function setup() {
  createCanvas(800, 800);
  tileWidth = width / tileCountX;
  tileHeight = height / tileCountY;
  noFill();
  stroke(0, 128);
}
changing circle amount, size and position in a grid

MOUSE
position x          : circle amount and size
position y          : circle position
left click          : random position

KEYS
s                   : save png