Outputs a default header into the RIB stream. This function can be called right after RiBegin() to write the following information into the RIB stream:
##RenderMan RIB-Structure 1.1 ##Creator <Filename> ##CreationDate <Date> ##For <User>
The "For" information is left out if the user name cannot be determined.
Outputs a grid primitive. thickness determines the thickness of the grid lines and cells the number of gridlines. The grid lies on the XY plane and is centered at the origin. The grid spacing is 1 unit. The grid uses the given shader and color.