The RenderMan Interface - Paul Bourke

15.7.3 Shadow depth maps
Shadow depth maps are z-buffer images as seen from a particular view point. Normally a
shadow map is associated with a light source and represents a depth buffer rendered from
the point of view of the light source. The texture coordinate of a shadow map is a point.
The value returned is the fraction of points on the shaded surface that are farther from the
light than the surface recorded in the depth map. A value of 1 indicates that the surface is
completely in shadow and a value of 0 indicates that the surface is completely illuminated
by the light source.
float shadow( string name[channel]; texture coordinates[, parameterlist] )
where texture coordinates is one of the following:
point P;
point P1, P2, P3, P4;
Return the shadow value from a shadow depth map. The name is the name of the
texture map created using RiMakeShadow. The channel selector is optional; if it is
not present, the brackets are also omitted and channel 0 is assumed. channel selects
the starting channel in the texture. Only one channel of a shadow map is ever accessed.
texture coordinates are points in the coordinate system in which the depth
map was created. parameterlist is a list of name-value pairs that allow greater control
over texture access.
15.7.4 Getting Information About Texture Maps
float textureinfo ( string texturename, dataname; output type variable )
Returns data that about a particular texture map, specified by the file name texturename.
The dataname specifies the piece of information that will be returned in variable.
The dataname is known to the renderer and its type and storage class match
that of variable, the named data will be written into variable and textureinfo() will
return a value of 1.0. If the data is unknown or the types do not match, variable will
be unchanged and textureinfo() will return 0.0. Note that textureinfo data is always
uniform. If variable is varying, the appropriate uniform-to-varying conversion will
take place.
The standard data names supported by textureinfo are listed in Table 15.3. A particular
implementation may support additional textureinfo queries.
15.8 Message Passing and Information Functions
float atmosphere( string paramname; output type variable )
float displacement( string paramname; output type variable )
float lightsource( string paramname; output type variable )
float surface( string paramname; output type variable )
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