From 3741f05ab335d5baeb755bd4e370310698c1fe7f Mon Sep 17 00:00:00 2001
From: smoogipoo <smoogipoo@smgi.me>
Date: Tue, 2 Feb 2021 20:11:40 +0900
Subject: [PATCH 01/11] Refactor mod sections and make them overridable

---
 osu.Game/Overlays/Mods/ModSection.cs          | 39 +++++++++----------
 osu.Game/Overlays/Mods/ModSelectOverlay.cs    | 38 ++++++++++++++----
 .../Mods/Sections/AutomationSection.cs        | 19 ---------
 .../Mods/Sections/ConversionSection.cs        | 19 ---------
 .../Sections/DifficultyIncreaseSection.cs     | 19 ---------
 .../Sections/DifficultyReductionSection.cs    | 19 ---------
 osu.Game/Overlays/Mods/Sections/FunSection.cs | 19 ---------
 7 files changed, 50 insertions(+), 122 deletions(-)
 delete mode 100644 osu.Game/Overlays/Mods/Sections/AutomationSection.cs
 delete mode 100644 osu.Game/Overlays/Mods/Sections/ConversionSection.cs
 delete mode 100644 osu.Game/Overlays/Mods/Sections/DifficultyIncreaseSection.cs
 delete mode 100644 osu.Game/Overlays/Mods/Sections/DifficultyReductionSection.cs
 delete mode 100644 osu.Game/Overlays/Mods/Sections/FunSection.cs

diff --git a/osu.Game/Overlays/Mods/ModSection.cs b/osu.Game/Overlays/Mods/ModSection.cs
index 573d1e5355..89a3e2f5cd 100644
--- a/osu.Game/Overlays/Mods/ModSection.cs
+++ b/osu.Game/Overlays/Mods/ModSection.cs
@@ -11,26 +11,23 @@ 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
-        {
-            get => headerLabel.Text;
-            set => headerLabel.Text = value;
-        }
+        public Key[] ToggleKeys;
+
+        public readonly ModType ModType;
 
         public IEnumerable<Mod> SelectedMods => buttons.Select(b => b.SelectedMod).Where(m => m != null);
 
@@ -61,7 +58,7 @@ namespace osu.Game.Overlays.Mods
                 if (modContainers.Length == 0)
                 {
                     ModIconsLoaded = true;
-                    headerLabel.Hide();
+                    header.Hide();
                     Hide();
                     return;
                 }
@@ -76,7 +73,7 @@ namespace osu.Game.Overlays.Mods
 
                 buttons = modContainers.OfType<ModButton>().ToArray();
 
-                headerLabel.FadeIn(200);
+                header.FadeIn(200);
                 this.FadeIn(200);
             }
         }
@@ -153,23 +150,19 @@ 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
-                {
-                    Origin = Anchor.TopLeft,
-                    Anchor = Anchor.TopLeft,
-                    Position = new Vector2(0f, 0f),
-                    Font = OsuFont.GetFont(weight: FontWeight.Bold)
-                },
+                header = CreateHeader(type.Humanize(LetterCasing.Title)),
                 ButtonsContainer = new FillFlowContainer<ModButtonEmpty>
                 {
                     AutoSizeAxes = Axes.Y,
@@ -185,5 +178,11 @@ namespace osu.Game.Overlays.Mods
                 },
             };
         }
+
+        protected virtual Drawable CreateHeader(string text) => new OsuSpriteText
+        {
+            Font = OsuFont.GetFont(weight: FontWeight.Bold),
+            Text = text
+        };
     }
 }
diff --git a/osu.Game/Overlays/Mods/ModSelectOverlay.cs b/osu.Game/Overlays/Mods/ModSelectOverlay.cs
index 1258ba719d..fd6f771f16 100644
--- a/osu.Game/Overlays/Mods/ModSelectOverlay.cs
+++ b/osu.Game/Overlays/Mods/ModSelectOverlay.cs
@@ -19,7 +19,6 @@ 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 osuTK;
@@ -190,13 +189,31 @@ namespace osu.Game.Overlays.Mods
                                                 Width = content_width,
                                                 LayoutDuration = 200,
                                                 LayoutEasing = Easing.OutQuint,
-                                                Children = new ModSection[]
+                                                Children = new[]
                                                 {
-                                                    new DifficultyReductionSection { Action = modButtonPressed },
-                                                    new DifficultyIncreaseSection { Action = modButtonPressed },
-                                                    new AutomationSection { Action = modButtonPressed },
-                                                    new ConversionSection { Action = modButtonPressed },
-                                                    new FunSection { Action = modButtonPressed },
+                                                    CreateModSection(ModType.DifficultyReduction).With(s =>
+                                                    {
+                                                        s.ToggleKeys = new[] { Key.Q, Key.W, Key.E, Key.R, Key.T, Key.Y, Key.U, Key.I, Key.O, Key.P };
+                                                        s.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;
+                                                    }),
                                                 }
                                             },
                                         }
@@ -454,6 +471,13 @@ namespace osu.Game.Overlays.Mods
 
