From 5b24800b0e9c88af8747f9e33a3c14b97ca1f4d8 Mon Sep 17 00:00:00 2001
From: Dean Herbert <pe@ppy.sh>
Date: Fri, 21 Jan 2022 12:37:17 +0900
Subject: [PATCH 1/2] Avoid applying filter in `UpdateBeatmapSet` flow

---
 osu.Game/Screens/Select/BeatmapCarousel.cs    | 12 +++++----
 .../Screens/Select/Carousel/CarouselGroup.cs  | 27 +++++++++++++++++--
 2 files changed, 32 insertions(+), 7 deletions(-)

diff --git a/osu.Game/Screens/Select/BeatmapCarousel.cs b/osu.Game/Screens/Select/BeatmapCarousel.cs
index 75ad0511e6..6d3d7aa185 100644
--- a/osu.Game/Screens/Select/BeatmapCarousel.cs
+++ b/osu.Game/Screens/Select/BeatmapCarousel.cs
@@ -300,16 +300,18 @@ namespace osu.Game.Screens.Select
 
             root.AddChild(newSet);
 
-            // only reset scroll position if already near the scroll target.
-            // without this, during a large beatmap import it is impossible to navigate the carousel.
-            applyActiveCriteria(false, alwaysResetScrollPosition: false);
-
             // check if we can/need to maintain our current selection.
             if (previouslySelectedID != null)
                 select((CarouselItem)newSet.Beatmaps.FirstOrDefault(b => b.BeatmapInfo.ID == previouslySelectedID) ?? newSet);
 
             itemsCache.Invalidate();
-            Schedule(() => BeatmapSetsChanged?.Invoke());
+            Schedule(() =>
+            {
+                if (!Scroll.UserScrolling)
+                    ScrollToSelected(true);
+
+                BeatmapSetsChanged?.Invoke();
+            });
         });
 
         /// <summary>
diff --git a/osu.Game/Screens/Select/Carousel/CarouselGroup.cs b/osu.Game/Screens/Select/Carousel/CarouselGroup.cs
index b85e868b89..7e4c5fad72 100644
--- a/osu.Game/Screens/Select/Carousel/CarouselGroup.cs
+++ b/osu.Game/Screens/Select/Carousel/CarouselGroup.cs
@@ -3,6 +3,7 @@
 
 using System.Collections.Generic;
 using System.Linq;
+using JetBrains.Annotations;
 
 namespace osu.Game.Screens.Select.Carousel
 {
@@ -36,7 +37,21 @@ namespace osu.Game.Screens.Select.Carousel
         {
             i.State.ValueChanged += state => ChildItemStateChanged(i, state.NewValue);
             i.ChildID = ++currentChildID;
-            InternalChildren.Add(i);
+
+            if (lastCriteria != null)
+            {
+                i.Filter(lastCriteria);
+
+                int index = InternalChildren.BinarySearch(i, criteriaComparer);
+                if (index < 0) index = ~index; // BinarySearch hacks multiple return values with 2's complement.
+
+                InternalChildren.Insert(index, i);
+            }
+            else
+            {
+                // criteria may be null for initial population. the filtering will be applied post-add.
+                InternalChildren.Add(i);
+            }
         }
 
         public CarouselGroup(List<CarouselItem> items = null)
@@ -62,14 +77,22 @@ namespace osu.Game.Screens.Select.Carousel
             };
         }
 
+        private Comparer<CarouselItem> criteriaComparer;
+
+        [CanBeNull]
+        private FilterCriteria lastCriteria;
+
         public override void Filter(FilterCriteria criteria)
         {
             base.Filter(criteria);
 
             InternalChildren.ForEach(c => c.Filter(criteria));
+
             // IEnumerable<T>.OrderBy() is used instead of List<T>.Sort() to ensure sorting stability
-            var criteriaComparer = Comparer<CarouselItem>.Create((x, y) => x.CompareTo(criteria, y));
+            criteriaComparer = Comparer<CarouselItem>.Create((x, y) => x.CompareTo(criteria, y));
             InternalChildren = InternalChildren.OrderBy(c => c, criteriaComparer).ToList();
+
+            lastCriteria = criteria;
         }
 
         protected virtual void ChildItemStateChanged(CarouselItem item, CarouselItemState value)

From bed7b69464ed1b6971ae84ee81885d6ce90c5fed Mon Sep 17 00:00:00 2001
From: Dean Herbert <pe@ppy.sh>
Date: Fri, 21 Jan 2022 13:09:03 +0900
Subject: [PATCH 2/2] Apply NRT to `CarouselGroup`

---
 .../Screens/Select/Carousel/CarouselGroup.cs     | 16 ++++++++--------
 1 file changed, 8 insertions(+), 8 deletions(-)

diff --git a/osu.Game/Screens/Select/Carousel/CarouselGroup.cs b/osu.Game/Screens/Select/Carousel/CarouselGroup.cs
index 7e4c5fad72..6ebe314072 100644
--- a/osu.Game/Screens/Select/Carousel/CarouselGroup.cs
+++ b/osu.Game/Screens/Select/Carousel/CarouselGroup.cs
@@ -3,7 +3,8 @@
 
 using System.Collections.Generic;
 using System.Linq;
-using JetBrains.Annotations;
+
+#nullable enable
 
 namespace osu.Game.Screens.Select.Carousel
 {
@@ -12,7 +13,7 @@ namespace osu.Game.Screens.Select.Carousel
     /// </summary>
     public class CarouselGroup : CarouselItem
     {
-        public override DrawableCarouselItem CreateDrawableRepresentation() => null;
+        public override DrawableCarouselItem? CreateDrawableRepresentation() => null;
 
         public IReadOnlyList<CarouselItem> Children => InternalChildren;
 
@@ -24,6 +25,10 @@ namespace osu.Game.Screens.Select.Carousel
         /// </summary>
         private ulong currentChildID;
 
+        private Comparer<CarouselItem>? criteriaComparer;
+
+        private FilterCriteria? lastCriteria;
+
         public virtual void RemoveChild(CarouselItem i)
         {
             InternalChildren.Remove(i);
@@ -54,7 +59,7 @@ namespace osu.Game.Screens.Select.Carousel
             }
         }
 
-        public CarouselGroup(List<CarouselItem> items = null)
+        public CarouselGroup(List<CarouselItem>? items = null)
         {
             if (items != null) InternalChildren = items;
 
@@ -77,11 +82,6 @@ namespace osu.Game.Screens.Select.Carousel
             };
         }
 
-        private Comparer<CarouselItem> criteriaComparer;
-
-        [CanBeNull]
-        private FilterCriteria lastCriteria;
-
         public override void Filter(FilterCriteria criteria)
         {
             base.Filter(criteria);