RenderMan Interface Specification

File:Pixar Renderman.png

RenderMan is an API developed by Pixar Animation Studios to describe three dimensional scenes and turning them into digital photorealistic images. The full name is the RenderMan Interface Specification.

RenderMan also is the part of the name of a rendering software package developed by Pixar^[1] which implements this API.

RenderMan is often used in creating digital visual effects for the Hollywood blockbuster movies of today such as Star Wars and The Lord of the Rings.

Terminology

The name RenderMan can cause confusion because it is often used to refer to different things:

• The RenderMan Interface Specification (RISpec) ^[2], including the RenderMan Shading Language: Pixar's technical specification for a standard communications protocol (or interface) between modeling programs and rendering programs capable of producing photorealistic-quality images. This is a similar concept to PostScript but for describing 3D scenes rather than 2D page layouts. Thus, modelling programs which understand the RenderMan Interface protocol can send data to rendering software which implements the RenderMan Interface, without caring what rendering algorithms are utilized by the latter. The interface was first published in 1988 and was designed to be sufficiently future proof to encompass advances in technology for a significant number of years.
• PhotoRealistic RenderMan (PRMan) sold as part of a bundle called RenderMan Pro Server: A RenderMan-compliant rendering software system developed by Pixar based on their own interface specification. PRMan is chiefly a Reyes algorithm implementation, although recent versions also include ray tracing and global illumination features. PRMan is used internally at Pixar and also licensed to third parties.
• RenderMan for Maya: A scaled down version of PRMan that is designed to be completely integrated with the Maya 3D content development package.

RenderMan Interface Specification

What set the RISpec apart from other standards of the time was the specification of a shading language (SL), which allowed material descriptions of surfaces to be described not only by adjusting a small set of parameters, but in an arbitrarily complex fashion by using a C-like programming language to write shading procedures commonly known as procedural textures and shaders. Lighting, and displacments on the surface are also programmable using the SL language. The shading language allows, though does not insist, that each statement can be executed in a SIMD manner. Another thing that sets the renderers based on the RISpec apart from many other renderers, is the ability to output arbitrary variables as an image—surface normals, separate lighting passes and pretty much anything else can be output from the renderer in one pass.

RenderMan has much in common with OpenGL, despite the two APIs being targeted to different sets of users (OpenGL to real-time hardware-assisted rendering and RenderMan to photorealistic off-line rendering). Both APIs take the form of a stack-based state machine with (conceptually) immediate rendering of geometric primitives. It is possible to implement either API in terms of the other.

Further reading

• Steve Upstill: The RenderMan Companion: A Programmer's Guide to Realistic Computer Graphics, Addison-Wesley, ISBN 0-201-50868-0
• Anthony A. Apodaca, Larry Gritz: Advanced RenderMan: Creating CGI for Motion Pictures, Morgan Kaufmann Publishers, ISBN 1-55860-618-1
• Ian Stephenson: Essential RenderMan Fast, Springer, ISBN 1-85233-608-0
• Saty Raghavachary: Rendering for Beginners: Image synthesis using RenderMan, Focal Press, ISBN 0-240-51935-3
• David S. Elbert, et al: Texturing and modeling: a procedural approach, AP Professional, ISBN 0-12-228730-4

1. ^ Robert L. Cook., Loren Carpenter, and Edwin Catmull. "The Reyes image rendering architecture." Computer Graphics (SIGGRAPH '87 Proceedings), pp. 95–102.
2. ^ "RenderMan - Developers Corner - RI Specs". 2005-12-18.

External links

• RenderMan® Repository
• Renderman Learning Resource
• RenderMan compliant Renderers:
  • Digits 'n Art's 3Delight
  • Sitexgraphics' AIR (Advanced Image Rendering)
  • Aqsis (open source)
  • jrMan (open source, Java-based)
  • Pixar's PhotoRealistic RenderMan
  • Pixie (open source)
  • DotC Software's RenderDotC
• RenderMan tools:
  • AnimalLogic Mayaman (connects several of the above renderers to Maya)
  • Archonus' PaxRendus (Connects several of the above renderers to 3D Studio Max)
  • Liquid (open source, connects several of the above renderers to Maya)
  • ShaderMan (A free shader building tool)
  • Tim Dapper's LightMan
• RenderMan knowledge:
  • Death Fall
  • Zhang Jian
  • CG References & Tutorials by Prof. Malcolm Kesson
  • RenderMan Notes (notes on shader writing)