright (c) ppy Pty Ltd <contact@ppy.sh>. Licensed under the MIT Licence.
+// See the LICENCE file in the repository root for full licence text.
+
+using System.Collections.Generic;
+using osu.Framework.Allocation;
+using osu.Framework.Bindables;
+using osu.Framework.Extensions.Color4Extensions;
+using osu.Framework.Graphics;
+using osu.Framework.Graphics.UserInterface;
+using osu.Game.Graphics;
+using osu.Game.Rulesets.Mods;
+using osu.Game.Screens.Play.HUD;
+using osu.Game.Screens.Select;
+using osuTK;
+
+namespace osu.Game.Screens.OnlinePlay
+{
+    public class FooterButtonFreeMods : FooterButton, IHasCurrentValue<IReadOnlyList<Mod>>
+    {
+        public Bindable<IReadOnlyList<Mod>> Current
+        {
+            get => modDisplay.Current;
+            set => modDisplay.Current = value;
+        }
+
+        private readonly ModDisplay modDisplay;
+
+        public FooterButtonFreeMods()
+        {
+            ButtonContentContainer.Add(modDisplay = new ModDisplay
+            {
+                Anchor = Anchor.Centre,
+                Origin = Anchor.Centre,
+                DisplayUnrankedText = false,
+                Scale = new Vector2(0.8f),
+                ExpansionMode = ExpansionMode.AlwaysContracted,
+            });
+        }
+
+        [BackgroundDependencyLoader]
+        private void load(OsuColour colours)
+        {
+            SelectedColour = colours.Yellow;
+            DeselectedColour = SelectedColour.Opacity(0.5f);
+            Text = @"freemods";
+        }
+
+        protected override void LoadComplete()
+        {
+            base.LoadComplete();
+
+            Current.BindValueChanged(_ => updateModDisplay(), true);
+        }
+
+        private void updateModDisplay()
+        {
+            if (Current.Value?.Count > 0)
+                modDisplay.FadeIn();
+            else
+                modDisplay.FadeOut();
+        }
+    }
+}

osu.Game/Screens/OnlinePlay/FreeModSelectOverlay.cs

@@ -0,0 +1,145 @@
+// Copyright (c) ppy Pty Ltd <contact@ppy.sh>. Licensed under the MIT Licence.
+// See the LICENCE file in the repository root for full licence text.
+
+using System;
+using System.Linq;
+using osu.Framework.Graphics;
+using osu.Framework.Graphics.Containers;
+using osu.Framework.Graphics.Sprites;
+using osu.Game.Graphics;
+using osu.Game.Graphics.UserInterface;
+using osu.Game.Overlays.Mods;
+using osu.Game.Rulesets.Mods;
+
+namespace osu.Game.Screens.OnlinePlay
+{
+    /// <summary>
+    /// A <see cref="ModSelectOverlay"/> used for free-mod selection in online play.
+    /// </summary>
+    public class FreeModSelectOverlay : ModSelectOverlay
+    {
+        protected override bool Stacked => false;
+
+        public new Func<Mod, bool> IsValidMod
+        {
+            get => base.IsValidMod;
+            set => base.IsValidMod = m => m.HasImplementation && !m.RequiresConfiguration && !(m is ModAutoplay) && value(m);
+        }
+
+        public FreeModSelectOverlay()
+        {
+            IsValidMod = m => true;
+
+            CustomiseButton.Alpha = 0;
+            MultiplierSection.Alpha = 0;
+            DeselectAllButton.Alpha = 0;
+
+            Drawable selectAllButton;
+            Drawable deselectAllButton;
+
+            FooterContainer.AddRange(new[]
+            {
+                selectAllButton = new TriangleButton
+                {
+                    Origin = Anchor.CentreLeft,
+                    Anchor = Anchor.CentreLeft,
+                    Width = 180,
+                    Text = "Select All",
+                    Action = selectAll,
+                },
+                // Unlike the base mod select overlay, this button deselects mods instantaneously.
+                deselectAllButton = new TriangleButton
+                {
+                    Origin = Anchor.CentreLeft,
+                    Anchor = Anchor.CentreLeft,
+                    Width = 180,
+                    Text = "Deselect All",
+                    Action = deselectAll,
+                },
+            });
+
+            FooterContainer.SetLayoutPosition(selectAllButton, -2);
+            FooterContainer.SetLayoutPosition(deselectAllButton, -1);
+        }
+
+        private void selectAll()
+        {
+            foreach (var section in ModSectionsContainer.Children)
+                section.SelectAll();
+        }
+
+        private void deselectAll()
+        {
+            foreach (var section in ModSectionsContainer.Children)
+                section.DeselectAll();
+        }
+
+        protected override ModSection CreateModSection(ModType type) => new FreeModSection(type);
+
+        private class FreeModSection : ModSection
+        {
+            private HeaderCheckbox checkbox;
+
+            public FreeModSection(ModType type)
+                : base(type)
+            {
+            }
+
+            protected override Drawable CreateHeader(string text) => new Container
+            {
+                AutoSizeAxes = Axes.Y,
+                RelativeSizeAxes = Axes.X,
+                Child = checkbox = new HeaderCheckbox
+                {
+                    LabelText = text,
+                    Changed = onCheckboxChanged
+                }
+            };
+
+            private void onCheckboxChanged(bool value)
+            {
+                if (value)
+                    SelectAll();
+                else
+                    DeselectAll();
+            }
+
+            protected override void ModButtonStateChanged(Mod mod)
+            {
+                base.ModButtonStateChanged(mod);
+
+                if (!SelectionAnimationRunning)
+                {
+                    var validButtons = ButtonsContainer.OfType<ModButton>().Where(b => b.Mod.HasImplementation);
+                    checkbox.Current.Value = validButtons.All(b => b.Selected);
+                }
+            }
+        }
+
+        private class HeaderCheckbox : OsuCheckbox
+        {
+            public Action<bool> Changed;
+
+            protected override bool PlaySoundsOnUserChange => false;
+
+            public HeaderCheckbox()
+                : base(false)
+
+            {
+            }
+
+            protected override void ApplyLabelParameters(SpriteText text)
+            {
+                base.ApplyLabelParameters(text);
+
+                text.Font = OsuFont.GetFont(weight: FontWeight.Bold);
+            }
+
+            protected override void OnUserChange(bool value)
+            {
+                base.OnUserChange(value);
+                Changed?.Invoke(value);
+            }
+        }
+    }
+}

osu.Game/Screens/OnlinePlay/Match/Components/Footer.cs

@@ -3,13 +3,11 @@
 
 using System;
 using osu.Framework.Allocation;
-using osu.Framework.Bindables;
 using osu.Framework.Extensions.Color4Extensions;
 using osu.Framework.Graphics;
 using osu.Framework.Graphics.Containers;
 using osu.Framework.Graphics.Shapes;
 using osu.Game.Graphics;
-using osu.Game.Online.Rooms;
 using osu.Game.Screens.OnlinePlay.Playlists;
 using osuTK;
 
