grid

int step = 80;

void setup() {
  size(800, 640);
  background(255);
  strokeCap(SQUARE);

  drawGrid();

}

void draw() {
}

void mouseClicked() {
  setup();
}

void keyPressed() {
  save(random(1234)+".png");
}

void drawGrid() {

  for (int x=step; x<width; x += step) {
    for (int y=step; y<height; y += step) {
      noFill();
      int c = 0;
      strokeWeight(step/4);
      for (int i=0; i<4; i++) {
        float r = random(1);
        if (r > .25) {
          stroke(0);
          c++;
        }
        else {
          noStroke();
        }
        arc(x, y, step, step, (i*PI/2)-0.01, ((i+1)*PI/2)+0.01);
        if (c==4) {
          fill(200);
          strokeWeight(3);
          //ellipse(x, y, step*.75, step*.75);
        }
      }
    }
  }
}