The RenderMan Interface - Paul Bourke

}
return 2 * (vector noise(p)) - 1;
Functions may be declared anyplace that it is legal to declare a variable or have any other
language statement, including inside the body of a shader, inside another function, or inside
any other code block. A function may only be called within the lexical scope in which
it is declared, and only after its declaration (the same rules that apply to using a declared
variable). The only data that functions may access are those passed as parameters, except
for variables declared with the extern keyword, which indicates that the variable is in an
outer scope rather than that local storage should be allocated. For example:
surface mysurf (float Knoise = 0.5;) /* parameter */
{
color shadernoise (point p)
{
extern float Knoise;
return Knoise * color noise (transform (”shader”, p));
}
}
/* code for the shader */
Ci = shadernoise(P) * diffuse(faceforward(normalize(N),I));
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