getuvtangents

Context(s)	displace fog light shadow surface

void  getuvtangents(string objName, vector P, vector dir, vector &Tu, vector &Tv)

This variant additionally sets Tn to the evaluation point’s surface normal:

void  getuvtangents(string objName, vector P, vector dir, vector &Tu, vector &Tv, vector &Tn)

Note The object must have a vector attribute named “uv”.

Tip Passing “” as the objName parameter will cause the function to use the current shaded object.

objName

Name of object to evaluate UV tangents for.

P

Point at which to evaluate UV tangents.

dir

The direction to use for searching the object’s surface.

The surface of the object is searched for by casting rays from P in this direction as well as the opposite direction.

When available, it makes sense to use the normal at the point being evaluated.

Tu

UV tangent in U direction.

Tv

UV tangent in V direction.

Tn

The surface normal at the point where tangents are evaluated.

// Get UV tangent at 'P', searching the surface in the direction of 'N'
vector Tu, Tv;
getuvtangents("/obj/geo1", P, N, Tu, Tv);

// Find a surface location using an arbitrary ray.
// In this case the surface normal isn't known beforehand and can be fetched via 'Tn'.
vector Tu, Tv, Tn;
getuvtangents("/obj/geo1", ray_orig, ray_dir, Tu, Tv, Tn);