@@ -20,7 +18,6 @@ namespace osu.Game.Screens.OnlinePlay.Match.Components
         public const float HEIGHT = 50;
 
         public Action OnStart;
-        public readonly Bindable<PlaylistItem> SelectedItem = new Bindable<PlaylistItem>();
 
         private readonly Drawable background;
 
@@ -37,7 +34,6 @@ namespace osu.Game.Screens.OnlinePlay.Match.Components
                     Anchor = Anchor.Centre,
                     Origin = Anchor.Centre,
                     Size = new Vector2(600, 50),
-                    SelectedItem = { BindTarget = SelectedItem },
                     Action = () => OnStart?.Invoke()
                 }
             };

osu.Game/Screens/OnlinePlay/Match/RoomSubScreen.cs

@@ -2,6 +2,7 @@
 // See the LICENCE file in the repository root for full licence text.
 
 using System;
+using System.Collections.Generic;
 using System.Linq;
 using osu.Framework.Allocation;
 using osu.Framework.Audio;
@@ -29,6 +30,11 @@ namespace osu.Game.Screens.OnlinePlay.Match
         [Resolved(typeof(Room), nameof(Room.Playlist))]
         protected BindableList<PlaylistItem> Playlist { get; private set; }
 
+        /// <summary>
+        /// Any mods applied by/to the local user.
+        /// </summary>
+        protected readonly Bindable<IReadOnlyList<Mod>> UserMods = new Bindable<IReadOnlyList<Mod>>(Array.Empty<Mod>());
+
         [Resolved]
         private MusicController music { get; set; }
 
@@ -40,6 +46,20 @@ namespace osu.Game.Screens.OnlinePlay.Match
 
         private IBindable<WeakReference<BeatmapSetInfo>> managerUpdated;
 
+        [Cached]
+        protected OnlinePlayBeatmapAvailablilityTracker BeatmapAvailablilityTracker { get; }
+
+        protected RoomSubScreen()
+        {
+            AddInternal(BeatmapAvailablilityTracker = new OnlinePlayBeatmapAvailablilityTracker
+            {
+                SelectedItem = { BindTarget = SelectedItem }
+            });
+        }
+
+        protected override void ClearInternal(bool disposeChildren = true) =>
+            throw new InvalidOperationException($"{nameof(RoomSubScreen)}'s children should not be cleared as it will remove required components");
+
         [BackgroundDependencyLoader]
         private void load(AudioManager audio)
         {
@@ -55,6 +75,8 @@ namespace osu.Game.Screens.OnlinePlay.Match
 
             managerUpdated = beatmapManager.ItemUpdated.GetBoundCopy();
             managerUpdated.BindValueChanged(beatmapUpdated);
+
+            UserMods.BindValueChanged(_ => updateMods());
         }
 
         public override void OnEntering(IScreen last)
@@ -73,6 +95,7 @@ namespace osu.Game.Screens.OnlinePlay.Match
         {
             base.OnResuming(last);
             beginHandlingTrack();
+            updateMods();
         }
 
         public override bool OnExiting(IScreen next)
@@ -95,12 +118,17 @@ namespace osu.Game.Screens.OnlinePlay.Match
         {
             updateWorkingBeatmap();
 
-            var item = SelectedItem.Value;
+            if (SelectedItem.Value == null)
+                return;
 
-            Mods.Value = item?.RequiredMods?.ToArray() ?? Array.Empty<Mod>();
+            // Remove any user mods that are no longer allowed.
+            UserMods.Value = UserMods.Value
+                                     .Where(m => SelectedItem.Value.AllowedMods.Any(a => m.GetType() == a.GetType()))
+                                     .ToList();
 
-            if (item?.Ruleset != null)
+            updateMods();
-                Ruleset.Value = item.Ruleset.Value;
+
+            Ruleset.Value = SelectedItem.Value.Ruleset.Value;
         }
 
         private void beatmapUpdated(ValueChangedEvent<WeakReference<BeatmapSetInfo>> weakSet) => Schedule(updateWorkingBeatmap);
@@ -115,6 +143,14 @@ namespace osu.Game.Screens.OnlinePlay.Match
             Beatmap.Value = beatmapManager.GetWorkingBeatmap(localBeatmap);
         }
 
+        private void updateMods()
+        {
+            if (SelectedItem.Value == null)
+                return;
+
+            Mods.Value = UserMods.Value.Concat(SelectedItem.Value.RequiredMods).ToList();
+        }
+
         private void beginHandlingTrack()
         {
             Beatmap.BindValueChanged(applyLoopingToTrack, true);

osu.Game/Screens/OnlinePlay/Multiplayer/Match/MultiplayerMatchFooter.cs

@@ -3,13 +3,11 @@
 
 using System;
 using osu.Framework.Allocation;
-using osu.Framework.Bindables;
 using osu.Framework.Extensions.Color4Extensions;
 using osu.Framework.Graphics;
 using osu.Framework.Graphics.Containers;
 using osu.Framework.Graphics.Shapes;
 using osu.Game.Graphics;
-using osu.Game.Online.Rooms;
 using osuTK;
 
 namespace osu.Game.Screens.OnlinePlay.Multiplayer.Match
@@ -18,8 +16,6 @@ namespace osu.Game.Screens.OnlinePlay.Multiplayer.Match
     {
         public const float HEIGHT = 50;
 
-        public readonly Bindable<PlaylistItem> SelectedItem = new Bindable<PlaylistItem>();
-
         public Action OnReadyClick
         {
             set => readyButton.OnReadyClick = value;
@@ -41,7 +37,6 @@ namespace osu.Game.Screens.OnlinePlay.Multiplayer.Match
                     Anchor = Anchor.Centre,
                     Origin = Anchor.Centre,
                     Size = new Vector2(600, 50),
-                    SelectedItem = { BindTarget = SelectedItem }
                 }
             };
         }

osu.Game/Screens/OnlinePlay/Multiplayer/Match/MultiplayerReadyButton.cs

@@ -13,7 +13,6 @@ using osu.Game.Graphics;
 using osu.Game.Graphics.Backgrounds;
 using osu.Game.Online.API;
 using osu.Game.Online.Multiplayer;
-using osu.Game.Online.Rooms;
 using osu.Game.Screens.OnlinePlay.Components;
 using osuTK;
 
@@ -21,8 +20,6 @@ namespace osu.Game.Screens.OnlinePlay.Multiplayer.Match
 {
     public class MultiplayerReadyButton : MultiplayerRoomComposite
     {
-        public Bindable<PlaylistItem> SelectedItem => button.SelectedItem;
-
         public Action OnReadyClick
         {
             set => button.Action = value;

osu.Game/Screens/OnlinePlay/Multiplayer/MultiplayerMatchSongSelect.cs

@@ -1,70 +1,32 @@
 // Copyright (c) ppy Pty Ltd <contact@ppy.sh>. Licensed under the MIT Licence.
 // See the LICENCE file in the repository root for full licence text.
 
