TYPE: SOP
TITLE: Vertex SOP

The Vertex operation manipulates the color and texture coordinates using vertex
rather than point attributes. It supports two inputs, and will inherit the first
input source by default. Any existing point attributes will be elevated to
per-vertex attributes.

Examples:
    vertex/cr = $BBX 	   - Set the red colour to the bounding box
                             relative X position of the vertex.
    vertex/cg = $CG2 	   - Set the green to the green of the second
			     input's vertex.
    vertex/cb = $CB - $CB2 - Set the blue value to the difference
			     between the first inputs blue and the
			     second inputs blue.

Parameters:
    Group             - Subset of primitives whose vertices are to be affected.
    Color             - Diffuse color (RGB)           /diffr /diffg /diffb
    Alpha             - Transparency value                          /alpha
    Texture           - Texture coordinates           /mapu  /mapv  /mapw
    Crease            - Crease weight for polygonal subdivision     /crease
                        Use the Primitive operation to create a crease of
                        constant weight for the entire primitive.

Local Variables
    PT, NPT           - Point number and total number of points.
    PR, NPR           - Primitive number & total number of primitives.
    VTX, NVTX         - Vertex number & total number of vertices.
    CEX, CEY, CEZ     - Centroid of the geometry.
    BBX, BBY, BBZ     - Relative position of point within bounding box.
                        Values are mapped between 0 and 1.
    TX, TY, TZ        - Point position.
    NX, NY, NZ        - Point normal directions.
    MAPU, MAPV, MAPW  - Point or vertex texture coordinates.
    CR, CG, CB        - Diffuse point or vertex color.
    CA                - Point or vertex alpha value.
    CREASE            - Point or vertex crease weight value.
    PT2, NPT2, etc    - Append 2 for the second source.

See also: Point, Primitive