         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)
diff --git a/osu.Game/Overlays/Mods/Sections/AutomationSection.cs b/osu.Game/Overlays/Mods/Sections/AutomationSection.cs
deleted file mode 100644
index a2d7fec15f..0000000000
--- a/osu.Game/Overlays/Mods/Sections/AutomationSection.cs
+++ /dev/null
@@ -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";
-        }
-    }
-}
diff --git a/osu.Game/Overlays/Mods/Sections/ConversionSection.cs b/osu.Game/Overlays/Mods/Sections/ConversionSection.cs
deleted file mode 100644
index 24fd8c30dd..0000000000
--- a/osu.Game/Overlays/Mods/Sections/ConversionSection.cs
+++ /dev/null
@@ -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";
-        }
-    }
-}
diff --git a/osu.Game/Overlays/Mods/Sections/DifficultyIncreaseSection.cs b/osu.Game/Overlays/Mods/Sections/DifficultyIncreaseSection.cs
deleted file mode 100644
index 0b7ccd1f25..0000000000
--- a/osu.Game/Overlays/Mods/Sections/DifficultyIncreaseSection.cs
+++ /dev/null
@@ -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";
-        }
-    }
-}
diff --git a/osu.Game/Overlays/Mods/Sections/DifficultyReductionSection.cs b/osu.Game/Overlays/Mods/Sections/DifficultyReductionSection.cs
deleted file mode 100644
index 508e92508b..0000000000
--- a/osu.Game/Overlays/Mods/Sections/DifficultyReductionSection.cs
+++ /dev/null
@@ -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";
-        }
-    }
-}
diff --git a/osu.Game/Overlays/Mods/Sections/FunSection.cs b/osu.Game/Overlays/Mods/Sections/FunSection.cs
deleted file mode 100644
index af1f5836b1..0000000000
--- a/osu.Game/Overlays/Mods/Sections/FunSection.cs
+++ /dev/null
@@ -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";
-        }
-    }
-}

From 6d620264f48369f807a79983da19bf2ff37773e9 Mon Sep 17 00:00:00 2001
From: smoogipoo <smoogipoo@smgi.me>
Date: Tue, 2 Feb 2021 20:27:41 +0900
Subject: [PATCH 02/11] Allow mod buttons to not be stacked

---
 .../TestSceneModSelectOverlay.cs              | 62 ++++++++++++-------
 osu.Game/Overlays/Mods/ModSelectOverlay.cs    | 12 +++-
 2 files changed, 51 insertions(+), 23 deletions(-)

diff --git a/osu.Game.Tests/Visual/UserInterface/TestSceneModSelectOverlay.cs b/osu.Game.Tests/Visual/UserInterface/TestSceneModSelectOverlay.cs
index bd4010a7f3..71c549b433 100644
--- a/osu.Game.Tests/Visual/UserInterface/TestSceneModSelectOverlay.cs
+++ b/osu.Game.Tests/Visual/UserInterface/TestSceneModSelectOverlay.cs
@@ -38,28 +38,7 @@ namespace osu.Game.Tests.Visual.UserInterface
         }
 
         [SetUp]
-        public void SetUp() => Schedule(() =>
-        {
-            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 }
-                }
-            };
-        });
+        public void SetUp() => Schedule(() => createDisplay(() => new TestModSelectOverlay()));
 
         [SetUpSteps]
         public void SetUpSteps()
@@ -146,6 +125,18 @@ 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));
+        }
+
         private void testSingleMod(Mod mod)
         {
             selectNext(mod);
@@ -265,6 +256,28 @@ namespace osu.Game.Tests.Visual.UserInterface
 
         private void checkLabelColor(Func<Color4> getColour) => AddAssert("check label has expected colour", () => modSelect.MultiplierLabel.Colour.AverageColour == getColour());
 
+        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 : ModSelectOverlay
         {
             public new Bindable<IReadOnlyList<Mod>> SelectedMods => base.SelectedMods;
@@ -283,5 +296,10 @@ 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;
+        }
     }
 }
diff --git a/osu.Game/Overlays/Mods/ModSelectOverlay.cs b/osu.Game/Overlays/Mods/ModSelectOverlay.cs
index 1258ba719d..c7e856028a 100644
--- a/osu.Game/Overlays/Mods/ModSelectOverlay.cs
+++ b/osu.Game/Overlays/Mods/ModSelectOverlay.cs
@@ -22,6 +22,7 @@ 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;
@@ -43,6 +44,11 @@ namespace osu.Game.Overlays.Mods
 
         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;
+
         protected readonly FillFlowContainer<ModSection> ModSectionsContainer;
 
         protected readonly ModSettingsContainer ModSettingsContainer;
@@ -405,7 +411,11 @@ namespace osu.Game.Overlays.Mods
             if (mods.NewValue == null) return;
 
             foreach (var section in ModSectionsContainer.Children)
-                section.Mods = mods.NewValue[section.ModType].Where(isValidMod);
+            {
+                section.Mods = Stacked
+                    ? availableMods.Value[section.ModType]
+                    : ModUtils.FlattenMods(availableMods.Value[section.ModType]);
+            }
         }
 
         private void selectedModsChanged(ValueChangedEvent<IReadOnlyList<Mod>> mods)

