RenderMan is Pixar’s rendering system: the software that turns three-dimensional scene descriptions into finished images, together with a published standard, the RenderMan Interface Specification, that defines how those scenes are described. Pixar’s RenderMan tech-specs page dates the standard to 1988, when “RenderMan established an open standard to describe 3D data: the RenderMan Interface Specification (the RISpec).” The idea was to separate the description of a scene from the program that renders it, so that modeling tools and renderers from different vendors could interoperate.
The RenderMan Interface Specification is a substantial technical document. Version 3.2, published by Pixar in July 2000, runs to fifteen chapters and a set of appendices covering the geometric primitives, transformations, cameras, lights, and especially the shading model that a compliant renderer must support. A key part of the standard is the RenderMan Shading Language, which lets artists and technical directors write programmable shaders that compute surface color, displacement, light, and volume effects, rather than relying on a fixed set of built-in materials.
In its early years RenderMan was built on the Reyes architecture (Renders Everything You Ever Saw), a micropolygon-based rendering pipeline developed by Pixar’s research group. As Pixar’s own evolution-of-RenderMan page explains, the Reyes algorithm “allowed RenderMan to render photorealistic images by faking these effects … without raytracing,” which was essential given the limited computing power of the 1980s. This made it possible to render scenes of enormous complexity within the hardware budgets of the era.
The scene data itself is typically expressed in the RenderMan Interface Bytestream, or RIB, a text or binary format that records the same calls defined by the C-language RenderMan Interface. Because the interface was published as an open specification, third-party renderers such as Blue Moon Rendering Tools (BMRT) were written to implement the standard, and many modeling and animation packages learned to export RIB.
Over the decades RenderMan moved well beyond its Reyes roots. Pixar’s evolution page describes a progression from REYES to a hybrid renderer, then to the RIS path-tracing system, and most recently to the XPU architecture that uses both CPU and GPU. Modern RenderMan is a physically based, ray-tracing and path-tracing renderer that supports global illumination directly, a sharp contrast to the early micropolygon approach that deliberately avoided ray tracing.
RenderMan’s significance lies both in the software and in the standard. As a tool it rendered Toy Story (1995) and a long line of feature films and visual-effects shots; as a specification it gave the industry a shared, programmable vocabulary for describing and shading three-dimensional scenes, influencing rendering systems far beyond Pixar.