Improve the feel of hovering toolbox component items

osu.Game/Overlays/SkinEditor/SkinComponentToolbox.cs

@@ -2,12 +2,13 @@
 // See the LICENCE file in the repository root for full licence text.
 
 using System;
+using System.Linq;
 using osu.Framework.Allocation;
 using osu.Framework.Graphics;
 using osu.Framework.Graphics.Containers;
 using osu.Framework.Input.Events;
 using osu.Framework.Logging;
-using osu.Game.Graphics;
+using osu.Framework.Threading;
 using osu.Game.Graphics.Sprites;
 using osu.Game.Graphics.UserInterface;
 using osu.Game.Localisation;
@@ -65,7 +66,8 @@ namespace osu.Game.Overlays.SkinEditor
 
                 fill.Add(new ToolboxComponentButton(instance, target)
                 {
-                    RequestPlacement = t => RequestPlacement?.Invoke(t)
+                    RequestPlacement = t => RequestPlacement?.Invoke(t),
+                    Expanding = contractOtherButtons,
                 });
             }
             catch (DependencyNotRegisteredException)
@@ -79,15 +81,29 @@ namespace osu.Game.Overlays.SkinEditor
             }
         }
 
+        private void contractOtherButtons(ToolboxComponentButton obj)
+        {
+            foreach (var b in fill.OfType<ToolboxComponentButton>())
+            {
+                if (b == obj)
+                    continue;
+
+                b.Contract();
+            }
+        }
+
         public partial class ToolboxComponentButton : OsuButton
         {
             public Action<Type>? RequestPlacement;
+            public Action<ToolboxComponentButton>? Expanding;
 
             private readonly Drawable component;
             private readonly CompositeDrawable? dependencySource;
 
             private Container innerContainer = null!;
 
+            private ScheduledDelegate? expandContractAction;
+
             private const float contracted_size = 60;
             private const float expanded_size = 120;
 
@@ -102,20 +118,44 @@ namespace osu.Game.Overlays.SkinEditor
                 Height = contracted_size;
             }
 
+            private const double animation_duration = 500;
+
             protected override bool OnHover(HoverEvent e)
             {
-                this.Delay(300).ResizeHeightTo(expanded_size, 500, Easing.OutQuint);
+                expandContractAction = Scheduler.AddDelayed(() =>
+                {
+                    this.ResizeHeightTo(expanded_size, animation_duration, Easing.OutQuint);
+                    Expanding?.Invoke(this);
+                }, 100);
+
                 return base.OnHover(e);
             }
 
             protected override void OnHoverLost(HoverLostEvent e)
             {
                 base.OnHoverLost(e);
-                this.ResizeHeightTo(contracted_size, 500, Easing.OutQuint);
+
+                expandContractAction?.Cancel();
+                // If no other component is selected for too long, force a contract.
+                // Otherwise we will generally contract when Contract() is called from outside.
+                expandContractAction = Scheduler.AddDelayed(Contract, 1000);
+            }
+
+            public void Contract()
+            {
+                // Cheap debouncing to avoid stacking animations.
+                // The only place this is nulled is at the end of this method.
+                if (expandContractAction == null)
+                    return;
+
+                this.ResizeHeightTo(contracted_size, animation_duration, Easing.OutQuint);
+
+                expandContractAction?.Cancel();
+                expandContractAction = null;
             }
 
             [BackgroundDependencyLoader]
-            private void load(OverlayColourProvider colourProvider, OsuColour colours)
+            private void load(OverlayColourProvider colourProvider)
             {
                 BackgroundColour = colourProvider.Background3;