Checkerboard Pattern

checkerboard.pde

void setup () {
  size (400, 400);
}

void draw () {
  background (0);
  int spacing = 10;
  noStroke();
  int cols = width / spacing;
  int rows = height / spacing;
  for (int x = 0; x < cols; x = x + 1) {
    for (int y = 0; y < rows; y = y + 1) {
      if ((x % 2 == 0 && y % 2 == 1) || (x % 2 == 1 && y %2 == 0)) {
        fill(255);
      } else {
        fill(0);
      }
      rect (x*spacing, y*spacing, spacing, spacing);
    }
  }
}