The RenderMan Interface - Paul Bourke

RtFloat knot[12] = { 0,0,0,1,1,2,2,3,3,4,4,4 };
RtFloat min[1] = { 0 };
RtFloat max[1] = { 4 };
RtInt n[1] = { 9 };
RtFloat u[9] = { 1.0, 1.0, 1.0, 0.0, 0.0, 0.0, 1.0, 1.0, 1.0 };
RtFloat v[9] = { 0.5, 1.0, 2.0, 1.0, 0.5, 0.0, 0.0, 0.0, 0.5 };
RtFloat w[9] = { 1.0, 1.0, 2.0, 1.0, 1.0, 1.0, 2.0, 1.0, 1.0 };
RiTrimCurve (nloops, ncurves, order, knot, min, max, n, u, v, w);
SEE ALSO
RiNuPatch, RiSolidBegin
5.3 Subdivision Surfaces
The RenderMan Interface includes support for subdivision surfaces. Ordinary cubic B-
spline surfaces are rectangular grids of tensor-product patches. Subdivision surfaces generalize
these to control grids with arbitrary connectivity. The API for subdivision surfaces
looks a lot like RiPointsPolygons, with additional parameters to permit the specification
of scheme-specific and implementation-specific enhancements.
A subdivision surface, like a parametric surface, is described by its control mesh of points.
The surface itself can approximate or interpolate this control mesh while being piecewise
smooth. Furthermore, its control mesh is not confined to be rectangular, which is a major
limitation of NURBs and uniform B-splines. In this respect, the control mesh is analogous
to a polygonal description. But where polygonal surfaces require large numbers of
data points to approximate being smooth, a subdivision surface is smooth — meaning that
polygonal artifacts are never present, no matter how the surface animates or how closely it
is viewed.
RiSubdivisionMesh ( RtToken scheme, RtInt nfaces, RtInt nvertices[], RtInt vertices[],
RtInt ntags, RtToken tags[], RtInt nargs[],
RtInt intargs[], RtFloat floatargs[], ...parameterlist...)
RiSubdivisionMesh defines a subdivision mesh or surface obeying the subdivision
scheme specified by scheme. The only standard scheme is ”catmull-clark”, specifying
the Catmull-Clark subdivision method. Implementations may also support other
schemes. The subdivision mesh is made up of nfaces faces. The array nvertices,
of length nfaces, contains the number of vertices in each face. The array vertices
contains, for each face vertex, an index into the vertex primitive variable arrays. The
array vertices has a length equal to the sum of all the values in the array nvertices.
All the arrays are 0-based.
75