primduv expression function
Returns the partial derivatives of a primitive attribute.
Replaced by: hou.CurvedSurface
See also: primuv, normal, curvature, unituv
Usage
primduv(surface_node, prim_num, attrib_name, attrib_index, u, v, du, dv)
Evaluates the (partial) derivatives of a face or hull attribute at a parametric (u,v) position. u and v are unit values, defined in the [0,1] interval. When given the “P” or “Pw” attribute, the positional derivative of (u,v)'s image on the primitive will be returned. If the primitive is a face type, v and dv are ignored. If both du and dv are 0, primduv becomes equivalent to primuv.
if the primitive is a polygon or a mesh, u and v are defined in terms of the number of vertices, or rows or columns respectively.
Examples
primduv("/obj/geo1/tube1", 12, "P", 2, 0.4, 0.5, 1, 0)
Evaluates the Z component of the first-order partial derivative of primitive 12 with respect to u, at the parametric location (0.4,0.5).