-using System.Collections.Generic;
-using System.Linq;
-using Humanizer;
 using osu.Framework.Allocation;
-using osu.Framework.Bindables;
-using osu.Framework.Graphics;
 using osu.Framework.Logging;
 using osu.Framework.Screens;
-using osu.Game.Beatmaps;
 using osu.Game.Graphics.UserInterface;
 using osu.Game.Online.Multiplayer;
 using osu.Game.Online.Rooms;
-using osu.Game.Overlays.Mods;
-using osu.Game.Rulesets;
 using osu.Game.Rulesets.Mods;
 using osu.Game.Screens.Select;
 
 namespace osu.Game.Screens.OnlinePlay.Multiplayer
 {
-    public class MultiplayerMatchSongSelect : SongSelect, IOnlinePlaySubScreen
+    public class MultiplayerMatchSongSelect : OnlinePlaySongSelect
     {
-        public string ShortTitle => "song selection";
-
-        public override string Title => ShortTitle.Humanize();
-
-        [Resolved(typeof(Room), nameof(Room.Playlist))]
-        private BindableList<PlaylistItem> playlist { get; set; }
-
         [Resolved]
         private StatefulMultiplayerClient client { get; set; }
 
         private LoadingLayer loadingLayer;
 
-        private WorkingBeatmap initialBeatmap;
-        private RulesetInfo initialRuleset;
-        private IReadOnlyList<Mod> initialMods;
-
-        private bool itemSelected;
-
-        public MultiplayerMatchSongSelect()
-        {
-            Padding = new MarginPadding { Horizontal = HORIZONTAL_OVERFLOW_PADDING };
-        }
-
         [BackgroundDependencyLoader]
         private void load()
         {
             AddInternal(loadingLayer = new LoadingLayer(true));
-            initialBeatmap = Beatmap.Value;
-            initialRuleset = Ruleset.Value;
-            initialMods = Mods.Value.ToList();
         }
 
-        protected override bool OnStart()
+        protected override void SelectItem(PlaylistItem item)
         {
-            itemSelected = true;
-            var item = new PlaylistItem();
-
-            item.Beatmap.Value = Beatmap.Value.BeatmapInfo;
-            item.Ruleset.Value = Ruleset.Value;
-
-            item.RequiredMods.Clear();
-            item.RequiredMods.AddRange(Mods.Value.Select(m => m.CreateCopy()));
-
             // If the client is already in a room, update via the client.
             // Otherwise, update the playlist directly in preparation for it to be submitted to the API on match creation.
             if (client.Room != null)
@@ -89,30 +51,14 @@ namespace osu.Game.Screens.OnlinePlay.Multiplayer
             }
             else
             {
-                playlist.Clear();
+                Playlist.Clear();
-                playlist.Add(item);
+                Playlist.Add(item);
                 this.Exit();
             }
-
-            return true;
-        }
-
-        public override bool OnExiting(IScreen next)
-        {
-            if (!itemSelected)
-            {
-                Beatmap.Value = initialBeatmap;
-                Ruleset.Value = initialRuleset;
-                Mods.Value = initialMods;
-            }
-
-            return base.OnExiting(next);
         }
 
         protected override BeatmapDetailArea CreateBeatmapDetailArea() => new PlayBeatmapDetailArea();
 
-        protected override ModSelectOverlay CreateModSelectOverlay() => new ModSelectOverlay(isValidMod);
+        protected override bool IsValidFreeMod(Mod mod) => base.IsValidFreeMod(mod) && !(mod is ModTimeRamp) && !(mod is ModRateAdjust) && !mod.RequiresConfiguration;
-
-        private bool isValidMod(Mod mod) => !(mod is ModAutoplay) && (mod as MultiMod)?.Mods.Any(mm => mm is ModAutoplay) != true;
     }
 }

osu.Game/Screens/OnlinePlay/Multiplayer/MultiplayerMatchSubScreen.cs

@@ -2,6 +2,7 @@
 // See the LICENCE file in the repository root for full licence text.
 
 using System;
+using System.Collections.Generic;
 using System.Collections.Specialized;
 using System.Diagnostics;
 using System.Linq;
@@ -13,12 +14,16 @@ using osu.Framework.Graphics.Containers;
 using osu.Framework.Screens;
 using osu.Game.Online.Multiplayer;
 using osu.Game.Online.Rooms;
+using osu.Game.Overlays.Mods;
+using osu.Game.Rulesets.Mods;
 using osu.Game.Screens.OnlinePlay.Components;
 using osu.Game.Screens.OnlinePlay.Match;
 using osu.Game.Screens.OnlinePlay.Match.Components;
 using osu.Game.Screens.OnlinePlay.Multiplayer.Match;
 using osu.Game.Screens.OnlinePlay.Multiplayer.Participants;
+using osu.Game.Screens.Play.HUD;
 using osu.Game.Users;
+using osuTK;
 using ParticipantsList = osu.Game.Screens.OnlinePlay.Multiplayer.Participants.ParticipantsList;
 
 namespace osu.Game.Screens.OnlinePlay.Multiplayer
@@ -36,7 +41,9 @@ namespace osu.Game.Screens.OnlinePlay.Multiplayer
         [Resolved]
         private OngoingOperationTracker ongoingOperationTracker { get; set; }
 
+        private ModSelectOverlay userModsSelectOverlay;
         private MultiplayerMatchSettingsOverlay settingsOverlay;
+        private Drawable userModsSection;
 
         private IBindable<bool> isConnected;
 
