From f156cb797df13c31e43856e58037cec9b490bf7d Mon Sep 17 00:00:00 2001
From: Dean Herbert <pe@ppy.sh>
Date: Tue, 5 Apr 2022 16:40:09 +0900
Subject: [PATCH] Improve nested scroll behaviour

---
 osu.Game/Overlays/Mods/ModColumn.cs       | 60 ++++++++++++++++++++++-
 osu.Game/Overlays/Mods/ModSelectScreen.cs |  1 +
 2 files changed, 60 insertions(+), 1 deletion(-)

diff --git a/osu.Game/Overlays/Mods/ModColumn.cs b/osu.Game/Overlays/Mods/ModColumn.cs
index 46a562ac98..513dd2ca3f 100644
--- a/osu.Game/Overlays/Mods/ModColumn.cs
+++ b/osu.Game/Overlays/Mods/ModColumn.cs
@@ -151,9 +151,10 @@ namespace osu.Game.Overlays.Mods
                                     },
                                     new Drawable[]
                                     {
-                                        new OsuScrollContainer
+                                        new NestedVerticalScrollContainer
                                         {
                                             RelativeSizeAxes = Axes.Both,
+                                            ClampExtension = 100,
                                             ScrollbarOverlapsContent = false,
                                             Child = panelFlow = new FillFlowContainer<ModPanel>
                                             {
@@ -194,6 +195,63 @@ namespace osu.Game.Overlays.Mods
             }
         }
 
+        /// <summary>
+        /// A scroll container that handles the case of vertically scrolling content inside a larger horizontally scrolling parent container.
+        /// </summary>
+        private class NestedVerticalScrollContainer : OsuScrollContainer
+        {
+            private OsuScrollContainer? parentScrollContainer;
+
+            protected override void LoadComplete()
+            {
+                base.LoadComplete();
+
+                parentScrollContainer = findClosestParent<OsuScrollContainer>();
+            }
+
+            protected override bool OnScroll(ScrollEvent e)
+            {
+                if (parentScrollContainer == null)
+                    return base.OnScroll(e);
+
+                // If not on screen, handle scroll but also allow parent to scroll at the same time.
+                bool topRightOutsideOfView = parentScrollContainer.ScreenSpaceDrawQuad.Contains(ScreenSpaceDrawQuad.TopRight) == false;
+                bool bottomLeftOutsideOfView = parentScrollContainer.ScreenSpaceDrawQuad.Contains(ScreenSpaceDrawQuad.BottomLeft) == false;
+
+                if (topRightOutsideOfView || bottomLeftOutsideOfView)
+                {
+                    base.OnScroll(e);
+                    return false;
+                }
+
+                bool scrollingPastEnd = e.ScrollDelta.Y < 0 && IsScrolledToEnd();
+                bool scrollingPastStart = e.ScrollDelta.Y > 0 && Target <= 0;
+
+                // Same deal if at one of the two extents of the view.
+                if (scrollingPastStart || scrollingPastEnd)
+                {
+                    base.OnScroll(e);
+                    return false;
+                }
+
+                return base.OnScroll(e);
+            }
+
+            // TODO: remove when https://github.com/ppy/osu-framework/pull/5092 is available.
+            private T? findClosestParent<T>() where T : class, IDrawable
+            {
+                Drawable cursor = this;
+
+                while ((cursor = cursor.Parent) != null)
+                {
+                    if (cursor is T match)
+                        return match;
+                }
+
+                return default;
+            }
+        }
+
         private void createHeaderText()
         {
             IEnumerable<string> headerTextWords = ModType.Humanize(LetterCasing.Title).Split(' ');
diff --git a/osu.Game/Overlays/Mods/ModSelectScreen.cs b/osu.Game/Overlays/Mods/ModSelectScreen.cs
index 5197cb6c3e..1d6f784133 100644
--- a/osu.Game/Overlays/Mods/ModSelectScreen.cs
+++ b/osu.Game/Overlays/Mods/ModSelectScreen.cs
@@ -106,6 +106,7 @@ namespace osu.Game.Overlays.Mods
                                             {
                                                 RelativeSizeAxes = Axes.Both,
                                                 Masking = false,
+                                                ClampExtension = 100,
                                                 ScrollbarOverlapsContent = false,
                                                 Child = columnFlow = new ModColumnContainer
                                                 {