Why zero height mesh gets black independent of shader

Question

When altering the scale of a gameobject with a mesh built procedurally, I've realized it gets all blacked out in Unity5, instead of dark gray in previous versions.

Testing with the default 3D cube from "GameObject -> 3D object -> Cube" the same thing happenned, so I'm confident there's nothing particularly wrong with the mesh generation.

After a couple of trial and error experiments, 1e-12 is the smallest height for which material and color properties seem to take effect in Unity5. In Unity 4.6.1f1 it rendered the expected color with height as low as 1e-19.

Anyone knows why you can't have a zero height render itself correctly and how to do it if there's a way? The project where it's being used doesn't need them to be actually zero height, but the work around for this small problem is quite a lot of work.

Thanks in advance

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Answer by Piflik · Jul 16, 2015 at 11:43 AM

Unity automatically flips face normals according to the sign of the numbers in the scale-vector, to prevent negatively scaled objects from turning inside out. At 0 scale, this breaks.

The cutoff at 1e-12 doesn't really make any difference compared to 1e-19, neither visaully nor mathematically. There is not much that you cannot do with 12 orders of magnitude that would be possible with 19. Especially if you factor in float-inaccuracies.

If you need flat geometry, use flat geometry, like Planes (NOT aircrafts) or Quads.

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Radetic · Jul 17, 2015 at 11:40 AM 0

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The cutoff was really just a curiosity. For another part of this program we really use quads just to avoid all this pain of loosing material properties. However, a few features demand extrudable regular polygons and the work around was set the scale to keep a minimum height of 1e-12.

Thanks for the attention and the insight on normals.

Why zero height mesh gets black independent of shader

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