Fix DrawableOsuHitObject not properly cleaning up dim application callbacks

osu.Game.Rulesets.Osu/Objects/Drawables/DrawableOsuHitObject.cs

@@ -91,20 +91,35 @@ protected override void UpdateInitialTransforms()
  drawableObjectPiece.ApplyCustomUpdateState -= applyDimToDrawableHitObject;
  drawableObjectPiece.ApplyCustomUpdateState += applyDimToDrawableHitObject;
  }
- else
- applyDim(piece);
- }
 
- void applyDim(Drawable piece)
- {
- piece.FadeColour(new Color4(195, 195, 195, 255));
- using (piece.BeginDelayedSequence(InitialLifetimeOffset - OsuHitWindows.MISS_WINDOW))
- piece.FadeColour(Color4.White, 100);
+ // but at the end apply the transforms now regardless of whether this is a DHO or not.
+ // the above is just to ensure they don't get overwritten later.
+ applyDim(piece);
  }
+ }
+
+ protected override void ClearNestedHitObjects()
+ {
+ base.ClearNestedHitObjects();
+
+ // any dimmable pieces that are DHOs will be pooled separately.
+ // `applyDimToDrawableHitObject` is a closure that implicitly captures `this`,
+ // and because of separate pooling of parent and child objects, there is no guarantee that the pieces will be associated with `this` again on re-use.
+ // therefore, clean up the subscription here to avoid crosstalk.
+ // not doing so can result in the callback attempting to read things from `this` when it is in a completely bogus state (not in use or similar).
+ foreach (var piece in DimmablePieces.OfType<DrawableHitObject>())
+ piece.ApplyCustomUpdateState -= applyDimToDrawableHitObject;
+ }
 
- void applyDimToDrawableHitObject(DrawableHitObject dho, ArmedState _) => applyDim(dho);
+ private void applyDim(Drawable piece)
+ {
+ piece.FadeColour(new Color4(195, 195, 195, 255));
+ using (piece.BeginDelayedSequence(InitialLifetimeOffset - OsuHitWindows.MISS_WINDOW))
+ piece.FadeColour(Color4.White, 100);
  }
 
+ private void applyDimToDrawableHitObject(DrawableHitObject dho, ArmedState _) => applyDim(dho);
+
  protected sealed override double InitialLifetimeOffset => HitObject.TimePreempt;
 
  private OsuInputManager osuActionInputManager;