@@ -54,7 +61,7 @@ namespace osu.Game.Screens.OnlinePlay.Multiplayer
         [BackgroundDependencyLoader]
         private void load()
         {
-            InternalChildren = new Drawable[]
+            AddRangeInternal(new Drawable[]
             {
                 mainContent = new GridContainer
                 {
@@ -88,13 +95,6 @@ namespace osu.Game.Screens.OnlinePlay.Multiplayer
                                                 OpenSettings = () => settingsOverlay.Show()
                                             }
                                         },
-                                        new Drawable[]
-                                        {
-                                            new GridContainer
-                                            {
-                                                RelativeSizeAxes = Axes.Both,
-                                                Content = new[]
-                                                {
                                         new Drawable[]
                                         {
                                             new Container
@@ -102,6 +102,20 @@ namespace osu.Game.Screens.OnlinePlay.Multiplayer
                                                 RelativeSizeAxes = Axes.Both,
                                                 Padding = new MarginPadding { Horizontal = 5, Vertical = 10 },
                                                 Child = new GridContainer
+                                                {
+                                                    RelativeSizeAxes = Axes.Both,
+                                                    ColumnDimensions = new[]
+                                                    {
+                                                        new Dimension(GridSizeMode.Relative, size: 0.5f, maxSize: 400),
+                                                        new Dimension(),
+                                                        new Dimension(GridSizeMode.Relative, size: 0.5f, maxSize: 600),
+                                                    },
+                                                    Content = new[]
+                                                    {
+                                                        new Drawable[]
+                                                        {
+                                                            // Main left column
+                                                            new GridContainer
                                                             {
                                                                 RelativeSizeAxes = Axes.Both,
                                                                 RowDimensions = new[]
@@ -119,20 +133,63 @@ namespace osu.Game.Screens.OnlinePlay.Multiplayer
                                                                         },
                                                                     }
                                                                 }
-                                                            }
                                                             },
+                                                            // Spacer
+                                                            null,
+                                                            // Main right column
+                                                            new FillFlowContainer
+                                                            {
+                                                                RelativeSizeAxes = Axes.X,
+                                                                AutoSizeAxes = Axes.Y,
+                                                                Children = new[]
+                                                                {
                                                                     new FillFlowContainer
                                                                     {
-                                                            Anchor = Anchor.Centre,
-                                                            Origin = Anchor.Centre,
                                                                         RelativeSizeAxes = Axes.X,
                                                                         AutoSizeAxes = Axes.Y,
-                                                            Padding = new MarginPadding { Horizontal = 5 },
                                                                         Children = new Drawable[]
                                                                         {
                                                                             new OverlinedHeader("Beatmap"),
                                                                             new BeatmapSelectionControl { RelativeSizeAxes = Axes.X }
                                                                         }
+                                                                    },
+                                                                    userModsSection = new FillFlowContainer
+                                                                    {
+                                                                        RelativeSizeAxes = Axes.X,
+                                                                        AutoSizeAxes = Axes.Y,
+                                                                        Margin = new MarginPadding { Top = 10 },
+                                                                        Children = new Drawable[]
+                                                                        {
+                                                                            new OverlinedHeader("Extra mods"),
+                                                                            new FillFlowContainer
+                                                                            {
+                                                                                AutoSizeAxes = Axes.Both,
+                                                                                Direction = FillDirection.Horizontal,
+                                                                                Spacing = new Vector2(10, 0),
+                                                                                Children = new Drawable[]
+                                                                                {
+                                                                                    new PurpleTriangleButton
+                                                                                    {
+                                                                                        Anchor = Anchor.CentreLeft,
+                                                                                        Origin = Anchor.CentreLeft,
+                                                                                        Width = 90,
+                                                                                        Text = "Select",
+                                                                                        Action = () => userModsSelectOverlay.Show()
+                                                                                    },
+                                                                                    new ModDisplay
+                                                                                    {
+                                                                                        Anchor = Anchor.CentreLeft,
+                                                                                        Origin = Anchor.CentreLeft,
+                                                                                        DisplayUnrankedText = false,
+                                                                                        Current = UserMods,
+                                                                                        Scale = new Vector2(0.8f),
+                                                                                    },
+                                                                                }
+                                                                            }
+                                                                        }
+                                                                    }
+                                                                }
+                                                            }
                                                         }
                                                     }
                                                 }
@@ -162,7 +219,6 @@ namespace osu.Game.Screens.OnlinePlay.Multiplayer
                         {
                             new MultiplayerMatchFooter
                             {
-                                SelectedItem = { BindTarget = SelectedItem },
                                 OnReadyClick = onReadyClick
                             }
                         }
@@ -173,12 +229,24 @@ namespace osu.Game.Screens.OnlinePlay.Multiplayer
                         new Dimension(GridSizeMode.AutoSize),
                     }
                 },
+                new Container
+                {
+                    Anchor = Anchor.BottomLeft,
+                    Origin = Anchor.BottomLeft,
+                    RelativeSizeAxes = Axes.Both,
+                    Height = 0.5f,
+                    Child = userModsSelectOverlay = new UserModSelectOverlay
+                    {
+                        SelectedMods = { BindTarget = UserMods },
+                        IsValidMod = _ => false
+                    }
+                },
                 settingsOverlay = new MultiplayerMatchSettingsOverlay
                 {
                     RelativeSizeAxes = Axes.Both,
                     State = { Value = client.Room == null ? Visibility.Visible : Visibility.Hidden }
                 }
-            };
+            });
 
             if (client.Room == null)
             {
@@ -199,6 +267,7 @@ namespace osu.Game.Screens.OnlinePlay.Multiplayer
             base.LoadComplete();
 
             Playlist.BindCollectionChanged(onPlaylistChanged, true);
+            UserMods.BindValueChanged(onUserModsChanged);
 
             client.LoadRequested += onLoadRequested;
 
@@ -218,10 +287,39 @@ namespace osu.Game.Screens.OnlinePlay.Multiplayer
                 return true;
             }
 
+            if (userModsSelectOverlay.State.Value == Visibility.Visible)
+            {
+                userModsSelectOverlay.Hide();
+                return true;
+            }
+
             return base.OnBackButton();
         }
 
-        private void onPlaylistChanged(object sender, NotifyCollectionChangedEventArgs e) => SelectedItem.Value = Playlist.FirstOrDefault();
+        private void onPlaylistChanged(object sender, NotifyCollectionChangedEventArgs e)
+        {
+            SelectedItem.Value = Playlist.FirstOrDefault();
+
+            if (SelectedItem.Value?.AllowedMods.Any() != true)
+            {
+                userModsSection.Hide();
+                userModsSelectOverlay.Hide();
+                userModsSelectOverlay.IsValidMod = _ => false;
+            }
+            else
+            {
+                userModsSection.Show();
+                userModsSelectOverlay.IsValidMod = m => SelectedItem.Value.AllowedMods.Any(a => a.GetType() == m.GetType());
+            }
+        }
+
+        private void onUserModsChanged(ValueChangedEvent<IReadOnlyList<Mod>> mods)
+        {
+            if (client.Room == null)
+                return;
+
+            client.ChangeUserMods(mods.NewValue);
+        }
 
         private void onReadyClick()
         {
@@ -274,5 +372,13 @@ namespace osu.Game.Screens.OnlinePlay.Multiplayer
             if (client != null)
                 client.LoadRequested -= onLoadRequested;
         }
+
+        private class UserModSelectOverlay : ModSelectOverlay
+        {
+            public UserModSelectOverlay()
+            {
+                CustomiseButton.Alpha = 0;
+            }
+        }
     }
 }

osu.Game/Screens/OnlinePlay/Multiplayer/Participants/ParticipantPanel.cs

@@ -1,6 +1,7 @@
 // Copyright (c) ppy Pty Ltd <contact@ppy.sh>. Licensed under the MIT Licence.
 // See the LICENCE file in the repository root for full licence text.
 
