Embedding "for" structures allows repetition in two dimensions.
Original Processing.org Example: EmbeddedIteration
// All Examples Written by Casey Reas and Ben Fry // unless otherwise stated. float box_size = 11; float box_space = 12; int margin = 7; size(200, 200); background(0); noStroke(); // Draw gray boxes for(int i = margin; i < width-margin; i += box_space) { for(int j = margin; j < height-margin; j += box_space) { fill(255 - box_size*10); rect(j, i, box_size, box_size); } box_size = box_size - 0.6; }