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Fixed in 2021.2.X

Fixed in 2021.1.X

Votes

0

Found in

2019.4.3f1

Issue ID

1266460

Regression

No

Composite Collider doesn't work with PolygonCollider2D with inverted scale.

Physics2D

-

How to reproduce:
1. Open the attached project (case_1266460-CompositeColliderWindingIssue.zip)
2. Open the "SampleScene" Scene
3. Select the "Composite" GameObject.
4. Each child GameObject has a BoxCollider2D set to use the composite. One has scale (1,1,1) and the other has scale (-1,1,1). This causes opposite windings.

Expected result: The two boxes should merge together producing a single outline (no hole in the center)
Actual result: The two boxes merge together but don't produce the single output as they have a hole in the center.

The original projects GameObjects also show this but not as clear. The bad behaviour becomes one where the two shapes end up being subtracted from one another in an XOR operation rather than a UNION (OR) operation. NOTE: When checking those GameObjects they will appear to be broken still. This is because the CompositeCollider2D stores the previous calculation. To force a new calculation with the fix, you have to disable/enable the GameObject with the CompositeCollider2D on it.

When a PolygonCollider2D is added to a CompositeCollider2D and it has either its X or Y (not both) axis-sign opposite then this changes the winding of the polygon paths from anti-clockwise to anti-clockwise.

  1. Response avatar

    Resolution Note (fix version 2021.2):

    Using opposing axis scales was causing the winding order to change for the PolygonCollider2D paths. This meant the CompositeCollider2D interpreted them as internal holes when merging. Fixed the winding to be consistent in such cases.

    NOTE: To apply this fix to existing CompositeCollider2D geometry, the CompositeCollider2D GameObject will need to be disabled/enabled to trigger it recalculating all geometry. This is because the composite stores the geometry for performance reasons.

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