As far as I remember, Renderman's geometry primitive at the time of Toy Story 1 was called a "grid" and it was some sort of quadratic B-spline patch. Even polygons were converted to grids for shading and rendering IIRC, and of course NURBS surfaces were diced to grids as well.
Most of the geometry pipeline was basically a "divide and conquer" loop, where all the geometry primitives were split and re-processed again until their size went under a predefined threshold.
This had a few consequences for the rendering:
- displacement mapping was almost free because everything was tessellated to subpixel size anyway
- shading was only calculated for the grid points and interpolated from there (so it was sort of a vertex shading approach
)
- shader antialiasing was linked to the level of tessellation (it was called "shading rate")
Rendering was also done by "buckets" or what we call tiles in realtime rendering. This was to keep memory use manageable, as only the grids contained in the bucket had to be kept in RAM.
The above is also why there's no point in making any comparisons using the original assets. Except for PRMan, no current renderer would be able to process them the same way. You can of course do any kinds of custom tessellations, and render them as triangles, but it wouldn't be a close enough match; and tessellating to the levels that was used in the movie is useless anyway, as all renderers do shading in different ways.
However, Pixar has implemented Catmull-Clark subdivision surfaces by the time they started on Toy Story 2 (after all Ed Catmull was and is their CTO...), and thus they converted all the NURBS assets to subdivs for TS2. The control cage of a subdiv model is not really different from a polygon mesh, and every software renderer today has support for subdivs; even many realtime engines should be able to support them.
PRMan still tessellated subdivs to grids (and does so today as far as I know) so what it actually renders was just as different, but at least it would be a closer comparison.