The RenderMan Interface - Paul Bourke

and uniform variables on an RiNuPatch has now officially been deemed to be computed as
if the NuPatch is a nonperiodic uniform B-spline mesh, rather than a single B-spline patch.
Details are given in Section 5.2 where the RiNuPatch primitive is described.
The 3.1 spec implied that Shading Language variable initialization expressions could only
be uniform. That restriction is lifted.
The Shading Language variables du and dv are potentially varying, and are not restricted
to be uniform as the 3.1 specification suggests.
A number of new optional arguments to the Shading Language texturing functions have
been added: ”blur”, ”sblur”, ”tblur”, ”filter”, ”fill”.
Many new built-in functions, or new variants of existing functions, have been added to
the Shading Language, including: inversesqrt, random, transform, vtransform, ntransform,
determinant, concat, format, match, translate, rotate, scale, ctransform, ptlined, filterstep,
noise, cellnoise, pnoise, specularbrdf, attribute, option, textureinfo, rendererinfo, min, max,
clamp, mix, spline, atmosphere, displacement, lightsource, surface, Dtime.
The illuminance statement has been expanded to accept category specifiers.
Shading Language has added new variables: dtime and dPdtime.
Rather than strictly requiring user-defined and nonstandard data to be typed using RiDeclare,
such tokens can have their types specified “in-line” by prepending the type declaration
to the token name.
Renderers may output images composed of arbitrary data computed by shaders, in addition
to “rgb” and so on. Such extra data may also be sent to different output files.
We have clarified that interior and exterior volume shaders are not specific to CSG solids,
but rather are shaders that alter the colors of rays spawned by trace() calls in the shaders
of the primitive.
RiArchiveRecord now takes ”verbatim” as the record type.
We have clarified that in imager shaders, P is the raster space position of the pixel center,
and not the point on any piece of scene geometry.
We have changed the wording of the section that once described the required versus optional
capabilities of RenderMan-compliant renderers. A few features previously described
as optional, such as programmable shading, texture mapping, and trim curves, have been
moved unambiguously to the list of requirements. There is still a list of “advanced features”
that are no longer referred to as “optional,” but it is understood that algorithmic
limitations may prevent some implementations from fully supporting those features.
Object Instances are a bit more flexible in 3.2 than they were in 3.1. In particular, relative
transformations and Motion blocks are allowed within Object definitions.
Some changes have been made to the required standard shaders: they have been updated
to make use of the new data types, the bumpy shader now does displacement instead of
using the depricated bump() function, and there is now a standard background imager
shader.
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