There is indeed a bug in Octane which causes it to use a wrong “tangent vector” when the UV map is mirrored. This vector determines the orientation of the normal map distortion (more specifically: the color (1.0, 0.5, 0.5) specifies a distortion in the direction of this vector).
We will fix that bug, but this however will not fix the problem with this render. At the moment Octane assumes that the UV mapping is not mirrored, and it will also not mirror any distortions in the normal map. So you still end up with a normal which is mirrored around the U axis in 2 of the 4 quadrants:
Let's for example use a simple normal map:
- Normal map example
- border-tiny-corner.png (1.99 KiB) Viewed 5577 times
And render it on a square with mirrored UV coordinates in the 4 quadrants:
Note that although you only see one seam, the normal map is wrong in the upper right and lower left quadrant. Note the orientation of the highlights on the mirrored
n.
Using just the usual UV mapping on a plane and relying on our mirror border mode for textures doesn't result in edges, but it still results in wrong orientations because the normal map distortion still needs to be mirrored in the right and bottom parts of the quad (note the bottom border).
We are at the moment not planning to implement this kind of mirroring in Octane. The only way right now is to convert this normal map into a bigger normal map covering all 4 quadrants (and applying the right mirroring). Is this a common use case?
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Roeland