+using System.Linq;
 using osu.Framework.Allocation;
 using osu.Framework.Extensions.Color4Extensions;
 using osu.Framework.Graphics;
@@ -15,6 +16,8 @@ using osu.Game.Graphics.Sprites;
 using osu.Game.Graphics.UserInterface;
 using osu.Game.Online.API;
 using osu.Game.Online.Multiplayer;
+using osu.Game.Rulesets;
+using osu.Game.Screens.Play.HUD;
 using osu.Game.Users;
 using osu.Game.Users.Drawables;
 using osuTK;
@@ -29,6 +32,10 @@ namespace osu.Game.Screens.OnlinePlay.Multiplayer.Participants
         [Resolved]
         private IAPIProvider api { get; set; }
 
+        [Resolved]
+        private RulesetStore rulesets { get; set; }
+
+        private ModDisplay userModsDisplay;
         private StateDisplay userStateDisplay;
         private SpriteIcon crown;
 
@@ -121,6 +128,19 @@ namespace osu.Game.Screens.OnlinePlay.Multiplayer.Participants
                                     }
                                 }
                             },
+                            new Container
+                            {
+                                Anchor = Anchor.CentreRight,
+                                Origin = Anchor.CentreRight,
+                                AutoSizeAxes = Axes.Both,
+                                Margin = new MarginPadding { Right = 70 },
+                                Child = userModsDisplay = new ModDisplay
+                                {
+                                    Scale = new Vector2(0.5f),
+                                    ExpansionMode = ExpansionMode.AlwaysContracted,
+                                    DisplayUnrankedText = false,
+                                }
+                            },
                             userStateDisplay = new StateDisplay
                             {
                                 Anchor = Anchor.CentreRight,
@@ -142,7 +162,10 @@ namespace osu.Game.Screens.OnlinePlay.Multiplayer.Participants
 
             const double fade_time = 50;
 
+            var ruleset = rulesets.GetRuleset(Room.Settings.RulesetID).CreateInstance();
+
             userStateDisplay.Status = User.State;
+            userModsDisplay.Current.Value = User.Mods.Select(m => m.ToMod(ruleset)).ToList();
 
             if (Room.Host?.Equals(User) == true)
                 crown.FadeIn(fade_time);

osu.Game/Screens/OnlinePlay/OngoingOperationTracker.cs

@@ -47,26 +47,21 @@ namespace osu.Game.Screens.OnlinePlay
 
         private void endOperationWithKnownLease(LeasedBindable<bool> lease)
         {
-            if (lease != leasedInProgress)
-                return;
-
             // for extra safety, marshal the end of operation back to the update thread if necessary.
             Scheduler.Add(() =>
             {
-                leasedInProgress?.Return();
+                if (lease != leasedInProgress)
+                    return;
+
+                // UnbindAll() is purposefully used instead of Return() - the two do roughly the same thing, with one difference:
+                // the former won't throw if the lease has already been returned before.
+                // this matters because framework can unbind the lease via the internal UnbindAllBindables(), which is not always detectable
+                // (it is in the case of disposal, but not in the case of screen exit - at least not cleanly).
+                leasedInProgress?.UnbindAll();
                 leasedInProgress = null;
             }, false);
         }
 
-        protected override void Dispose(bool isDisposing)
-        {
-            base.Dispose(isDisposing);
-
-            // base call does an UnbindAllBindables().
-            // clean up the leased reference here so that it doesn't get returned twice.
-            leasedInProgress = null;
-        }
-
         private class OngoingOperation : IDisposable
         {
             private readonly OngoingOperationTracker tracker;

osu.Game/Screens/OnlinePlay/OnlinePlaySongSelect.cs

@@ -0,0 +1,154 @@
+// Copyright (c) ppy Pty Ltd <contact@ppy.sh>. Licensed under the MIT Licence.
+// See the LICENCE file in the repository root for full licence text.
+
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using Humanizer;
+using osu.Framework.Allocation;
+using osu.Framework.Bindables;
+using osu.Framework.Graphics;
+using osu.Framework.Graphics.Containers;
+using osu.Framework.Screens;
+using osu.Game.Beatmaps;
+using osu.Game.Online.Rooms;
+using osu.Game.Overlays.Mods;
+using osu.Game.Rulesets;
+using osu.Game.Rulesets.Mods;
+using osu.Game.Screens.Select;
+using osu.Game.Utils;
+
+namespace osu.Game.Screens.OnlinePlay
+{
+    public abstract class OnlinePlaySongSelect : SongSelect, IOnlinePlaySubScreen
+    {
+        public string ShortTitle => "song selection";
+
+        public override string Title => ShortTitle.Humanize();
+
+        public override bool AllowEditing => false;
+
+        [Resolved(typeof(Room), nameof(Room.Playlist))]
+        protected BindableList<PlaylistItem> Playlist { get; private set; }
+
+        private readonly Bindable<IReadOnlyList<Mod>> freeMods = new Bindable<IReadOnlyList<Mod>>(Array.Empty<Mod>());
+        private readonly FreeModSelectOverlay freeModSelectOverlay;
+
+        private WorkingBeatmap initialBeatmap;
+        private RulesetInfo initialRuleset;
+        private IReadOnlyList<Mod> initialMods;
+        private bool itemSelected;
+
+        protected OnlinePlaySongSelect()
+        {
+            Padding = new MarginPadding { Horizontal = HORIZONTAL_OVERFLOW_PADDING };
+
+            freeModSelectOverlay = new FreeModSelectOverlay
+            {
+                SelectedMods = { BindTarget = freeMods },
+                IsValidMod = IsValidFreeMod,
+            };
+        }
+
+        [BackgroundDependencyLoader]
+        private void load()
+        {
+            initialBeatmap = Beatmap.Value;
+            initialRuleset = Ruleset.Value;
+            initialMods = Mods.Value.ToList();
+
+            FooterPanels.Add(freeModSelectOverlay);
+        }
+
+        protected override void LoadComplete()
+        {
+            base.LoadComplete();
+
+            // At this point, Mods contains both the required and allowed mods. For selection purposes, it should only contain the required mods.
+            // Similarly, freeMods is currently empty but should only contain the allowed mods.
+            Mods.Value = Playlist.FirstOrDefault()?.RequiredMods.Select(m => m.CreateCopy()).ToArray() ?? Array.Empty<Mod>();
+            freeMods.Value = Playlist.FirstOrDefault()?.AllowedMods.Select(m => m.CreateCopy()).ToArray() ?? Array.Empty<Mod>();
+
+            Ruleset.BindValueChanged(onRulesetChanged);
+        }
+
+        private void onRulesetChanged(ValueChangedEvent<RulesetInfo> ruleset)
+        {
+            freeMods.Value = Array.Empty<Mod>();
+        }
+
+        protected sealed override bool OnStart()
+        {
+            itemSelected = true;
+
+            var item = new PlaylistItem();
+
+            item.Beatmap.Value = Beatmap.Value.BeatmapInfo;
+            item.Ruleset.Value = Ruleset.Value;
+
+            item.RequiredMods.Clear();
+            item.RequiredMods.AddRange(Mods.Value.Select(m => m.CreateCopy()));
+
+            item.AllowedMods.Clear();
+            item.AllowedMods.AddRange(freeMods.Value.Select(m => m.CreateCopy()));
+
+            SelectItem(item);
+            return true;
+        }
+
+        /// <summary>
+        /// Invoked when the user has requested a selection of a beatmap.
+        /// </summary>
+        /// <param name="item">The resultant <see cref="PlaylistItem"/>. This item has not yet been added to the <see cref="Room"/>'s.</param>
+        protected abstract void SelectItem(PlaylistItem item);
+
+        public override bool OnBackButton()
+        {
+            if (freeModSelectOverlay.State.Value == Visibility.Visible)
+            {
+                freeModSelectOverlay.Hide();
+                return true;
+            }
+
+            return base.OnBackButton();
+        }
+
+        public override bool OnExiting(IScreen next)
+        {
+            if (!itemSelected)
+            {
+                Beatmap.Value = initialBeatmap;
+                Ruleset.Value = initialRuleset;
+                Mods.Value = initialMods;
+            }
+
+            return base.OnExiting(next);
+        }
+
+        protected override ModSelectOverlay CreateModSelectOverlay() => new SoloModSelectOverlay
+        {
+            IsValidMod = IsValidMod
+        };
+
+        protected override IEnumerable<(FooterButton, OverlayContainer)> CreateFooterButtons()
+        {
+            var buttons = base.CreateFooterButtons().ToList();
+            buttons.Insert(buttons.FindIndex(b => b.Item1 is FooterButtonMods) + 1, (new FooterButtonFreeMods { Current = freeMods }, freeModSelectOverlay));
+            return buttons;
+        }
+
+        /// <summary>
+        /// Checks whether a given <see cref="Mod"/> is valid for global selection.
+        /// </summary>
+        /// <param name="mod">The <see cref="Mod"/> to check.</param>
+        /// <returns>Whether <paramref name="mod"/> is a valid mod for online play.</returns>
+        protected virtual bool IsValidMod(Mod mod) => mod.HasImplementation && !ModUtils.FlattenMod(mod).Any(m => m is ModAutoplay);
+
+        /// <summary>
+        /// Checks whether a given <see cref="Mod"/> is valid for per-player free-mod selection.
+        /// </summary>
+        /// <param name="mod">The <see cref="Mod"/> to check.</param>
+        /// <returns>Whether <paramref name="mod"/> is a selectable free-mod.</returns>
+        protected virtual bool IsValidFreeMod(Mod mod) => IsValidMod(mod);
+    }
+}

