unituv expression function
Converts real UV to unit UV.
See also: realuv
unituv(surface_node, prim_num, uv_real, D_U|D_V)
The unit value is defined in the [0,1] interval. The real value is defined in the valid interval of the primitive’s domain if the primitive is a spline type. If the primitive is a polygon or a mesh, the size of its domain is given by the number of vertices, or rows or columns respectively. If the primitive is a polygon or a curve, D_U and D_V are irrelevant.
the result is undefined if the primitive is neither a face nor a hull.