ConvexPolyhedron with imported geometry can't collide against each other ?

[Faber-smythe]

Hi there !
First I'm a newbie so tell me right away if I'm asking in the wrong place or didn't get something basic.

I'm importing basic meshes from Blender and throwing them on a plane. But it crashes as soon as they collide against each other. I don't get why.
Here is a straight forward sandbox to reproduce my case. Has anybody a clue as to what could be the problem ?

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It might not be related, but it was pointed to me that in cannon.js ConvexPolyhedron class doesn't accept coplanar triangles :
"No polygons may be coplanar (contained in the same 3D plane), instead these should be merged into one polygon."

It seems really strange, since three.js geometries only work with triangular faces (quads are cut in half). This is also how GLTF export works. In Blender I had a plain cube, with 6 faces, but the exported model has 12 faces.

Also if instead of my imported geometry I pick the native BoxGeometry (which works just fine and collides without crashing), and log it, I'll find that it has indeed 12 faces.

I have no idea what to do with that. It sounds very very strange that cannon.js convex polyhedron can't have coplanar polygons, while three.js specifically work that way.

[Faber-smythe]

So…
THE CAUSE :
In the process of cuting quads into triangles, Blender GLTF export multiplies the vertices. This doesn’t bother the rendering of the meshes in Three.js, but causes crashing deep into cannon-es script when two of them collide with each other.

THE FIX :
The geometry can be cleaned up with geometry.mergeVertices(). This caused the duplicated vertices to disappear, and the geometry.faces to be remapped onto the new geometry.vertices.

The CodeSandBox here shows the issue and the fix.

[stockhuman]

Well done on troubleshooting this on your own! For the next person that comes around, note that some stuff like this is mentioned within the demos, where you might find other useful "recipes". :)