/*
* checks_aa.sl -- RenderMan compatible shader for checks.
*
* DESCRIPTION:
* Makes a checkered surface, fully antialiased! This sucker should
* look great even at only one sample per pixel.
*
* PARAMETERS:
* Ka, Kd work just like the matte shader
* color1, color2 these are the colors which make the pattern
* frequency determines the frequency (in s-t space) of the checks
*
*
* AUTHOR: written by Larry Gritz
*
* HISTORY:
* 27 Jan 1994 -- written by lg
*
* last modified 27 Jan 1994 by Larry Gritz
*/
surface
LGAntialiasedChecks (float Ka = 1, Kd = 1, frequency = 10;
color color1 = 0, color2 = 1; )
{
point Nf; /* Forward facing surface normal */
float smod, tmod; /* Texture position within the pattern */
color checkcolor; /* Color of the checks */
float x, y; /* Used to determine pattern */
float swidth, twidth, sfuzz, tfuzz; /* Antialiasing */
float Nfactor; /* Multiplicative factor for AA due to normal */
float fuzzmax; /* max of (sfuzz, tfuzz) */
Nf = faceforward (normalize(N), I);
/* Determine how wide in s-t space one pixel projects to */
swidth = abs(Du(s)*du) + abs(Dv(s)*dv);
twidth = abs(Du(t)*du) + abs(Dv(t)*dv);
/* Figure out amount of fuzziness, taking normal into account */
Nfactor = abs (Nf . I) / (length(Nf) * length(I));
sfuzz = .5 * swidth * frequency / Nfactor;
tfuzz = .5 * twidth * frequency / Nfactor;
fuzzmax = max (sfuzz, tfuzz);
/* Get the place in the pattern where we're sampling */
smod = mod (s*frequency, 1);
tmod = mod (t*frequency, 1);
/* If the filter width is small enough, compute the pattern color */
if (fuzzmax <= 0.5) {
x = ((smoothstep (.5,.5+sfuzz,smod)) + (1 - smoothstep (0,sfuzz,smod)));
y = ((smoothstep (.5,.5+tfuzz,tmod)) + (1 - smoothstep (0,tfuzz,tmod)));
checkcolor = mix (color1, color2, x*y + (1-x)*(1-y));
/* Gradually fade in the average color when we get close to the limit */
Ci = mix (checkcolor, (color1+color2)/2, smoothstep (.125, .5, fuzzmax));
}
else { /* otherwise, only use the average color */
Ci = (color1 + color2) / 2;
}
/* Use the matte reflectance formula */
Oi = Os;
Ci *= Os * (Ka*ambient() + Kd*diffuse(Nf));
}