osu.Game/Screens/OnlinePlay/Playlists/PlaylistsMatchSettingsOverlay.cs

@@ -183,7 +183,7 @@ namespace osu.Game.Screens.OnlinePlay.Playlists
                                                             Child = new GridContainer
                                                             {
                                                                 RelativeSizeAxes = Axes.X,
-                                                                Height = 300,
+                                                                Height = 500,
                                                                 Content = new[]
                                                                 {
                                                                     new Drawable[]

osu.Game/Screens/OnlinePlay/Playlists/PlaylistsReadyButton.cs

@@ -4,6 +4,7 @@
 using System;
 using osu.Framework.Allocation;
 using osu.Framework.Bindables;
+using osu.Game.Beatmaps;
 using osu.Game.Graphics;
 using osu.Game.Online.Rooms;
 using osu.Game.Screens.OnlinePlay.Components;
@@ -15,6 +16,9 @@ namespace osu.Game.Screens.OnlinePlay.Playlists
         [Resolved(typeof(Room), nameof(Room.EndDate))]
         private Bindable<DateTimeOffset?> endDate { get; set; }
 
+        [Resolved]
+        private IBindable<WorkingBeatmap> gameBeatmap { get; set; }
+
         public PlaylistsReadyButton()
         {
             Text = "Start";
@@ -32,7 +36,7 @@ namespace osu.Game.Screens.OnlinePlay.Playlists
         {
             base.Update();
 
-            Enabled.Value = endDate.Value != null && DateTimeOffset.UtcNow.AddSeconds(30).AddMilliseconds(GameBeatmap.Value.Track.Length) < endDate.Value;
+            Enabled.Value = endDate.Value != null && DateTimeOffset.UtcNow.AddSeconds(30).AddMilliseconds(gameBeatmap.Value.Track.Length) < endDate.Value;
         }
     }
 }

osu.Game/Screens/OnlinePlay/Playlists/PlaylistsRoomSubScreen.cs

@@ -13,7 +13,6 @@ using osu.Game.Online.Rooms;
 using osu.Game.Screens.OnlinePlay.Components;
 using osu.Game.Screens.OnlinePlay.Match;
 using osu.Game.Screens.OnlinePlay.Match.Components;
-using osu.Game.Screens.Select;
 using osu.Game.Users;
 using Footer = osu.Game.Screens.OnlinePlay.Match.Components.Footer;
 
@@ -44,7 +43,7 @@ namespace osu.Game.Screens.OnlinePlay.Playlists
         [BackgroundDependencyLoader]
         private void load()
         {
-            InternalChildren = new Drawable[]
+            AddRangeInternal(new Drawable[]
             {
                 mainContent = new GridContainer
                 {
@@ -175,7 +174,6 @@ namespace osu.Game.Screens.OnlinePlay.Playlists
                             new Footer
                             {
                                 OnStart = onStart,
-                                SelectedItem = { BindTarget = SelectedItem }
                             }
                         }
                     },
@@ -188,10 +186,10 @@ namespace osu.Game.Screens.OnlinePlay.Playlists
                 settingsOverlay = new PlaylistsMatchSettingsOverlay
                 {
                     RelativeSizeAxes = Axes.Both,
-                    EditPlaylist = () => this.Push(new MatchSongSelect()),
+                    EditPlaylist = () => this.Push(new PlaylistsSongSelect()),
                     State = { Value = roomId.Value == null ? Visibility.Visible : Visibility.Hidden }
                 }
-            };
+            });
 
             if (roomId.Value == null)
             {

osu.Game/Screens/OnlinePlay/Playlists/PlaylistsSongSelect.cs

@@ -1,48 +1,27 @@
 // Copyright (c) ppy Pty Ltd <contact@ppy.sh>. Licensed under the MIT Licence.
 // See the LICENCE file in the repository root for full licence text.
 
-using System;
 using System.Linq;
-using Humanizer;
 using osu.Framework.Allocation;
-using osu.Framework.Bindables;
-using osu.Framework.Graphics;
 using osu.Framework.Screens;
 using osu.Game.Beatmaps;
 using osu.Game.Online.Rooms;
-using osu.Game.Overlays.Mods;
-using osu.Game.Rulesets.Mods;
-using osu.Game.Screens.OnlinePlay;
 using osu.Game.Screens.OnlinePlay.Components;
+using osu.Game.Screens.Select;
 
-namespace osu.Game.Screens.Select
+namespace osu.Game.Screens.OnlinePlay.Playlists
 {
-    public class MatchSongSelect : SongSelect, IOnlinePlaySubScreen
+    public class PlaylistsSongSelect : OnlinePlaySongSelect
     {
-        public Action<PlaylistItem> Selected;
-
-        public string ShortTitle => "song selection";
-        public override string Title => ShortTitle.Humanize();
-
-        public override bool AllowEditing => false;
-
-        [Resolved(typeof(Room), nameof(Room.Playlist))]
-        protected BindableList<PlaylistItem> Playlist { get; private set; }
-
         [Resolved]
         private BeatmapManager beatmaps { get; set; }
 
