The RenderMan Interface - Paul Bourke

parameterlist is a list of token-array pairs where each token is one of the standard
geometric primitive variables, a variable that has been defined with RiDeclare, or is
given as an inline declaration. The parameter list must include at least position (”P”)
information. If a primitive variable is vertex or varying, the array contains n elements
of the type corresponding to the token, where n is equal to the maximum value in
the array vertices plus one. Primitive variables that are vertex will be interpolated
according to the subdivision rules (just as ”P” is), whereas varying data will be interpolated
linearly across faces (as is done for a PointsPolygons). If the variable is
uniform, the array contains nfaces elements of the associated type. If the variable is
constant, a single element of the associated type should be provided.
A component is either a face, a vertex, or a chain of edges. Components of the subdivision
mesh may be tagged by the user to have various implementation-specific
properties. The token array tags, of length ntags, identifies these tags. Each tag has
zero or more integer arguments, and zero or more floating-point arguments. The
number of arguments provided with each tag is specified by the array nargs, which
has a length of ntags × 2. For each tag, nargs contains an integer specifying the number
of integer operands found in the array intargs, followed by an integer specifying
the number of floating-point operands found in the array floatargs. Thus, the length
of intargs is equal to the sum of all the even-numbered elements of the array nargs.
The length of floatargs is equal to the sum of all the odd-numbered elements of the
array nargs.
The standard tags are ”hole”, ”crease”, ”corner”, and ”interpolateboundary”.
The ”hole” tag specifies that certain faces are holes. This tag has n integer arguments,
one for each face that is a hole, and zero floating-point arguments. Each face is specified
by its index in the nvertices array.
The ”crease” tag specifies that a certain chain of edges should be a sharp crease. This
tag has n integer arguments specifying a chain of vertices that make up the crease,
and one floating-point argument that is expected to be RI INFINITY. Each sequential
pair of vertices in a crease must be the endpoints of an edge of the subdivision mesh.
A mesh may have any number of independent ”crease” tags. Individual renderer implementations
may choose to expand the functionality of the ”crease” tag by making
use of tag values other than RI INFINITY.
The ”corner” tag may be used to mark certain vertices as sharp corners. This tag
has n integer arguments containing the vertex numbers of the corners and either
one or n floating-point arguments that are expected to be RI INFINITY. Individual
renderer implementations may choose to expand the functionality of the ”crease” tag
by making use of tag values other than RI INFINITY.
The ”interpolateboundary” tag specifies that the subdivision mesh should interpolate
all boundary faces to their edges. This tag has zero integer arguments and zero
floating-point arguments. It has the same effect as specifying that all the boundary
edge-chains are sharp creases and that boundary vertices with exactly two incident
edges are sharp corners.
RIB BINDING
SubdivisionMesh scheme nvertices vertices tags nargs intargs floatargs ...parameterlist...
The number of faces is determined implicitly by the length of the nvertices array.
76