The RenderMan Interface - Paul Bourke

onto a surface. Texture maps are used in many different ways: direct image mapping
to change the surface’s color, transparency mapping, bump mapping for changing
its normal vector, displacement mapping for modifying position, environment or reflection
mapping for efficiently calculating global illumination, and shadow maps for
simulating the presence of shadows.
The RenderMan Interface is designed so that the information needed to specify a photorealistic
image can be passed to different rendering programs compactly and efficiently. The
interface itself is designed to drive different hardware devices, software implementations
and rendering algorithms. Many types of rendering systems are accommodated by this interface,
including z-buffer-based, scanline-based, ray tracing, terrain rendering, molecule
or sphere rendering and the Reyes rendering architecture. In order to achieve this, the
interface does not specify how a picture is rendered, but instead specifies what picture is
desired. The interface is designed to be used by both batch-oriented and real-time interactive
rendering systems. Real-time rendering is accommodated by ensuring that all the
information needed to draw a particular geometric primitive is available when the primitive
is defined. Both batch and real-time rendering is accommodated by making limited
use of inquiry functions and call-backs.
The RenderMan Interface is meant to be complete, but minimal, in its transfer of scene
descriptions from modeling programs to rendering programs. The interface usually provides
only a single way to communicate a parameter; it is expected that the modeling front
end will provide other convenient variations. An example is color coordinate systems –
the RenderMan Interface supports multiple-component color models because a rendering
program intrinsically computes with an n-component color model. However, the Render-
Man Interface does not support all color coordinate systems because there are so many and
because they must normally be immediately converted to the color representation used by
the rendering program. Another example is geometric primitives – the primitives defined
by the RenderMan Interface are considered to be rendering primitives, not modeling primitives.
The primitives were chosen either because special graphics algorithms or hardware
is available to draw those primitives, or because they allow for a compact representation
of a large database. The task of converting higher-level modeling primitives to rendering
primitives must be done by the modeling program.
The RenderMan Interface is not designed to be a complete three-dimensional interactive
programming environment. Such an environment would include many capabilities not
addressed in this interface. These include: 1) screen space or two-dimensional primitives
such as annotation text, markers, and 2-D lines and curves, and 2) user-interface issues
such as window systems, input devices, events, selecting, highlighting, and incremental
redisplay.
The RenderMan Interface is a collection of procedures to transfer the description of a scene
to the rendering program. These procedures are described in Part I. A rendering program
takes this input and produces an image. This image can be immediately displayed on a
given display device or saved in an image file. The output image may contain color as well
as coverage and depth information for postprocessing. Image files are also used to input
texture maps. This document does not specify a ”standard format” for image files.
The RenderMan Shading Language is a programming language for extending the predefined
functionality of the RenderMan Interface. New materials and light sources can be
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