Hello,
Does anyone know if vector displacement maps are supported in materialx/karma? It appears to be according to the documentation. It says:

"(Float or Vector3) If Float, scalar displacement amount along the surface normal direction. If vector3, Vector displacement in (dPdu, dPdv, N) tangent/normal space."

I have no trouble with regular displacement maps. I am trying to use the vector displacement maps that you export from the ocean evaluate sop. (the reason I am doing this instead of the karma ocean lop is because that doesn't work with xpu).

The first image is the just a render with no displacement. It is the output of the ocean spectrum. So this the "ground truth". When I add displacement to a flat grid it should match this.

The second image is if I use my vector displacement map. See how it is flat and definitely not correct. If I scale the displacement it looks strange.

I read somewhere that vector displacement maps can be read xyz or xzy. So the third/fourth image is if I swap the y and z components of the vector. The result is almost perfect. You probably can't tell unless you are toggling back and forth, but the displacement heightwise (in y) is prefect. But its a bit off in the x and z slightly.

I should mention this works in mantra with the principled shader. If I set the displacement texture to vector and space to world or object space (not tangent).

Any tips/suggestions?

try: +x -z +y
I mean just guessing, but since it looks like that mtlx displacement expects tangent space vector and I assume your UVs are aligned along +x and -z, and N points in +y, it could in theory work

tamte
try: +x -z +y
I mean just guessing, but since it looks like that mtlx displacement expects tangent space vector and I assume your UVs are aligned along +x and -z, and N points in +y, it could in theory work

Oh, if it expects tangent space for vector displacement, then it probably won't work 100% because I believe the ocean spectrums output is either object space or world space. If I use mantra to render this grid and set to use vector displace and use object space it works. But it doesn't work in tangent space.

As I mentioned since your grid and UVs are aligned with world space you should be able to find matching tangent space just by shuffling the axes

Did you try what I mentioned?
If it didn't work it may be different axes/directions but should be easy to find match

<h1>Hello</h1> I am new to all of this. How does it work?

tamte
As I mentioned since your grid and UVs are aligned with world space you should be able to find matching tangent space just by shuffling the axes

Did you try what I mentioned?
If it didn't work it may be different axes/directions but should be easy to find match

It was more off than my default settings of xzy. Everything I do is close, but nothing is perfect. It should be good enough,however.