Improve performance with large numbers of panels visible

osu.Game/Screens/Select/BeatmapCarousel.cs

@@ -483,11 +483,11 @@ namespace osu.Game.Screens.Select
             {
                 DrawableCarouselItem item = Items[i];
 
+                if (!item.Item.Visible) continue;
+
                 // Only add if we're not already part of the content.
                 if (!scrollableContent.Contains(item))
                 {
-                    if (!item.Item.Visible) continue;
-
                     // Makes sure headers are always _below_ items,
                     // and depth flows downward.
                     item.Depth = i + (item is DrawableCarouselBeatmapSet ? -Items.Count : 0);

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

@@ -27,9 +27,19 @@ namespace osu.Game.Screens.Select.Carousel
 
         private CarouselItem lastSelected;
 
+        /// <summary>
+        /// To avoid overhead during filter operations, we don't attempt any selections until after all
+        /// children have been filtered. This bool will be true during the base <see cref="Filter(FilterCriteria)"/>
+        /// operation.
+        /// </summary>
+        private bool filteringChildren;
+
         public override void Filter(FilterCriteria criteria)
         {
+            filteringChildren = true;
             base.Filter(criteria);
+            filteringChildren = false;
+
             attemptSelection();
         }
 
@@ -64,6 +74,8 @@ namespace osu.Game.Screens.Select.Carousel
 
         private void attemptSelection()
         {
+            if (filteringChildren) return;
+
             // we only perform eager selection if we are a currently selected group.
             if (State != CarouselItemState.Selected) return;
 

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

@@ -33,7 +33,8 @@ namespace osu.Game.Screens.Select.Carousel
 
                 if (InternalChildren != null)
                     foreach (var c in InternalChildren)
-                        items.AddRange(c.Drawables);
+                        // if (!c.Filtered) <- potential optimisation at the cost of no fade out animations.
+                            items.AddRange(c.Drawables);
 
                 return items;
             }