float x = 0;
float y = 0;
float s = 20;

void setup() {
  size(800, 800);
  background(255);
  fill(0, 100);
  smooth();
  rectMode(CENTER);
}

void draw() {
  
  s =( x+y) / 7.5;
  rect(x, y, s, s);

  x = x + 50;
  if (x > width) {
    x = 0;
    y += 50;
  }
  
}