From 75f81bfa062c9199759cd8257a10e64e543eb8ed Mon Sep 17 00:00:00 2001
From: smoogipoo <smoogipoo@smgi.me>
Date: Tue, 2 Feb 2021 20:35:31 +0900
Subject: [PATCH 03/11] Add back mod validation

---
 osu.Game/Overlays/Mods/ModSelectOverlay.cs | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/osu.Game/Overlays/Mods/ModSelectOverlay.cs b/osu.Game/Overlays/Mods/ModSelectOverlay.cs
index c7e856028a..775b0de1c0 100644
--- a/osu.Game/Overlays/Mods/ModSelectOverlay.cs
+++ b/osu.Game/Overlays/Mods/ModSelectOverlay.cs
@@ -412,9 +412,12 @@ namespace osu.Game.Overlays.Mods
 
             foreach (var section in ModSectionsContainer.Children)
             {
-                section.Mods = Stacked
-                    ? availableMods.Value[section.ModType]
-                    : ModUtils.FlattenMods(availableMods.Value[section.ModType]);
+                IEnumerable<Mod> modEnumeration = availableMods.Value[section.ModType];
+
+                if (!Stacked)
+                    modEnumeration = ModUtils.FlattenMods(modEnumeration);
+
+                section.Mods = modEnumeration.Where(isValidMod);
             }
         }
 

From 10ceddf3ffcf861f71aee5f4a681441b15913226 Mon Sep 17 00:00:00 2001
From: smoogipoo <smoogipoo@smgi.me>
Date: Tue, 2 Feb 2021 20:47:50 +0900
Subject: [PATCH 04/11] Make IsValidMod adjustable

---
 .../TestSceneModSelectOverlay.cs              | 16 ++++++
 osu.Game/Overlays/Mods/ModSelectOverlay.cs    | 54 ++++++++++++++++---
 .../Multiplayer/MultiplayerMatchSongSelect.cs |  2 +-
 osu.Game/Screens/Select/MatchSongSelect.cs    |  2 +-
 4 files changed, 64 insertions(+), 10 deletions(-)

diff --git a/osu.Game.Tests/Visual/UserInterface/TestSceneModSelectOverlay.cs b/osu.Game.Tests/Visual/UserInterface/TestSceneModSelectOverlay.cs
index 71c549b433..9cf8b95ddf 100644
--- a/osu.Game.Tests/Visual/UserInterface/TestSceneModSelectOverlay.cs
+++ b/osu.Game.Tests/Visual/UserInterface/TestSceneModSelectOverlay.cs
@@ -137,6 +137,22 @@ namespace osu.Game.Tests.Visual.UserInterface
             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));
+            AddAssert("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);
+            AddAssert("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)));
+        }
+
         private void testSingleMod(Mod mod)
         {
             selectNext(mod);
diff --git a/osu.Game/Overlays/Mods/ModSelectOverlay.cs b/osu.Game/Overlays/Mods/ModSelectOverlay.cs
index 775b0de1c0..61e4b45495 100644
--- a/osu.Game/Overlays/Mods/ModSelectOverlay.cs
+++ b/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;
@@ -31,7 +32,6 @@ namespace osu.Game.Overlays.Mods
 {
     public class ModSelectOverlay : WaveOverlayContainer
     {
-        private readonly Func<Mod, bool> isValidMod;
         public const float HEIGHT = 510;
 
         protected readonly TriangleButton DeselectAllButton;
@@ -49,6 +49,23 @@ namespace osu.Game.Overlays.Mods
         /// </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;
@@ -67,10 +84,8 @@ namespace osu.Game.Overlays.Mods
 
         private SampleChannel sampleOn, sampleOff;
 
-        public ModSelectOverlay(Func<Mod, bool> isValidMod = null)
+        public ModSelectOverlay()
         {
-            this.isValidMod = isValidMod ?? (m => true);
-
             Waves.FirstWaveColour = Color4Extensions.FromHex(@"19b0e2");
             Waves.SecondWaveColour = Color4Extensions.FromHex(@"2280a2");
             Waves.ThirdWaveColour = Color4Extensions.FromHex(@"005774");
@@ -351,7 +366,7 @@ namespace osu.Game.Overlays.Mods
         {
             base.LoadComplete();
 
-            availableMods.BindValueChanged(availableModsChanged, true);
+            availableMods.BindValueChanged(_ => updateAvailableMods(), true);
             SelectedMods.BindValueChanged(selectedModsChanged, true);
         }
 
@@ -406,9 +421,10 @@ 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)
             {
@@ -417,10 +433,32 @@ namespace osu.Game.Overlays.Mods
                 if (!Stacked)
                     modEnumeration = ModUtils.FlattenMods(modEnumeration);
 
-                section.Mods = modEnumeration.Where(isValidMod);
+                section.Mods = modEnumeration.Select(getValidModOrNull).Where(m => m != null);
             }
         }
 
