convection on http://syzygy.st

gistfile1.js

for (var v = 0; v < 2*N; v++) {
  for (var u = -N; u < N; u++) {
    var w = getCube(u, v);
    if (w > 0 && w < tick) { // there's a cube and it's not one we just created
      setCube(u, v, 0); // remove it
      if (u < N && v > 0) {
        if (Math.random() < 0.5) // 50% of the time
          setCube(u + 1, v - 1, tick); // directly above
        if (Math.random() < 0.25) // 25% of the time
          setCube(u + 1, v - 2, tick); // above-left
        if (Math.random() < 0.25) // 25% of the time
          setCube(u + 2, v - 1, tick); // above-right
        if (Math.random() < 0.25) // 25% of the time
          setCube(u + 2, v - 2, tick); // above-above
      }
    }
  }
}
tick++;