Sample NURBS Surface normal at uv?

[Juraj]

Hello,
is there a VEX function for sampling N at arbitrary location in NURBS surface (based on uv location for example)?
One way would be to convert NURBS to polys and get normals from them. But I thought that maybe there is easy way of getting N directly from NURBS?

 

Thanks,
Juraj

[iamyog]

primuv() should do: http://www.sidefx.com/docs/houdini/vex/functions/primuv

[Juraj]

Thanks, it works, I can get P and N attributes (even if there is no N attribute at NURBS surface)
Is there a list of attributes I can import from NURBS surface? maybe tangent, bitangent?

However I am not sure if it is a bug or something, but it is super slow to sample those attributes. It takes 2 seconds to compute very simple wrangle on quite fast pc

int prim;
vector uv;
float dist = xyzdist(1, v@P, prim, uv);

vector N = primuv(2, "N", prim, uv);

if (dist < chf("tr")) {
    v@P = primuv(2, "P", prim, uv) + N*dist;
}

If I use the same wrangle but with NURBS converted to polys, then I have realtime feedback when modifying NURBS surface.

Edited January 16, 2017 by Juraj
typo