+        /// <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 selectedModsChanged(ValueChangedEvent<IReadOnlyList<Mod>> mods)
         {
             foreach (var section in ModSectionsContainer.Children)
diff --git a/osu.Game/Screens/OnlinePlay/Multiplayer/MultiplayerMatchSongSelect.cs b/osu.Game/Screens/OnlinePlay/Multiplayer/MultiplayerMatchSongSelect.cs
index ebc06d2445..5bf9b1ee7e 100644
--- a/osu.Game/Screens/OnlinePlay/Multiplayer/MultiplayerMatchSongSelect.cs
+++ b/osu.Game/Screens/OnlinePlay/Multiplayer/MultiplayerMatchSongSelect.cs
@@ -111,7 +111,7 @@ namespace osu.Game.Screens.OnlinePlay.Multiplayer
 
         protected override BeatmapDetailArea CreateBeatmapDetailArea() => new PlayBeatmapDetailArea();
 
-        protected override ModSelectOverlay CreateModSelectOverlay() => new ModSelectOverlay(isValidMod);
+        protected override ModSelectOverlay CreateModSelectOverlay() => new ModSelectOverlay { IsValidMod = isValidMod };
 
         private bool isValidMod(Mod mod) => !(mod is ModAutoplay) && (mod as MultiMod)?.Mods.Any(mm => mm is ModAutoplay) != true;
     }
diff --git a/osu.Game/Screens/Select/MatchSongSelect.cs b/osu.Game/Screens/Select/MatchSongSelect.cs
index ed47b5d5ac..1bb7374ce3 100644
--- a/osu.Game/Screens/Select/MatchSongSelect.cs
+++ b/osu.Game/Screens/Select/MatchSongSelect.cs
@@ -81,7 +81,7 @@ namespace osu.Game.Screens.Select
             item.RequiredMods.AddRange(Mods.Value.Select(m => m.CreateCopy()));
         }
 
-        protected override ModSelectOverlay CreateModSelectOverlay() => new ModSelectOverlay(isValidMod);
+        protected override ModSelectOverlay CreateModSelectOverlay() => new ModSelectOverlay { IsValidMod = isValidMod };
 
         private bool isValidMod(Mod mod) => !(mod is ModAutoplay) && (mod as MultiMod)?.Mods.Any(mm => mm is ModAutoplay) != true;
     }

From 50e92bd0ed729a2d4aa551bea13a66f37de6035c Mon Sep 17 00:00:00 2001
From: smoogipoo <smoogipoo@smgi.me>
Date: Tue, 2 Feb 2021 20:50:54 +0900
Subject: [PATCH 05/11] Fix selection not being preserved when IsValidMod
 changes

---
 .../UserInterface/TestSceneModSelectOverlay.cs       | 12 ++++++++++++
 osu.Game/Overlays/Mods/ModSection.cs                 |  6 +++---
 osu.Game/Overlays/Mods/ModSelectOverlay.cs           | 11 ++++++++---
 3 files changed, 23 insertions(+), 6 deletions(-)

diff --git a/osu.Game.Tests/Visual/UserInterface/TestSceneModSelectOverlay.cs b/osu.Game.Tests/Visual/UserInterface/TestSceneModSelectOverlay.cs
index 9cf8b95ddf..81edcd8db8 100644
--- a/osu.Game.Tests/Visual/UserInterface/TestSceneModSelectOverlay.cs
+++ b/osu.Game.Tests/Visual/UserInterface/TestSceneModSelectOverlay.cs
@@ -153,6 +153,18 @@ namespace osu.Game.Tests.Visual.UserInterface
             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);
diff --git a/osu.Game/Overlays/Mods/ModSection.cs b/osu.Game/Overlays/Mods/ModSection.cs
index 573d1e5355..4c629aef54 100644
--- a/osu.Game/Overlays/Mods/ModSection.cs
+++ b/osu.Game/Overlays/Mods/ModSection.cs
@@ -130,13 +130,13 @@ 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)
             {
diff --git a/osu.Game/Overlays/Mods/ModSelectOverlay.cs b/osu.Game/Overlays/Mods/ModSelectOverlay.cs
index 61e4b45495..fcec6f3926 100644
--- a/osu.Game/Overlays/Mods/ModSelectOverlay.cs
+++ b/osu.Game/Overlays/Mods/ModSelectOverlay.cs
@@ -367,7 +367,7 @@ namespace osu.Game.Overlays.Mods
             base.LoadComplete();
 
             availableMods.BindValueChanged(_ => updateAvailableMods(), true);
-            SelectedMods.BindValueChanged(selectedModsChanged, true);
+            SelectedMods.BindValueChanged(_ => updateSelectedButtons(), true);
         }
 
         protected override void PopOut()
@@ -435,6 +435,8 @@ namespace osu.Game.Overlays.Mods
 
                 section.Mods = modEnumeration.Select(getValidModOrNull).Where(m => m != null);
             }
+
+            updateSelectedButtons();
         }
 
         /// <summary>
@@ -459,10 +461,13 @@ namespace osu.Game.Overlays.Mods
             return validSubset.Length == 1 ? validSubset[0] : new MultiMod(validSubset);
         }
 
