/* I took wave's lead and renamed brickper to DPBrickperturb.sl -- tal AT renderman DOT org */

/* 
 * brickper.sl
 *
 * AUTHOR: Darwyn Peachy
 *
 * REFERENCES:
 *    _Texturing and Modeling: A Procedural Approach_, by David S. Ebert, ed.,
 *    F. Kenton Musgrave, Darwyn Peachey, Ken Perlin, and Steven Worley.
 *    Academic Press, 1994.  ISBN 0-12-228760-6.
 */
 
#include "DPProctext.h"

#define BRICKWIDTH      0.25
#define BRICKHEIGHT     0.08
#define MORTARTHICKNESS 0.01

#define BMWIDTH         (BRICKWIDTH+MORTARTHICKNESS)
#define BMHEIGHT        (BRICKHEIGHT+MORTARTHICKNESS)
#define MWF             (MORTARTHICKNESS*0.5/BMWIDTH)
#define MHF             (MORTARTHICKNESS*0.5/BMHEIGHT)

surface
DPBrickperturb(
    uniform float Ka = 1;
    uniform float Kd = 1;
    uniform color Cbrick = color (0.5, 0.15, 0.14);
    uniform color Cmortar = color (0.5, 0.5, 0.5);
     )
{
    color Ct;
    point Nf;
    float ss, tt, sbrick, tbrick, w, h;
    float scoord = s;
    float tcoord = t;

    Nf = normalize(faceforward(N, I));

    ss = scoord / BMWIDTH;
    tt = tcoord / BMHEIGHT;

    if (mod(tt*0.5,1) > 0.5)
        ss += 0.5;  /* shift alternate rows */
    tbrick = floor(tt); /* which brick? */
    ss += 0.1 * snoise(tbrick+0.5);
    sbrick = floor(ss); /* which brick? */
    ss -= sbrick;
    tt -= tbrick;
    w = step(MWF,ss) - step(1-MWF,ss);
    h = step(MHF,tt) - step(1-MHF,tt);

    Ct = mix(Cmortar, Cbrick, w*h);

    /* diffuse reflection model */
    Oi = Os;
    Ci = Os * Ct * (Ka * ambient() + Kd * diffuse(Nf));
}