The RenderMan Interface - Paul Bourke

Return a unit vector in the direction of V .
float
distance( point P1, P2 )
{
return length(P1-P2);
}
Return the distance between two points.
float ptlined ( point Q, P1, P2 )
Returns the minimum perpendicular distance between the point Q and the line segment
that passes from the point P0 to the point P1 (not the infinite line which passes
through P0 and P1).
float rotate ( point Q; float angle; point P1, P2 )
Rotate a point Q by angle radians about the axis which passes through the points P0
and P1.
float
area( point P )
{
return length( Du(P)*du ˆ Dv(P)*dv);
}
Return the differential surface area.
vector
faceforward( vector N, I [, Nref])
{
return sign(-I.Ng) * N;
}
Flip N so that it faces in the direction opposite to I, from the point of view of the
current surface element. The surface element’s point of view is the geometric normal
Ng, unless Nref is supplied, in which case it is used instead.
vector
reflect( vector I, N )
{
return I - 2*(I.N)*N;
}
Return the reflection vector given an incident direction I and a normal vector N.
vector
refract( vector I, N; float eta )
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