Remove ScrollableContent container from carousel

This was causing multiple issues with masking and sizing and really
didn't need to exist in the first place. Also not sure why the pool was
nested inside the scroll container, but it isn't any more. Probably for
the best.

osu.Game.Tests/Visual/SongSelect/TestSceneBeatmapCarousel.cs

@@ -917,7 +917,7 @@ namespace osu.Game.Tests.Visual.SongSelect
             {
                 get
                 {
-                    foreach (var item in ScrollableContent)
+                    foreach (var item in Scroll.Children)
                     {
                         yield return item;
 

osu.Game/Screens/Select/BeatmapCarousel.cs

@@ -91,7 +91,7 @@ namespace osu.Game.Screens.Select
         /// </summary>
         public bool BeatmapSetsLoaded { get; private set; }
 
-        private readonly CarouselScrollContainer scroll;
+        protected readonly CarouselScrollContainer Scroll;
 
         private IEnumerable<CarouselBeatmapSet> beatmapSets => root.Children.OfType<CarouselBeatmapSet>();
 
@@ -112,7 +112,7 @@ namespace osu.Game.Screens.Select
             if (selectedBeatmapSet != null && !beatmapSets.Contains(selectedBeatmapSet.BeatmapSet))
                 selectedBeatmapSet = null;
 
-            ScrollableContent.Clear(false);
+            Scroll.Clear(false);
             itemsCache.Invalidate();
             scrollPositionCache.Invalidate();
 
@@ -132,8 +132,6 @@ namespace osu.Game.Screens.Select
         private readonly Cached itemsCache = new Cached();
         private readonly Cached scrollPositionCache = new Cached();
 
-        protected readonly Container<DrawableCarouselItem> ScrollableContent;
-
         public Bindable<bool> RightClickScrollingEnabled = new Bindable<bool>();
 
         public Bindable<RandomSelectAlgorithm> RandomAlgorithm = new Bindable<RandomSelectAlgorithm>();
@@ -155,17 +153,12 @@ namespace osu.Game.Screens.Select
             InternalChild = new OsuContextMenuContainer
             {
                 RelativeSizeAxes = Axes.Both,
-                Child = scroll = new CarouselScrollContainer
+                Children = new Drawable[]
                 {
-                    Masking = false,
+                    setPool,
-                    RelativeSizeAxes = Axes.Both,
+                    Scroll = new CarouselScrollContainer
-                    Children = new Drawable[]
                     {
-                        setPool,
+                        RelativeSizeAxes = Axes.Both,
-                        ScrollableContent = new Container<DrawableCarouselItem>
-                        {
-                            RelativeSizeAxes = Axes.X,
-                        }
                     }
                 }
             };
@@ -180,7 +173,7 @@ namespace osu.Game.Screens.Select
             config.BindWith(OsuSetting.RandomSelectAlgorithm, RandomAlgorithm);
             config.BindWith(OsuSetting.SongSelectRightMouseScroll, RightClickScrollingEnabled);
 
-            RightClickScrollingEnabled.ValueChanged += enabled => scroll.RightMouseScrollbar = enabled.NewValue;
+            RightClickScrollingEnabled.ValueChanged += enabled => Scroll.RightMouseScrollbar = enabled.NewValue;
             RightClickScrollingEnabled.TriggerChange();
 
             itemUpdated = beatmaps.ItemUpdated.GetBoundCopy();
@@ -421,12 +414,12 @@ namespace osu.Game.Screens.Select
         /// <summary>
         /// The position of the lower visible bound with respect to the current scroll position.
         /// </summary>
-        private float visibleBottomBound => scroll.Current + DrawHeight + BleedBottom;
+        private float visibleBottomBound => Scroll.Current + DrawHeight + BleedBottom;
 
