The RenderMan Interface - Paul Bourke

color c, d=1, e=color(1,0,0);
The initialization value may be any scalar or color expression. If a scalar expression is used,
its value is promoted to a color by duplicating its value into each component.
Colors may be specified in a particular color space by:
color [space] (u,v,w)
The optional specifier space, which must be a string literal, indicates the color coordinate
system of the 3-tuple. The default color coordinate system is ”rgb”. This construct lets you
specify the color u,v,w in a particular color space, but this statement implicitly converts
the color into its ”rgb” equivalent. Table 11.1, Color Coordinate Systems, lists the color
coordinate systems that are supported in the Shading Language.
Coordinate System
”rgb”
”hsv”
”hsl”
”xyz”, ”XYZ”
”YIQ”
Description
Red, green, and blue.
Hue, saturation, and value.
Hue, saturation, and lightness.
CIE XYZ coordinates.
NTSC coordinates.
Table 11.1: Color Coordinate Systems.
11.3 Points, Vectors, and Normals
Point-like variables are (x,y,z) triples of floats that are used to store locations, direction vectors,
and surface normals.
A point is a position in 3D space. A vector has a length and direction, but does not exist in
a particular location. A normal is a special type of vector that is perpendicular to a surface,
and thus describes the surface’s orientation.
All calculations involving points, vectors, and normals are assumed to take place in an
implementation-dependent coordinate system, usually either the camera or world coordinate
system. Procedures exist to transform points, vectors, and normals from the shading coordinate
system to various named coordinate systems, or to define a point, vector, or normal
in one of several coordinate systems and transform it to the shading coordinate system. It
should be noted that point locations, direction vectors, and normals do not transform in
the same way, and therefore it is important to use the correct transformation routine for
each type.
A number of standard coordinate systems are known to a shader. These include: ”raster”,
”NDC”, ”screen”, ”camera”, ”world”, and ”object”. These are discussed in the section on
Camera in Part I. In addition, a shader knows the coordinate systems shown in Table 11.2,
Point Coordinate Systems.
Point-like variables are declared:
point u, v=1, w=point(1,1,1);
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