/**  "modulo"
 * (cc) 2006 douglas edric stanley
 * http://creativecommons.org/licenses/by/2.5/
 * This work is licensed under the Creative Commons Attribution2.5 License. To view a copy of this license, visit http://creativecommons.org/licenses/by/2.5/ or send a letter to Creative Commons, 543 Howard Street, 5th Floor, San Francisco, California, 94105, USA.
 */

int x, y;

void setup() {

  size(256,256);

  // pink lines
  stroke(255,0,255);

}

void draw() {

  // white background
  background(255);

  x += 1;                  // increment x position
  x %= width;              // this is the modulo
  line(x,0,x,height);      // draw vertical line with x

  if (x==0) y += 1;       // if x has moved back to 0, increment y position
  y %= height;            // this is the modulo
  line(0,y,width,y);      // draw horizontal line with y

}