MatterJS bodies produce incorrect collisions with negative scale
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- Dominant language
- JavaScript
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Description
Version
- Phaser Version: 3.90
- Operating system: Windows
- Browser: Chrome/Firefox
Description
When a MatterJS body has its scale set to -1, the detected collisions have supports that seem to always just clamp directly to the shape's vertices instead of where the collision occurred. This appears to be a bug with MatterJS as a whole, as I was able to reproduce it using exclusively MatterJS, but it appears MatterJS is pretty much unmaintained and Phaser has its own implementation of MatterJS built in anyways so I figured it would be better to open the issue here.
Example Test Code
https://codesandbox.io/p/sandbox/rsy4lz
Click to drop a rectangle on top of the pentagon; red dots will appear at the collision. Click the button at the top to invert the scale X of the pentagon to see the red dots will not appear at the collision anymore.
Additional Information
Contributor guide
First steps
- Read the whole issue, then the project's contributing guide.
- Comment on the issue to say you are picking it up — it saves two people doing the same work.
- Fork the repository and make your change on a branch.
- Open a pull request that references the issue number.
Research direction
Start by running the linked CodeSandbox reproduction with Phaser 3.90 and compare collision supports before and after inverting the pentagon's X scale. Trace the MatterJS collision handling involved in the reported case; done means supports remain at the actual collision points with negative scale while the existing positive-scale behavior still works.
Written by the indexing model from the issue text.
Assessment
- Tech stack
- javascript
- Domain
- game-dev
- Issue type
- Bug
- Difficulty
- 4/5
- Estimated time
- 3-5 days
- Activity status
- Quiet
- Clarity
- Mostly clear
- Newbie friendliness
- 35/100