experimental image from code

gistfile1.js

// http://www.reddit.com/r/programming/comments/lrg7f/experimental_images_from_very_short_programs/

function start() { 
 var t = pt = 0;
 clearTimeout(timer); 
 var func = ""+
    "function animate() {"                    +
    "  var x = y = pi = 0, W = w, S = size; "     +
    "  for (var i = 0; i < S;) { "            +
    "    img.data[i] = <code>; i++; t++; "    +
    "    img.data[i] = <code>; i++; t++; "    +
    "    img.data[i] = <code>; i++; t++; "    +
    "    img.data[i] = 255;    i++; t++; "    +
    "    x++; pi++; pt++; "                   +
    "    if ( x == W ) { x = 0; y++; }"       +
    "  }"                                     +
    "  <post>;"                               +
    "  ctx.putImageData(img, 0, 0);"          +
    "  timer = setTimeout(animate, 0);"       +
    "}";
 
  func = func.replace( /<code>/g, codebox.value );
  if ( inc.checked )
    func = func.replace( /<post>/g, "pt++; t++;" );
  else
    func = func.replace( /<post>/g, "t=0;" );
 eval( func );
 animate();
};