Add basic selection support

osu.Game/Screens/SelectV2/BeatmapCarouselV2.cs

@@ -14,6 +14,7 @@ using osu.Framework.Extensions.Color4Extensions;
 using osu.Framework.Graphics;
 using osu.Framework.Graphics.Pooling;
 using osu.Framework.Graphics.Shapes;
+using osu.Framework.Input.Events;
 using osu.Game.Beatmaps;
 using osu.Game.Database;
 using osu.Game.Graphics.Sprites;
@@ -23,6 +24,7 @@ using osuTK.Graphics;
 
 namespace osu.Game.Screens.SelectV2
 {
+    [Cached]
     public partial class BeatmapCarouselV2 : Carousel
     {
         private IBindableList<BeatmapSetInfo> detachedBeatmaps = null!;
@@ -102,7 +104,48 @@ namespace osu.Game.Screens.SelectV2
 
     public partial class BeatmapCarouselPanel : PoolableDrawable, ICarouselPanel
     {
-        public CarouselItem? Item { get; set; }
+        [Resolved]
+        private BeatmapCarouselV2 carousel { get; set; } = null!;
+
+        public CarouselItem? Item
+        {
+            get => item;
+            set
+            {
+                item = value;
+
+                selected.UnbindBindings();
+
+                if (item != null)
+                    selected.BindTo(item.Selected);
+            }
+        }
+
+        private readonly BindableBool selected = new BindableBool();
+        private CarouselItem? item;
+
+        [BackgroundDependencyLoader]
+        private void load()
+        {
+            selected.BindValueChanged(value =>
+            {
+                if (value.NewValue)
+                {
+                    BorderThickness = 5;
+                    BorderColour = Color4.Pink;
+                }
+                else
+                {
+                    BorderThickness = 0;
+                }
+            });
+        }
+
+        protected override void FreeAfterUse()
+        {
+            base.FreeAfterUse();
+            Item = null;
+        }
 
         protected override void PrepareForUse()
         {
@@ -111,6 +154,7 @@ namespace osu.Game.Screens.SelectV2
             Debug.Assert(Item != null);
 
             Size = new Vector2(500, Item.DrawHeight);
+            Masking = true;
 
             InternalChildren = new Drawable[]
             {
@@ -128,6 +172,12 @@ namespace osu.Game.Screens.SelectV2
                 }
             };
         }
+
+        protected override bool OnClick(ClickEvent e)
+        {
+            carousel.CurrentSelection = Item!.Model;
+            return true;
+        }
     }
 
     public class BeatmapCarouselItem : CarouselItem
@@ -165,7 +215,7 @@ namespace osu.Game.Screens.SelectV2
 
             CarouselItem? lastItem = null;
 
-            var newItems = new List<CarouselItem>();
+            var newItems = new List<CarouselItem>(items.Count());
 
             foreach (var item in items)
             {

osu.Game/Screens/SelectV2/Carousel.cs

@@ -77,8 +77,28 @@ namespace osu.Game.Screens.SelectV2
         /// All items which are to be considered for display in this carousel.
         /// Mutating this list will automatically queue a <see cref="QueueFilter"/>.
         /// </summary>
+        /// <remarks>
+        /// Note that an <see cref="ICarouselFilter"/> may add new items which are displayed but not tracked in this list.
+        /// </remarks>
         protected readonly BindableList<CarouselItem> Items = new BindableList<CarouselItem>();
 
+        /// <summary>
+        /// The currently selected model.
+        /// </summary>
+        /// <remarks>
+        /// Setting this will ensure <see cref="CarouselItem.Selected"/> is set to <c>true</c> only on the matching <see cref="CarouselItem"/>.
+        /// Of note, if no matching item exists all items will be deselected while waiting for potential new item which matches.
+        /// </remarks>
+        public virtual object? CurrentSelection
+        {
+            get => currentSelection;
+            set
+            {
+                currentSelection = value;
+                updateSelection();
+            }
+        }
+
         private List<CarouselItem>? displayedCarouselItems;
 
         private readonly DoublePrecisionScroll scroll;
@@ -169,6 +189,8 @@ namespace osu.Game.Screens.SelectV2
             displayedCarouselItems = items.ToList();
             displayedRange = null;
 
+            updateSelection();
+
             void log(string text) => Logger.Log($"Carousel[op {cts.GetHashCode().ToString().Substring(0, 5)}] {stopwatch.ElapsedMilliseconds} ms: {text}");
         }
 
@@ -186,6 +208,24 @@ namespace osu.Game.Screens.SelectV2
 
         #endregion
 
+        #region Selection handling
+
+        private object? currentSelection;
+
+        private void updateSelection()
+        {
+            if (displayedCarouselItems == null) return;
+
+            // TODO: this is ugly, we probably should stop exposing CarouselItem externally.
+            foreach (var item in Items)
+                item.Selected.Value = item.Model == currentSelection;
+
+            foreach (var item in displayedCarouselItems)
+                item.Selected.Value = item.Model == currentSelection;
+        }
+
+        #endregion
+
         #region Display handling
 
         private DisplayRange? displayedRange;

osu.Game/Screens/SelectV2/CarouselItem.cs

@@ -2,22 +2,25 @@
 // See the LICENCE file in the repository root for full licence text.
 
 using System;
+using osu.Framework.Bindables;
 
 namespace osu.Game.Screens.SelectV2
 {
     /// <summary>
-    /// Represents a single display item for display in a <see cref="Carousel"/>.
+    /// Represents a single display item for display in a <see cref="Carousel{T}"/>.
     /// This is used to house information related to the attached model that helps with display and tracking.
     /// </summary>
     public abstract class CarouselItem : IComparable<CarouselItem>
     {
+        public readonly BindableBool Selected = new BindableBool();
+
         /// <summary>
         /// The model this item is representing.
         /// </summary>
         public readonly object Model;
 
         /// <summary>
-        /// The current Y position in the carousel. This is managed by <see cref="Carousel"/> and should not be set manually.
+        /// The current Y position in the carousel. This is managed by <see cref="Carousel{T}"/> and should not be set manually.
         /// </summary>
         public double CarouselYPosition { get; set; }
 

osu.Game/Screens/SelectV2/ICarouselFilter.cs

@@ -8,7 +8,7 @@ using System.Threading.Tasks;
 namespace osu.Game.Screens.SelectV2
 {
     /// <summary>
-    /// An interface representing a filter operation which can be run on a <see cref="Carousel"/>.
+    /// An interface representing a filter operation which can be run on a <see cref="Carousel{T}"/>.
     /// </summary>
     public interface ICarouselFilter
     {

osu.Game/Screens/SelectV2/ICarouselPanel.cs

@@ -6,7 +6,7 @@ using osu.Framework.Graphics;
 namespace osu.Game.Screens.SelectV2
 {
     /// <summary>
-    /// An interface to be attached to any <see cref="Drawable"/>s which are used for display inside a <see cref="Carousel"/>.
+    /// An interface to be attached to any <see cref="Drawable"/>s which are used for display inside a <see cref="Carousel{T}"/>.
     /// </summary>
     public interface ICarouselPanel
     {
@@ -16,7 +16,7 @@ namespace osu.Game.Screens.SelectV2
         double YPosition => Item!.CarouselYPosition;
 
         /// <summary>
-        /// The carousel item this drawable is representing. This is managed by <see cref="Carousel"/> and should not be set manually.
+        /// The carousel item this drawable is representing. This is managed by <see cref="Carousel{T}"/> and should not be set manually.
         /// </summary>
         CarouselItem? Item { get; set; }
     }