-        private void selectedModsChanged(ValueChangedEvent<IReadOnlyList<Mod>> mods)
+        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();
         }

From e58ece9e108b757a72aaff635090ad00b245aa5a Mon Sep 17 00:00:00 2001
From: smoogipoo <smoogipoo@smgi.me>
Date: Tue, 2 Feb 2021 20:58:31 +0900
Subject: [PATCH 06/11] Make ModSelectOverlay abstract

---
 .../Visual/UserInterface/TestSceneModSelectOverlay.cs    | 2 +-
 .../Visual/UserInterface/TestSceneModSettings.cs         | 2 +-
 osu.Game/Overlays/Mods/ModSelectOverlay.cs               | 4 ++--
 osu.Game/Overlays/Mods/SoloModSelectOverlay.cs           | 9 +++++++++
 .../OnlinePlay/Multiplayer/MultiplayerMatchSongSelect.cs | 2 +-
 osu.Game/Screens/Select/MatchSongSelect.cs               | 2 +-
 osu.Game/Screens/Select/SongSelect.cs                    | 2 +-
 7 files changed, 16 insertions(+), 7 deletions(-)
 create mode 100644 osu.Game/Overlays/Mods/SoloModSelectOverlay.cs

diff --git a/osu.Game.Tests/Visual/UserInterface/TestSceneModSelectOverlay.cs b/osu.Game.Tests/Visual/UserInterface/TestSceneModSelectOverlay.cs
index 81edcd8db8..92104cfc72 100644
--- a/osu.Game.Tests/Visual/UserInterface/TestSceneModSelectOverlay.cs
+++ b/osu.Game.Tests/Visual/UserInterface/TestSceneModSelectOverlay.cs
@@ -306,7 +306,7 @@ namespace osu.Game.Tests.Visual.UserInterface
             };
         }
 
-        private class TestModSelectOverlay : ModSelectOverlay
+        private class TestModSelectOverlay : SoloModSelectOverlay
         {
             public new Bindable<IReadOnlyList<Mod>> SelectedMods => base.SelectedMods;
 
diff --git a/osu.Game.Tests/Visual/UserInterface/TestSceneModSettings.cs b/osu.Game.Tests/Visual/UserInterface/TestSceneModSettings.cs
index 8614700b15..3c889bdec4 100644
--- a/osu.Game.Tests/Visual/UserInterface/TestSceneModSettings.cs
+++ b/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;
diff --git a/osu.Game/Overlays/Mods/ModSelectOverlay.cs b/osu.Game/Overlays/Mods/ModSelectOverlay.cs
index fcec6f3926..75ad90f065 100644
--- a/osu.Game/Overlays/Mods/ModSelectOverlay.cs
+++ b/osu.Game/Overlays/Mods/ModSelectOverlay.cs
@@ -30,7 +30,7 @@ using osuTK.Input;
 
 namespace osu.Game.Overlays.Mods
 {
-    public class ModSelectOverlay : WaveOverlayContainer
+    public abstract class ModSelectOverlay : WaveOverlayContainer
     {
         public const float HEIGHT = 510;
 
@@ -84,7 +84,7 @@ namespace osu.Game.Overlays.Mods
 
         private SampleChannel sampleOn, sampleOff;
 
-        public ModSelectOverlay()
+        protected ModSelectOverlay()
         {
             Waves.FirstWaveColour = Color4Extensions.FromHex(@"19b0e2");
             Waves.SecondWaveColour = Color4Extensions.FromHex(@"2280a2");
diff --git a/osu.Game/Overlays/Mods/SoloModSelectOverlay.cs b/osu.Game/Overlays/Mods/SoloModSelectOverlay.cs
new file mode 100644
index 0000000000..8f6819d7ff
--- /dev/null
+++ b/osu.Game/Overlays/Mods/SoloModSelectOverlay.cs
@@ -0,0 +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.
+
+namespace osu.Game.Overlays.Mods
+{
+    public class SoloModSelectOverlay : ModSelectOverlay
+    {
+    }
+}
diff --git a/osu.Game/Screens/OnlinePlay/Multiplayer/MultiplayerMatchSongSelect.cs b/osu.Game/Screens/OnlinePlay/Multiplayer/MultiplayerMatchSongSelect.cs
index 5bf9b1ee7e..930f70d087 100644
--- a/osu.Game/Screens/OnlinePlay/Multiplayer/MultiplayerMatchSongSelect.cs
+++ b/osu.Game/Screens/OnlinePlay/Multiplayer/MultiplayerMatchSongSelect.cs
@@ -111,7 +111,7 @@ namespace osu.Game.Screens.OnlinePlay.Multiplayer
 
         protected override BeatmapDetailArea CreateBeatmapDetailArea() => new PlayBeatmapDetailArea();
 
