The RenderMan Interface - Paul Bourke

diffuse returns the diffuse component of the lighting model. N is a unit-length surface
normal.
color
specular( normal N; vector V; float roughness )
{
color C = 0;
illuminance( P, N, PI/2 )
C += Cl * specularbrdf (normalize(L), N, V, roughness);
return C;
}
specular returns the specular component of the lighting model, using an implementationdependent
specularbrdf. N is the unit-length normal to the surface. V is a unit-length
vector from a point on the surface towards the viewer.
color specularbrdf ( vector L; normal N; vector V; float roughness )
Returns the specular attenuation of light coming from the direction L, reflecting toward
direction V , with surface normal N and roughness rough. All of L, V , and N
are assumed to be of unit length. This is the same reflection model calculation found
inside the illuminance loop of the specular function. This allows users to write an
illuminance loop that reproduces the functionality of the specular() function, even if
the renderer has an implementation-specific formula for built-in specular reflection.
Here is an example implementation of specularbrdf:
color specularbrdf( vector L, N, V; float roughness )
{
vector H = normalize(L+V);
return pow (max (0, N.H), 1/roughness);
}
color
phong( normal N; vector V; float size )
{
color C = 0;
vector R = reflect( -normalize(V), normalize(N) );
illuminance( P, N, PI/2 ) {
vector Ln = normalize(L);
C += Cl * pow(max(0.0,R.Ln), size);
}
return C;
}
phong implements the Phong specular lighting model.
color trace( point P, point R )
trace returns the incident light reaching a point P from a given direction R. If a particular
implementation does not support the Ray Tracing capability, and cannot compute
the incident light arriving from an arbitrary direction, trace will return 0 (black).
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