// Bubbles
function setup() {
  createCanvas(400, 400);
}

function draw() {
  background(255);
  fill('green')
  rect(0, 0, 200, 400);
  fill(0)
  rect(200, 0, 200, 400);
  
  blendMode(DIFFERENCE);
  fill('green');
  noStroke();
  noCursor()
  circle(mouseX, mouseY, 40)
  
  blendMode(BLEND);
}