-        public MatchSongSelect()
-        {
-            Padding = new MarginPadding { Horizontal = HORIZONTAL_OVERFLOW_PADDING };
-        }
-
         protected override BeatmapDetailArea CreateBeatmapDetailArea() => new MatchBeatmapDetailArea
         {
             CreateNewItem = createNewItem
         };
 
-        protected override bool OnStart()
+        protected override void SelectItem(PlaylistItem item)
         {
             switch (Playlist.Count)
             {
@@ -56,8 +35,6 @@ namespace osu.Game.Screens.Select
             }
 
             this.Exit();
-
-            return true;
         }
 
         private void createNewItem()
@@ -80,9 +57,5 @@ namespace osu.Game.Screens.Select
             item.RequiredMods.Clear();
             item.RequiredMods.AddRange(Mods.Value.Select(m => m.CreateCopy()));
         }
-
-        protected override ModSelectOverlay CreateModSelectOverlay() => new ModSelectOverlay(isValidMod);
-
-        private bool isValidMod(Mod mod) => !(mod is ModAutoplay) && (mod as MultiMod)?.Mods.Any(mm => mm is ModAutoplay) != true;
     }
 }

osu.Game/Screens/Select/Footer.cs

@@ -28,19 +28,16 @@ namespace osu.Game.Screens.Select
 
         private readonly List<OverlayContainer> overlays = new List<OverlayContainer>();
 
-        /// <param name="button">THe button to be added.</param>
+        /// <param name="button">The button to be added.</param>
         /// <param name="overlay">The <see cref="OverlayContainer"/> to be toggled by this button.</param>
         public void AddButton(FooterButton button, OverlayContainer overlay)
+        {
+            if (overlay != null)
             {
                 overlays.Add(overlay);
                 button.Action = () => showOverlay(overlay);
-
-            AddButton(button);
             }
 
-        /// <param name="button">Button to be added.</param>
-        public void AddButton(FooterButton button)
-        {
             button.Hovered = updateModeLight;
             button.HoverLost = updateModeLight;
 

osu.Game/Screens/Select/SongSelect.cs

@@ -263,9 +263,8 @@ namespace osu.Game.Screens.Select
 
             if (Footer != null)
             {
-                Footer.AddButton(new FooterButtonMods { Current = Mods }, ModSelect);
+                foreach (var (button, overlay) in CreateFooterButtons())
-                Footer.AddButton(new FooterButtonRandom { Action = triggerRandom });
+                    Footer.AddButton(button, overlay);
-                Footer.AddButton(new FooterButtonOptions(), BeatmapOptions);
 
                 BeatmapOptions.AddButton(@"Manage", @"collections", FontAwesome.Solid.Book, colours.Green, () => manageCollectionsDialog?.Show());
                 BeatmapOptions.AddButton(@"Delete", @"all difficulties", FontAwesome.Solid.Trash, colours.Pink, () => delete(Beatmap.Value.BeatmapSetInfo));
@@ -301,7 +300,18 @@ namespace osu.Game.Screens.Select
             }
         }
 
-        protected virtual ModSelectOverlay CreateModSelectOverlay() => new ModSelectOverlay();
+        /// <summary>
+        /// Creates the buttons to be displayed in the footer.
+        /// </summary>
+        /// <returns>A set of <see cref="FooterButton"/> and an optional <see cref="OverlayContainer"/> which the button opens when pressed.</returns>
+        protected virtual IEnumerable<(FooterButton, OverlayContainer)> CreateFooterButtons() => new (FooterButton, OverlayContainer)[]
+        {
+            (new FooterButtonMods { Current = Mods }, ModSelect),
+            (new FooterButtonRandom { Action = triggerRandom }, null),
+            (new FooterButtonOptions(), BeatmapOptions)
+        };
+
+        protected virtual ModSelectOverlay CreateModSelectOverlay() => new SoloModSelectOverlay();
 
         protected virtual void ApplyFilterToCarousel(FilterCriteria criteria)
         {

osu.Game/Tests/Visual/Multiplayer/TestMultiplayerClient.cs

@@ -3,6 +3,7 @@
 
 #nullable enable
 
+using System.Collections.Generic;
 using System.Diagnostics;
 using System.Linq;
 using System.Threading.Tasks;
@@ -11,6 +12,7 @@ using osu.Framework.Bindables;
 using osu.Game.Online.API;
 using osu.Game.Online.Multiplayer;
 using osu.Game.Online.Rooms;
+using osu.Game.Rulesets.Mods;
 using osu.Game.Users;
 
 namespace osu.Game.Tests.Visual.Multiplayer
@@ -122,6 +124,21 @@ namespace osu.Game.Tests.Visual.Multiplayer
             return Task.CompletedTask;
         }
 
+        public void ChangeUserMods(int userId, IEnumerable<Mod> newMods)
+            => ChangeUserMods(userId, newMods.Select(m => new APIMod(m)).ToList());
+
+        public void ChangeUserMods(int userId, IEnumerable<APIMod> newMods)
+        {
+            Debug.Assert(Room != null);
+            ((IMultiplayerClient)this).UserModsChanged(userId, newMods.ToList());
+        }
+
+        public override Task ChangeUserMods(IEnumerable<APIMod> newMods)
+        {
+            ChangeUserMods(api.LocalUser.Value.Id, newMods);
+            return Task.CompletedTask;
+        }
+
         public override Task StartMatch()
         {
             Debug.Assert(Room != null);

