/*
* screen_aa.sl -- RenderMan compatible shader for a metalic screen.
*
* DESCRIPTION:
* Makes a surface that looks like a metal screen. Strips of metal run
* parallel to lines of s and t. You can adjust the Ka, Kd, Ks, etc.
* to change the material appearance. This texture antialiases pretty
* well, even with only one sample per pixel.
*
* PARAMETERS:
* Ka, Kd, Ks, roughness, specularcolor - work just like the plastic shader
* frequency - how many cycles of screen in st space
* density - how much of each cycle is opaque?
*
* AUTHOR: written by Larry Gritz
*
* last modified 31 Jan 1994 by Larry Gritz
*
*
* The RenderMan (R) Interface Procedures and RIB Protocol are:
* Copyright 1988, 1989, Pixar. All rights reserved.
* RenderMan (R) is a registered trademark of Pixar.
*/
#define boxstep(a,b,x) (clamp(((x)-(a))/((b)-(a)),0,1))
#define MINFILTERWIDTH 1.0e-7
surface
screen_aa (float Ka = 1, Kd = 0.75, Ks = 0.4, roughness = 0.1;
color specularcolor = 1;
float density = 0.25, frequency = 20;)
{
normal Nf; /* Forward facing Normal vector */
vector IN; /* normalized incident vector */
float d; /* Density at the sample point */
float ss, tt; /* s,t, parameters in phase */
float swidth, twidth, GWF, w, h;
/* Compute a forward facing normal */
IN = normalize (I);
Nf = faceforward (normalize(N), I);
/* Determine how wide in s-t space one pixel projects to */
swidth = max (abs(Du(s)*du) + abs(Dv(s)*dv), MINFILTERWIDTH) * frequency;
twidth = max (abs(Du(t)*du) + abs(Dv(t)*dv), MINFILTERWIDTH) * frequency;
/* Figure out where in the pattern we are */
ss = mod (frequency * s, 1);
tt = mod (frequency * t, 1);
/* Figure out where the strips are. Do some simple antialiasing. */
GWF = density*0.5;
if (swidth >= 1)
w = 1 - 2*GWF;
else w = clamp (boxstep(GWF-swidth,GWF,ss), max(1-GWF/swidth,0), 1)
- clamp (boxstep(1-GWF-swidth,1-GWF,ss), 0, 2*GWF/swidth);
if (twidth >= 1)
h = 1 - 2*GWF;
else h = clamp (boxstep(GWF-twidth,GWF,tt), max(1-GWF/twidth,0),1)
- clamp (boxstep(1-GWF-twidth,1-GWF,tt), 0, 2*GWF/twidth);
/* This would be the non-antialiased version:
* w = step (GWF,ss) - step(1-GWF,ss);
* h = step (GWF,tt) - step(1-GWF,tt);
*/
d = 1 - w*h;
Oi = d;
if (d > 0) {
Ci = Oi * ( Cs * (Ka*ambient() + Kd*diffuse(Nf)) +
specularcolor * Ks*specular(Nf,-IN,roughness));
}
else
Ci = 0;
}