SDK: Tangent and bitangent

[eliang]

Hi,

I need to function to transform vectors between world and tangent space.
I found this:

http://www.chaosgroup.com/forums/vbu...ight=bitangent

From the sample code, I wrote this function:

Matrix worldToTangent(const VRayContext& rc)
{
    MappedSurface* mappedSurf = (MappedSurface*) GET_INTERFACE(rc.rayresult.sd, EXT_MAPPED_SURFACE);
    return mappedSurf->getLocalUVWTransform(rc, 0).m;
}

Is the matrix I get from this function a pure rotation matrix?
I ask because it transforms my unit vectors into non-unit which doesn't seem right.

Thanks!

[vlado]

No, it is not a pure rotation matrix; it is used to transform an offset relative to the shaded point from world space to texture space. To get the tangent and bitangent vectors, you will need to invert the matrix and get its first two columns.

Best regards,
Vlado