         /// <summary>
         /// The position of the upper visible bound with respect to the current scroll position.
         /// </summary>
-        private float visibleUpperBound => scroll.Current - BleedTop;
+        private float visibleUpperBound => Scroll.Current - BleedTop;
 
         public void FlushPendingFilterOperations()
         {
@@ -468,7 +461,7 @@ namespace osu.Game.Screens.Select
                 root.Filter(activeCriteria);
                 itemsCache.Invalidate();
 
-                if (alwaysResetScrollPosition || !scroll.UserScrolling)
+                if (alwaysResetScrollPosition || !Scroll.UserScrolling)
                     ScrollToSelected();
             }
         }
@@ -594,7 +587,7 @@ namespace osu.Game.Screens.Select
                 {
                     var toDisplay = visibleItems.GetRange(displayedRange.first, displayedRange.last - displayedRange.first + 1);
 
-                    foreach (var panel in ScrollableContent.Children)
+                    foreach (var panel in Scroll.Children)
                     {
                         if (toDisplay.Remove(panel.Item))
                         {
@@ -620,7 +613,7 @@ namespace osu.Game.Screens.Select
                         panel.Depth = item.CarouselYPosition;
                         panel.Y = item.CarouselYPosition;
 
-                        ScrollableContent.Add(panel);
+                        Scroll.Add(panel);
                     }
                 }
             }
@@ -637,7 +630,7 @@ namespace osu.Game.Screens.Select
 
             // Update externally controlled state of currently visible items (e.g. x-offset and opacity).
             // This is a per-frame update on all drawable panels.
-            foreach (DrawableCarouselItem item in ScrollableContent.Children)
+            foreach (DrawableCarouselItem item in Scroll.Children)
             {
                 updateItem(item);
 
@@ -789,7 +782,8 @@ namespace osu.Game.Screens.Select
             }
 
             currentY += visibleHalfHeight;
-            ScrollableContent.Height = currentY;
+
+            Scroll.ScrollContent.Height = currentY;
 
             if (BeatmapSetsLoaded && (selectedBeatmapSet == null || selectedBeatmap == null || selectedBeatmapSet.State.Value != CarouselItemState.Selected))
             {
@@ -809,7 +803,7 @@ namespace osu.Game.Screens.Select
                 if (firstScroll)
                 {
                     // reduce movement when first displaying the carousel.
-                    scroll.ScrollTo(scrollTarget.Value - 200, false);
+                    Scroll.ScrollTo(scrollTarget.Value - 200, false);
                     firstScroll = false;
                 }
 
@@ -844,7 +838,7 @@ namespace osu.Game.Screens.Select
         /// <param name="parent">For nested items, the parent of the item to be updated.</param>
         private void updateItem(DrawableCarouselItem item, DrawableCarouselItem parent = null)
         {
-            Vector2 posInScroll = ScrollableContent.ToLocalSpace(item.Header.ScreenSpaceDrawQuad.Centre);
+            Vector2 posInScroll = Scroll.ScrollContent.ToLocalSpace(item.Header.ScreenSpaceDrawQuad.Centre);
             float itemDrawY = posInScroll.Y - visibleUpperBound;
             float dist = Math.Abs(1f - itemDrawY / visibleHalfHeight);
 
@@ -889,7 +883,7 @@ namespace osu.Game.Screens.Select
             }
         }
 
-        private class CarouselScrollContainer : OsuScrollContainer
+        protected class CarouselScrollContainer : OsuScrollContainer<DrawableCarouselItem>
         {
             private bool rightMouseScrollBlocked;
 
@@ -898,6 +892,12 @@ namespace osu.Game.Screens.Select
             /// </summary>
             public bool UserScrolling { get; private set; }
 
+            public CarouselScrollContainer()
+            {
+                // size is determined by the carousel itself, due to not all content necessarily being loaded.
+                ScrollContent.AutoSizeAxes = Axes.None;
+            }
+
             // ReSharper disable once OptionalParameterHierarchyMismatch 2020.3 EAP4 bug. (https://youtrack.jetbrains.com/issue/RSRP-481535?p=RIDER-51910)
             protected override void OnUserScroll(float value, bool animated = true, double? distanceDecay = default)
             {