Some fruits on the platter randomly disappear when an explosion happens at the end of a combo

[nagi-desuuu]

Type

Cosmetic

Bug description

I've seen it happen first while I was playing Alt Futur where the last fruit of a catch combo disappears right before the explosion of the fruits inside the platter, so I decided to try this on other maps too.

Screenshots or videos

osu.2024-08-07.16-56-01.mp4

osu.2024-08-07.17-30-42.mp4

Also replicable on built-in skins

osu.2024-08-07.17-35-04.mp4

Version

2024.731.0

Logs

1723022597.network.log
1723022597.performance.log
1723022597.runtime.log
1723022597.updater.log
1723022598.nauth.log
1723022597.auth.log

(For some reason, my logs weren't being exported when I hit the export logs button, but that could just be me)

[smoogipoo]

I've done some preliminary investigation into this, and it looks to be because hitobjects are removed from their parenting container prior to their state being copied over to a new representation (for the purpose of being dropped), leading to things like DrawPosition being incorrectly calculated.

A simple demonstrative fix is the following:

diff --git a/osu.Game.Rulesets.Catch.Tests/TestSceneCatcher.cs b/osu.Game.Rulesets.Catch.Tests/TestSceneCatcher.cs
index b03fa00f76..6f62fc2742 100644
--- a/osu.Game.Rulesets.Catch.Tests/TestSceneCatcher.cs
+++ b/osu.Game.Rulesets.Catch.Tests/TestSceneCatcher.cs
@@ -57,6 +57,21 @@ public partial class TestSceneCatcher : OsuTestScene
             };
         });

+        [Test]
+        [Solo]
+        public void TestWangs()
+        {
+            AddStep("catch normal fruit", () =>
+            {
+                attemptCatch(new Fruit());
+            });
+
+            AddStep("catch normal fruit", () =>
+            {
+                attemptCatch(new Fruit { IndexInBeatmap = 2, LastInCombo = true });
+            });
+        }
+
         [Test]
         public void TestCatcherHyperStateReverted()
         {
diff --git a/osu.Game.Rulesets.Catch/UI/Catcher.cs b/osu.Game.Rulesets.Catch/UI/Catcher.cs
index dca01fc61a..4c0dafe2de 100644
--- a/osu.Game.Rulesets.Catch/UI/Catcher.cs
+++ b/osu.Game.Rulesets.Catch/UI/Catcher.cs
@@ -427,11 +427,10 @@ private void clearPlate(DroppedObjectAnimation animation)
         {
             var caughtObjects = caughtObjectContainer.Children.ToArray();

-            caughtObjectContainer.Clear(false);
-
             // Use the already returned PoolableDrawables for new objects
             var droppedObjects = caughtObjects.Select(getDroppedObject).ToArray();

+            caughtObjectContainer.Clear(false);
             droppedObjectTarget.AddRange(droppedObjects);

             foreach (var droppedObject in droppedObjects)

However, take note of the comment.

I still have questions - haven't pieced together the entire puzzle:

1. Why is DrawPosition getting affected? CaughtObject isn't using relative position.
2. Why is the fruit representation (in the test - whether it's green or red) affected? If, rather than the above diff, copy just the position from before the Clear() across, then both hitobjects in the test will be green.