Fix per-frame allocations in BeatmapCarousel

osu.Game/Overlays/NotificationOverlayToastTray.cs

@@ -153,8 +153,22 @@ protected override void Update()
         {
             base.Update();
 
-            float height = toastFlow.Count > 0 ? toastFlow.DrawHeight + 120 : 0;
-            float alpha = toastFlow.Count > 0 ? MathHelper.Clamp(toastFlow.DrawHeight / 41, 0, 1) * toastFlow.Children.Max(n => n.Alpha) : 0;
+            float height = 0;
+            float alpha = 0;
+
+            if (toastFlow.Count > 0)
+            {
+                float maxNotificationAlpha = 0;
+
+                foreach (var t in toastFlow)
+                {
+                    if (t.Alpha > maxNotificationAlpha)
+                        maxNotificationAlpha = t.Alpha;
+                }
+
+                height = toastFlow.DrawHeight + 120;
+                alpha = MathHelper.Clamp(toastFlow.DrawHeight / 41, 0, 1) * maxNotificationAlpha;
+            }
 
             toastContentBackground.Height = (float)Interpolation.DampContinuously(toastContentBackground.Height, height, 10, Clock.ElapsedFrameTime);
             toastContentBackground.Alpha = (float)Interpolation.DampContinuously(toastContentBackground.Alpha, alpha, 10, Clock.ElapsedFrameTime);

osu.Game/Screens/Select/BeatmapCarousel.cs

@@ -857,8 +857,9 @@ protected override void Update()
                     // Add those items within the previously found index range that should be displayed.
                     foreach (var item in toDisplay)
                     {
-                        var panel = setPool.Get(p => p.Item = item);
+                        var panel = setPool.Get();
 
+                        panel.Item = item;
                         panel.Y = item.CarouselYPosition;
 
                         Scroll.Add(panel);
@@ -900,8 +901,8 @@ protected override void Update()
 
                 if (item is DrawableCarouselBeatmapSet set)
                 {
-                    foreach (var diff in set.DrawableBeatmaps)
-                        updateItem(diff, item);
+                    for (int i = 0; i < set.DrawableBeatmaps.Count; i++)
+                        updateItem(set.DrawableBeatmaps[i], item);
                 }
             }
         }
@@ -1101,7 +1102,7 @@ private static float offsetX(float dist, float halfHeight)
         }
 
         /// <summary>
-        /// Update a item's x position and multiplicative alpha based on its y position and
+        /// Update an item's x position and multiplicative alpha based on its y position and
         /// the current scroll position.
         /// </summary>
         /// <param name="item">The item to be updated.</param>

osu.Game/Screens/Select/Carousel/DrawableCarouselBeatmapSet.cs

@@ -51,7 +51,7 @@ public partial class DrawableCarouselBeatmapSet : DrawableCarouselItem, IHasCont
         [Resolved]
         private IBindable<RulesetInfo> ruleset { get; set; } = null!;
 
-        public IEnumerable<DrawableCarouselItem> DrawableBeatmaps => beatmapContainer?.IsLoaded != true ? Enumerable.Empty<DrawableCarouselItem>() : beatmapContainer.AliveChildren;
+        public IReadOnlyList<DrawableCarouselItem> DrawableBeatmaps => beatmapContainer?.IsLoaded != true ? Array.Empty<DrawableCarouselItem>() : beatmapContainer;
 
         private Container<DrawableCarouselItem>? beatmapContainer;