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Cycles bake - high-> lowpoly bake triangle orientation is mixed for texture coords in shader normals.
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Description

System Information
win 8.1 32gb
nvidia 880m 8gb

Blender Version
Broken: 2b5e150
Worked: probably never

Short description of error
generated noise texture is wrongly mapped in other direction, when baking selection to active in the provided file. The artifacts are quite gentle, and only happen to normals of the shader(not baked normals). Also, if the texture is mapped to color of shader, the color is ok.
the bug doesn't happen when triangulate modifier is added to the target object.
This happens for me on many objects, this is just one example.

Exact steps for others to reproduce the error
open the file, hit bake.
add triangulate to the "test" object, voila, problem gone.


Details

Type
Bug

Event Timeline

Vilem Duha (pildanovak) updated the task description. (Show Details)
Vilem Duha (pildanovak) raised the priority of this task from to Needs Triage.
Vilem Duha (pildanovak) set Type to Bug.
Bastien Montagne (mont29) triaged this task as Normal priority.Jul 17 2015, 7:34 PM

Dalai, maybe you can check this one? Thanks.

Just a comment - it looks very similar to other artifacts you can get in other bugs, but it's not a duplicate. All somehow manage to mix something up, but they are all different by the specific conditions in which they happen.

Upadte - this also happens with highpoly objects, so even if the lowpoly object has triangulate, it can still happen.
When both objects have triangulate, then it's ok.

just uploaded a file for the above comment - you can see half a triangle has an artifact, it's probably because of the triangulation of both objects acting over each other. Here the artifact is again quite subtle, but I guess it's visible how the coords are rotated. again, add triangulate to the object which gets baked from to fix the artifact and see the difference


I'm not sure I can see the artifact here. Also it's a strange report because 'internally' we add a triangulate modifier to the highpoly object, exactly to prevent triangulation issues.

I simplified the file a bit, and I can confirm that there is some difference when triangulating (or not) the low poly object. File:

  • Original:
  • Triangulated:

@Brecht Van Lommel (brecht) do you think this can be caused by the differentials calculation?
The differential calculation that we do is based on the image space and the low poly object uv.

The differentials are relative to the UV/image space, so the highpoly differentials
are the same as the low poly differentials

Since the issue shows up when using bump map, and is sensitive to the low poly object geometry, I believe it's related to the differentials.

I can confirm this bug in 2.75 and 2.76, but in latest master this seems to be all fine. There were various fixes regarding triangulation consistency, which I suspect fixed this, but did not try to find the specific commit that did it.