-        protected override ModSelectOverlay CreateModSelectOverlay() => new ModSelectOverlay { IsValidMod = isValidMod };
+        protected override ModSelectOverlay CreateModSelectOverlay() => new SoloModSelectOverlay { IsValidMod = isValidMod };
 
         private bool isValidMod(Mod mod) => !(mod is ModAutoplay) && (mod as MultiMod)?.Mods.Any(mm => mm is ModAutoplay) != true;
     }
diff --git a/osu.Game/Screens/Select/MatchSongSelect.cs b/osu.Game/Screens/Select/MatchSongSelect.cs
index 1bb7374ce3..e181370cf7 100644
--- a/osu.Game/Screens/Select/MatchSongSelect.cs
+++ b/osu.Game/Screens/Select/MatchSongSelect.cs
@@ -81,7 +81,7 @@ namespace osu.Game.Screens.Select
             item.RequiredMods.AddRange(Mods.Value.Select(m => m.CreateCopy()));
         }
 
-        protected override ModSelectOverlay CreateModSelectOverlay() => new ModSelectOverlay { IsValidMod = isValidMod };
+        protected override ModSelectOverlay CreateModSelectOverlay() => new SoloModSelectOverlay { IsValidMod = isValidMod };
 
         private bool isValidMod(Mod mod) => !(mod is ModAutoplay) && (mod as MultiMod)?.Mods.Any(mm => mm is ModAutoplay) != true;
     }
diff --git a/osu.Game/Screens/Select/SongSelect.cs b/osu.Game/Screens/Select/SongSelect.cs
index 4fca77a176..ff49dd9f7e 100644
--- a/osu.Game/Screens/Select/SongSelect.cs
+++ b/osu.Game/Screens/Select/SongSelect.cs
@@ -301,7 +301,7 @@ namespace osu.Game.Screens.Select
             }
         }
 
-        protected virtual ModSelectOverlay CreateModSelectOverlay() => new ModSelectOverlay();
+        protected virtual ModSelectOverlay CreateModSelectOverlay() => new SoloModSelectOverlay();
 
         protected virtual void ApplyFilterToCarousel(FilterCriteria criteria)
         {

From 728f8599b2bedbc721481c2bafb017a130177d25 Mon Sep 17 00:00:00 2001
From: smoogipoo <smoogipoo@smgi.me>
Date: Tue, 2 Feb 2021 21:06:32 +0900
Subject: [PATCH 07/11] Move incompatible mod deselection to SoloModOverlay

---
 osu.Game/Overlays/Mods/ModSelectOverlay.cs    | 23 ++++++++-----------
 .../Overlays/Mods/SoloModSelectOverlay.cs     |  9 ++++++++
 2 files changed, 18 insertions(+), 14 deletions(-)

diff --git a/osu.Game/Overlays/Mods/ModSelectOverlay.cs b/osu.Game/Overlays/Mods/ModSelectOverlay.cs
index 75ad90f065..c400e4cc43 100644
--- a/osu.Game/Overlays/Mods/ModSelectOverlay.cs
+++ b/osu.Game/Overlays/Mods/ModSelectOverlay.cs
@@ -349,19 +349,6 @@ 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();
@@ -496,7 +483,7 @@ namespace osu.Game.Overlays.Mods
             {
                 if (State.Value == Visibility.Visible) sampleOn?.Play();
 
-                deselectTypes(selectedMod.IncompatibleMods, true);
+                OnModSelected(selectedMod);
 
                 if (selectedMod.RequiresConfiguration) ModSettingsContainer.Show();
             }
@@ -508,6 +495,14 @@ namespace osu.Game.Overlays.Mods
             refreshSelectedMods();
         }
 
+        /// <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();
 
         #region Disposal
diff --git a/osu.Game/Overlays/Mods/SoloModSelectOverlay.cs b/osu.Game/Overlays/Mods/SoloModSelectOverlay.cs
index 8f6819d7ff..d039ad1f98 100644
--- a/osu.Game/Overlays/Mods/SoloModSelectOverlay.cs
+++ b/osu.Game/Overlays/Mods/SoloModSelectOverlay.cs
@@ -1,9 +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);
+        }
     }
 }

From 643c0605d85cf7808394c4b2fe3ea4f39b62906b Mon Sep 17 00:00:00 2001
From: smoogipoo <smoogipoo@smgi.me>
Date: Tue, 2 Feb 2021 21:14:38 +0900
Subject: [PATCH 08/11] Implement the freemod selection overlay

---
 .../TestSceneFreeModSelectOverlay.cs          |  21 +++
 osu.Game/Overlays/Mods/ModSection.cs          |  15 ++-
 osu.Game/Overlays/Mods/ModSelectOverlay.cs    |  19 +--
 .../OnlinePlay/FreeModSelectOverlay.cs        | 120 ++++++++++++++++++
 4 files changed, 165 insertions(+), 10 deletions(-)
 create mode 100644 osu.Game.Tests/Visual/Multiplayer/TestSceneFreeModSelectOverlay.cs
 create mode 100644 osu.Game/Screens/OnlinePlay/FreeModSelectOverlay.cs

diff --git a/osu.Game.Tests/Visual/Multiplayer/TestSceneFreeModSelectOverlay.cs b/osu.Game.Tests/Visual/Multiplayer/TestSceneFreeModSelectOverlay.cs
new file mode 100644
index 0000000000..26a0301d8a
--- /dev/null
+++ b/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 }
+            };
+        });
+    }
+}
diff --git a/osu.Game/Overlays/Mods/ModSection.cs b/osu.Game/Overlays/Mods/ModSection.cs
index b3ddd30772..87a45ebf63 100644
--- a/osu.Game/Overlays/Mods/ModSection.cs
+++ b/osu.Game/Overlays/Mods/ModSection.cs
@@ -94,7 +94,20 @@ namespace osu.Game.Overlays.Mods
             return base.OnKeyDown(e);
         }
 