osu.Game/Utils/ModUtils.cs

@@ -0,0 +1,133 @@
+// Copyright (c) ppy Pty Ltd <contact@ppy.sh>. Licensed under the MIT Licence.
+// See the LICENCE file in the repository root for full licence text.
+
+using System;
+using System.Collections.Generic;
+using System.Diagnostics.CodeAnalysis;
+using System.Linq;
+using osu.Game.Rulesets.Mods;
+
+#nullable enable
+
+namespace osu.Game.Utils
+{
+    /// <summary>
+    /// A set of utilities to handle <see cref="Mod"/> combinations.
+    /// </summary>
+    public static class ModUtils
+    {
+        /// <summary>
+        /// Checks that all <see cref="Mod"/>s are compatible with each-other, and that all appear within a set of allowed types.
+        /// </summary>
+        /// <remarks>
+        /// The allowed types must contain exact <see cref="Mod"/> types for the respective <see cref="Mod"/>s to be allowed.
+        /// </remarks>
+        /// <param name="combination">The <see cref="Mod"/>s to check.</param>
+        /// <param name="allowedTypes">The set of allowed <see cref="Mod"/> types.</param>
+        /// <returns>Whether all <see cref="Mod"/>s are compatible with each-other and appear in the set of allowed types.</returns>
+        public static bool CheckCompatibleSetAndAllowed(IEnumerable<Mod> combination, IEnumerable<Type> allowedTypes)
+        {
+            // Prevent multiple-enumeration.
+            var combinationList = combination as ICollection<Mod> ?? combination.ToArray();
+            return CheckCompatibleSet(combinationList, out _) && CheckAllowed(combinationList, allowedTypes);
+        }
+
+        /// <summary>
+        /// Checks that all <see cref="Mod"/>s in a combination are compatible with each-other.
+        /// </summary>
+        /// <param name="combination">The <see cref="Mod"/> combination to check.</param>
+        /// <returns>Whether all <see cref="Mod"/>s in the combination are compatible with each-other.</returns>
+        public static bool CheckCompatibleSet(IEnumerable<Mod> combination)
+            => CheckCompatibleSet(combination, out _);
+
+        /// <summary>
+        /// Checks that all <see cref="Mod"/>s in a combination are compatible with each-other.
+        /// </summary>
+        /// <param name="combination">The <see cref="Mod"/> combination to check.</param>
+        /// <param name="invalidMods">Any invalid mods in the set.</param>
+        /// <returns>Whether all <see cref="Mod"/>s in the combination are compatible with each-other.</returns>
+        public static bool CheckCompatibleSet(IEnumerable<Mod> combination, [NotNullWhen(false)] out List<Mod>? invalidMods)
+        {
+            combination = FlattenMods(combination).ToArray();
+            invalidMods = null;
+
+            foreach (var mod in combination)
+            {
+                foreach (var type in mod.IncompatibleMods)
+                {
+                    foreach (var invalid in combination.Where(m => type.IsInstanceOfType(m)))
+                    {
+                        invalidMods ??= new List<Mod>();
+                        invalidMods.Add(invalid);
+                    }
+                }
+            }
+
+            return invalidMods == null;
+        }
+
+        /// <summary>
+        /// Checks that all <see cref="Mod"/>s in a combination appear within a set of allowed types.
+        /// </summary>
+        /// <remarks>
+        /// The set of allowed types must contain exact <see cref="Mod"/> types for the respective <see cref="Mod"/>s to be allowed.
+        /// </remarks>
+        /// <param name="combination">The <see cref="Mod"/> combination to check.</param>
+        /// <param name="allowedTypes">The set of allowed <see cref="Mod"/> types.</param>
+        /// <returns>Whether all <see cref="Mod"/>s in the combination are allowed.</returns>
+        public static bool CheckAllowed(IEnumerable<Mod> combination, IEnumerable<Type> allowedTypes)
+        {
+            var allowedSet = new HashSet<Type>(allowedTypes);
+
+            return combination.SelectMany(FlattenMod)
+                              .All(m => allowedSet.Contains(m.GetType()));
+        }
+
+        /// <summary>
+        /// Check the provided combination of mods are valid for a local gameplay session.
+        /// </summary>
+        /// <param name="mods">The mods to check.</param>
+        /// <param name="invalidMods">Invalid mods, if any were found. Can be null if all mods were valid.</param>
+        /// <returns>Whether the input mods were all valid. If false, <paramref name="invalidMods"/> will contain all invalid entries.</returns>
+        public static bool CheckValidForGameplay(IEnumerable<Mod> mods, out List<Mod>? invalidMods)
+        {
+            mods = mods.ToArray();
+
+            CheckCompatibleSet(mods, out invalidMods);
+
+            foreach (var mod in mods)
+            {
+                if (mod.Type == ModType.System || !mod.HasImplementation || mod is MultiMod)
+                {
+                    invalidMods ??= new List<Mod>();
+                    invalidMods.Add(mod);
+                }
+            }
+
+            return invalidMods == null;
+        }
+
+        /// <summary>
+        /// Flattens a set of <see cref="Mod"/>s, returning a new set with all <see cref="MultiMod"/>s removed.
+        /// </summary>
+        /// <param name="mods">The set of <see cref="Mod"/>s to flatten.</param>
+        /// <returns>The new set, containing all <see cref="Mod"/>s in <paramref name="mods"/> recursively with all <see cref="MultiMod"/>s removed.</returns>
+        public static IEnumerable<Mod> FlattenMods(IEnumerable<Mod> mods) => mods.SelectMany(FlattenMod);
+
+        /// <summary>
+        /// Flattens a <see cref="Mod"/>, returning a set of <see cref="Mod"/>s in-place of any <see cref="MultiMod"/>s.
+        /// </summary>
+        /// <param name="mod">The <see cref="Mod"/> to flatten.</param>
+        /// <returns>A set of singular "flattened" <see cref="Mod"/>s</returns>
+        public static IEnumerable<Mod> FlattenMod(Mod mod)
+        {
+            if (mod is MultiMod multi)
+            {
+                foreach (var m in multi.Mods.SelectMany(FlattenMod))
+                    yield return m;
+            }
+            else
+                yield return mod;
+        }
+    }
+}

osu.Game/osu.Game.csproj

@@ -20,11 +20,13 @@
   <ItemGroup Label="Package References">
     <PackageReference Include="DiffPlex" Version="1.6.3" />
     <PackageReference Include="Humanizer" Version="2.8.26" />
-    <PackageReference Include="Microsoft.AspNetCore.SignalR.Client" Version="3.1.10" />
+    <PackageReference Include="MessagePack" Version="2.2.85" />
-    <PackageReference Include="Microsoft.AspNetCore.SignalR.Protocols.MessagePack" Version="3.1.11" />
+    <PackageReference Include="Microsoft.AspNetCore.SignalR.Client" Version="5.0.2" />
-    <PackageReference Include="Microsoft.AspNetCore.SignalR.Protocols.NewtonsoftJson" Version="3.1.10" />
+    <PackageReference Include="Microsoft.AspNetCore.SignalR.Protocols.MessagePack" Version="5.0.2" />
+    <PackageReference Include="Microsoft.AspNetCore.SignalR.Protocols.NewtonsoftJson" Version="5.0.2" />
     <PackageReference Include="Microsoft.EntityFrameworkCore.Sqlite" Version="2.2.6" />
     <PackageReference Include="Microsoft.EntityFrameworkCore.Sqlite.Core" Version="2.2.6" />
+    <PackageReference Include="Microsoft.Extensions.Configuration.Abstractions" Version="2.2.0" />
     <PackageReference Include="Microsoft.NETCore.Targets" Version="3.1.0" />
     <PackageReference Include="Newtonsoft.Json" Version="12.0.3" />
     <PackageReference Include="ppy.osu.Framework" Version="2021.128.0" />

osu.iOS.props

@@ -80,6 +80,9 @@
   <ItemGroup>
     <PackageReference Include="Microsoft.AspNetCore.SignalR.Client" Version="3.0.3" />
     <PackageReference Include="Microsoft.Extensions.DependencyInjection" Version="3.0.3" />
+    <PackageReference Include="Microsoft.AspNetCore.SignalR.Protocols.MessagePack" Version="3.0.3" />
+    <PackageReference Include="MessagePack" Version="1.7.3.7" />
+    <PackageReference Include="MessagePack.Annotations" Version="2.2.85" />
   </ItemGroup>
   <!-- Xamarin.iOS does not automatically handle transitive dependencies from NuGet packages. -->
   <ItemGroup Label="Transitive Dependencies">