int x,y,dx,dy;
float distance;

void setup(){

  size(300,300);

  noStroke();
}

void loop(){

  for(y =0 ; y < 300; y+= 60){
    for(x =0 ; x < 300; x+= 60){
    
    dx = mouseX - x;
    dy = mouseY - y;
    distance = sqrt(dx*dx + dy*dy);
    //println(distance);
    
      fill(0,distance,distance);
      rect(x,y,distance*2,distance*2);

    }
  }
}