Checkerboard.pde

// https://openprocessing.org/sketch/20534/#

int dim = 50;
int interval = int(dim * 0.4);

void setup() {
  size (500, 500);
  println(dim + ", " + interval);
  noStroke();
}

void draw() {
  for (int h = 0; h < width; h += dim) {
    for (int v = 0; v < height; v += dim) {    
      if ((h + v) % interval == 0) {  
        fill(150, 0, 0); 
      } else { 
        fill(0); 
      } 
      rect (h, v, dim, dim);
    }
  }
}