--- ray/src/rt/rayinit.cal	1993/03/18 12:36:03	2.6
+++ ray/src/rt/rayinit.cal	1995/08/25 11:43:29	2.9
@@ -24,6 +24,10 @@
  	RdotP				- perturbed ray dot product
  	CrP, CgP, CbP			- perturbed material color
 
+	For prism1 and prism2 types, the following are available:
+
+	DxA, DyA, DzA			- direction to target light source
+
 	Library functions:
 
 	if(a, b, c)			- if a positive, return b, else c
@@ -67,6 +71,7 @@ noise3d(i,x,y,z) = select(i, noise3a(x,y,z), noise3b(x
 bound(a,x,b) : if(a-x, a, if(x-b, b, x));
 Acos(x) : acos(bound(-1,x,1));
 Asin(x) : asin(bound(-1,x,1));
+Atan2(y,x) : if(x*x+y*y, atan2(y,x), 0);
 Exp(x) : if(-x-100, 0, exp(x));
 Sqrt(x) : if(x, sqrt(x), 0);
 
@@ -144,7 +149,7 @@ nrand(x) = unif2norm(rand(x));
 
 			{ Local (u,v) coordinates for planar surfaces }
 crosslen`private = Nx*Nx + Ny*Ny;
-			{ U is distance from origin in XY-plane }
+			{ U is distance from projected Z-axis }
 U = if( crosslen`private - FTINY,
 		(Py*Nx - Px*Ny)/crosslen`private,
 		Px);