Wrong vertex normals and uvs after boolean subtraction about manifold

[jirihon]

I've just noticed you merged the new triangulator. The described example works with the new triangulator. But it was quite easy to find another example of wrong normals and uvs, so I think the triangulator won't be the problem here. I'll try to prepare another example which shows the problem for the current master.

[jirihon]

Here is a new mesh dump which shows the same problem for the current master.

wrong_normals_and_uvs_mesh_dump_2.txt

The problematic triangles here are 17 and 28 which use vertex 8 with inappropriate normal and uv.

[pca006132]

are there degenerate triangles in the result? or duplicated vertices at the same position?

[jirihon]

are there degenerate triangles in the result? or duplicated vertices at the same position?

How do I check this? I'm using WASM bindings. I have duplicated vertices because I need different normals and uvs for different surfaces, but I set mergeFromVert and mergeToVert, so it is manifold.

[pca006132]

I think we don't have that API in our js binding because it is only intended for debugging.

For this bug, I feel like it may be related to degenerate triangles or vertices with same position because the normal computation for them are probably not very stable. Can you try if it works if you modify https://github.com/elalish/manifold/blob/master/src/manifold/src/impl.cpp#L70 a bit to ignore edges with length less than precision?

[elalish]

Thank you for the detailed report - this definitely sounds like a bug. The next step will be turning it into a reproducible TEST; hopefully our RelatedGL testing function can help here.

[jirihon]

I think we don't have that API in our js binding because it is only intended for debugging.

For this bug, I feel like it may be related to degenerate triangles or vertices with same position because the normal computation for them are probably not very stable. Can you try if it works if you modify https://github.com/elalish/manifold/blob/master/src/manifold/src/impl.cpp#L70 a bit to ignore edges with length less than precision?

I've checked the triangle areas by using cross product of the AB and AC vectors. The smallest triangle I could find in a, b and a_minus_b manifolds has area of 1560.33, so I don't think any of the triangles is degenerate.