-        public void DeselectAll() => DeselectTypes(buttons.Select(b => b.SelectedMod?.GetType()).Where(t => t != null));
+        /// <summary>
+        /// Selects all mods.
+        /// </summary>
+        public void SelectAll()
+        {
+            foreach (var button in buttons.Where(b => !b.Selected))
+                button.SelectAt(0);
+        }
+
+        /// <summary>
+        /// Deselects all mods.
+        /// </summary>
+        /// <param name="immediate">Set to true to bypass animations and update selections immediately.</param>
+        public void DeselectAll(bool immediate = false) => DeselectTypes(buttons.Select(b => b.SelectedMod?.GetType()).Where(t => t != null), immediate);
 
         /// <summary>
         /// Deselect one or more mods in this section.
diff --git a/osu.Game/Overlays/Mods/ModSelectOverlay.cs b/osu.Game/Overlays/Mods/ModSelectOverlay.cs
index e064a6fb84..8225c1b6bb 100644
--- a/osu.Game/Overlays/Mods/ModSelectOverlay.cs
+++ b/osu.Game/Overlays/Mods/ModSelectOverlay.cs
@@ -37,8 +37,11 @@ namespace osu.Game.Overlays.Mods
         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;
@@ -79,8 +82,6 @@ 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;
 
         protected ModSelectOverlay()
@@ -269,7 +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,
@@ -283,7 +284,7 @@ namespace osu.Game.Overlays.Mods
                                             Vertical = 15,
                                             Horizontal = OsuScreen.HORIZONTAL_OVERFLOW_PADDING
                                         },
-                                        Children = new Drawable[]
+                                        Children = new[]
                                         {
                                             DeselectAllButton = new TriangleButton
                                             {
@@ -310,7 +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),
@@ -378,8 +379,8 @@ namespace osu.Game.Overlays.Mods
         {
             base.PopOut();
 
-            footerContainer.MoveToX(content_width, WaveContainer.DISAPPEAR_DURATION, Easing.InSine);
-            footerContainer.FadeOut(WaveContainer.DISAPPEAR_DURATION, Easing.InSine);
+            FooterContainer.MoveToX(content_width, WaveContainer.DISAPPEAR_DURATION, Easing.InSine);
+            FooterContainer.FadeOut(WaveContainer.DISAPPEAR_DURATION, Easing.InSine);
 
             foreach (var section in ModSectionsContainer.Children)
             {
@@ -393,8 +394,8 @@ namespace osu.Game.Overlays.Mods
         {
             base.PopIn();
 
-            footerContainer.MoveToX(0, WaveContainer.APPEAR_DURATION, Easing.OutQuint);
-            footerContainer.FadeIn(WaveContainer.APPEAR_DURATION, Easing.OutQuint);
+            FooterContainer.MoveToX(0, WaveContainer.APPEAR_DURATION, Easing.OutQuint);
+            FooterContainer.FadeIn(WaveContainer.APPEAR_DURATION, Easing.OutQuint);
 
             foreach (var section in ModSectionsContainer.Children)
             {
diff --git a/osu.Game/Screens/OnlinePlay/FreeModSelectOverlay.cs b/osu.Game/Screens/OnlinePlay/FreeModSelectOverlay.cs
new file mode 100644
index 0000000000..628199309a
--- /dev/null
+++ b/osu.Game/Screens/OnlinePlay/FreeModSelectOverlay.cs
@@ -0,0 +1,120 @@
+// 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.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 FreeModSelectOverlay()
+        {
+            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(true);
+        }
+
+        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,
+                Width = 175,
+                Child = checkbox = new HeaderCheckbox
+                {
+                    LabelText = text,
+                    Changed = onCheckboxChanged
+                }
+            };
+
+            private void onCheckboxChanged(bool value)
+            {
+                foreach (var button in ButtonsContainer.OfType<ModButton>())
+                {
+                    if (value)
+                        button.SelectAt(0);
+                    else
+                        button.Deselect();
+                }
+            }
+
+            protected override void Update()
+            {
+                base.Update();
+
+                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 void OnUserChange(bool value)
+            {
+                base.OnUserChange(value);
+                Changed?.Invoke(value);
+            }
+        }
+    }
+}

From f25535548ae1910215fff01186cac34285cdac81 Mon Sep 17 00:00:00 2001
From: smoogipoo <smoogipoo@smgi.me>
Date: Tue, 2 Feb 2021 21:20:16 +0900
Subject: [PATCH 09/11] Fix buzzing on select all/deselect all

