The RenderMan Interface - Paul Bourke

Type
Light sources
Surfaces
Atmosphere
Displacement
Imager
Shader
ambientlight
distantlight
pointlight
spotlight
constant
matte
metal
shinymetal
plastic
paintedplastic
fog
depthcue
bumpy
background
Table 10.1: Standard Shaders
Shaders contain instance variables that customize a particular shader of that type. For a
surface shader these variables may denote material properties; for a light source shader
these variables may control its intensity or directional properties. All instance variables
have default values that are specified in the definition of the shader. When a shader is
added to the graphics state, these default values may be overridden by user-supplied values.
This is done by giving a parameter list consisting of name-value pairs. The names in
this list are the same as the names of the instance variables in the shader definition. Note
that many different versions of the same shader can be instanced by giving different values
for its instance variables. The instance variables associated with a shader effectively
enlarge the current graphics state to include new appearance attributes. Because the attributes
in the graphics state are so easily extended in this way, the number of “built-in” or
“predefined” shading-related variables in the graphics state has been kept to a minimum.
There are several steps involved in using a shader defined in the Shading Language. First,
a text file containing the source for the shader is created and edited. Second, this file is
then compiled using the Shading Language compiler to create an object file. Third, the
object file is placed in a standard place to make it available to the renderer. At this point, a
shader programmed in the Shading Language is equivalent to any other shader used by the
system. When a RenderMan Interface command involving a programmed shader (that is,
one that is not built-in) is invoked, the shader is looked up by name in the table of available
shaders, read into the rendering program, and initialized. This shader is then instanced
using the instance variables supplied in the RenderMan Interface procedure. Finally, when
a geometric primitive is being shaded, the shaders associated with it are executed.
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