This is RenderMan 21 Documentation you are viewing. The Rmanwiki home page will redirect you to the current documentation.
Primitive variables (often referred as "primvar") are data attached to the geometry. This is useful when a shader needs to reference custom data from the geometry such as foam in an ocean shader.
Mapping Houdini to RenderMan Primvar
When the primitive variable is already available in Houdini such as from an alembic file, we can add Attribute Rename to map it to RenderMan primvar.
We then specify the variable name mappng from the Houdini to RiName (the primvar name) as well as its RiType (the primvar type).
Inside the RIS Network, we create a PxrPrimvar to read this primvar.
For example, we wire the resultF of PxrPrimvar to a PxrSurface's Diffuse Gain.