---
 osu.Game/Overlays/Mods/ModSelectOverlay.cs | 14 ++++++++++++--
 1 file changed, 12 insertions(+), 2 deletions(-)

diff --git a/osu.Game/Overlays/Mods/ModSelectOverlay.cs b/osu.Game/Overlays/Mods/ModSelectOverlay.cs
index 8225c1b6bb..c308dc2451 100644
--- a/osu.Game/Overlays/Mods/ModSelectOverlay.cs
+++ b/osu.Game/Overlays/Mods/ModSelectOverlay.cs
@@ -14,6 +14,7 @@ using osu.Framework.Graphics;
 using osu.Framework.Graphics.Containers;
 using osu.Framework.Graphics.Shapes;
 using osu.Framework.Input.Events;
+using osu.Framework.Threading;
 using osu.Game.Graphics;
 using osu.Game.Graphics.Backgrounds;
 using osu.Game.Graphics.Containers;
@@ -495,11 +496,17 @@ namespace osu.Game.Overlays.Mods
                 MultiplierLabel.FadeColour(Color4.White, 200);
         }
 
+        private ScheduledDelegate sampleOnDelegate;
+        private ScheduledDelegate sampleOffDelegate;
+
         private void modButtonPressed(Mod selectedMod)
         {
             if (selectedMod != null)
             {
-                if (State.Value == Visibility.Visible) sampleOn?.Play();
+                // Fixes buzzing when multiple mods are selected in the same frame.
+                sampleOnDelegate?.Cancel();
+                if (State.Value == Visibility.Visible)
+                    sampleOnDelegate = Scheduler.Add(() => sampleOn?.Play());
 
                 OnModSelected(selectedMod);
 
@@ -507,7 +514,10 @@ namespace osu.Game.Overlays.Mods
             }
             else
             {
-                if (State.Value == Visibility.Visible) sampleOff?.Play();
+                // Fixes buzzing when multiple mods are deselected in the same frame.
+                sampleOffDelegate?.Cancel();
+                if (State.Value == Visibility.Visible)
+                    sampleOffDelegate = Scheduler.Add(() => sampleOff?.Play());
             }
 
             refreshSelectedMods();

From 5a56e2ba4b66ae8058157a3b32935f154d0f0c02 Mon Sep 17 00:00:00 2001
From: smoogipoo <smoogipoo@smgi.me>
Date: Tue, 2 Feb 2021 21:29:00 +0900
Subject: [PATCH 10/11] Fix sound duplication due to checkbox

---
 osu.Game/Graphics/UserInterface/OsuCheckbox.cs  | 17 +++++++++++++----
 .../Screens/OnlinePlay/FreeModSelectOverlay.cs  |  2 ++
 2 files changed, 15 insertions(+), 4 deletions(-)

diff --git a/osu.Game/Graphics/UserInterface/OsuCheckbox.cs b/osu.Game/Graphics/UserInterface/OsuCheckbox.cs
index 6593531099..517f83daa9 100644
--- a/osu.Game/Graphics/UserInterface/OsuCheckbox.cs
+++ b/osu.Game/Graphics/UserInterface/OsuCheckbox.cs
@@ -18,6 +18,11 @@ 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
@@ -96,10 +101,14 @@ namespace osu.Game.Graphics.UserInterface
         protected override void OnUserChange(bool value)
         {
             base.OnUserChange(value);
-            if (value)
-                sampleChecked?.Play();
-            else
-                sampleUnchecked?.Play();
+
+            if (PlaySoundsOnUserChange)
+            {
+                if (value)
+                    sampleChecked?.Play();
+                else
+                    sampleUnchecked?.Play();
+            }
         }
     }
 }
diff --git a/osu.Game/Screens/OnlinePlay/FreeModSelectOverlay.cs b/osu.Game/Screens/OnlinePlay/FreeModSelectOverlay.cs
index 628199309a..608e58b534 100644
--- a/osu.Game/Screens/OnlinePlay/FreeModSelectOverlay.cs
+++ b/osu.Game/Screens/OnlinePlay/FreeModSelectOverlay.cs
@@ -110,6 +110,8 @@ namespace osu.Game.Screens.OnlinePlay
         {
             public Action<bool> Changed;
 
+            protected override bool PlaySoundsOnUserChange => false;
+
             protected override void OnUserChange(bool value)
             {
                 base.OnUserChange(value);

From 6ff8e8dd37c3a79ea7b6c122f596272708cd6e58 Mon Sep 17 00:00:00 2001
From: smoogipoo <smoogipoo@smgi.me>
Date: Tue, 2 Feb 2021 21:29:08 +0900
Subject: [PATCH 11/11] Disable a few mods by default

---
 osu.Game/Screens/OnlinePlay/FreeModSelectOverlay.cs | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/osu.Game/Screens/OnlinePlay/FreeModSelectOverlay.cs b/osu.Game/Screens/OnlinePlay/FreeModSelectOverlay.cs
index 608e58b534..5b9a19897f 100644
--- a/osu.Game/Screens/OnlinePlay/FreeModSelectOverlay.cs
+++ b/osu.Game/Screens/OnlinePlay/FreeModSelectOverlay.cs
@@ -18,8 +18,16 @@ namespace osu.Game.Screens.OnlinePlay
     {
         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;