SDK: Tangent and Bitangent

V-Ray V-Ray Common Public
1

Hi,

is there any pre-computed Tangent and Bitangent available somewhere, or do I have to compute it myself?

And if I have to compute it myself.. how would I do this? Because I can’t find any information about the triangle-UVs that I’d need in the VRayContext :frowning:

Aya~

2

You can get this information by querying the sd (ShadeData) of VRayContext::rayresult for the MappedSurface interface. Then use it to retrieve the transformation from world to texture space. Then invert this transformation and use its x and y columns to get the world space coordinates of the tangent and bi-tangent vectors.

Something like this:

MappedSurface *mappedSurf=(MappedSurface*) GET_INTERFACE(rc.rayresult.sd, EXT_MAPPED_SURFACE);
if (mappedSurf) {
    Matrix worldToTex=mappedSurf->getLocalUVWTransform(rc, channel).m;
    Matrix texToWorld=inverse(worldToTex);
    texToWorld.f[0]; // this is the tangent
    texToWolrd.f[1]; // this is the bi-tangent
}

Hope this helps.

Greetings,
Vladimir Nedev

3

This is correct for Maya, but for 3ds Max you can simply use the ShadeContext:: DPDUVW() method. Note however that the result from this is not continuous across triangles. If you need the continious vectors, let me know.

Best regards,
Vlado