let maskRect = 115;

​

function setup() {

  createCanvas(500, 500);

}

​

function draw() {

  background(0);

  rectMode(CENTER);

  noStroke();

  fill(255, 0, 0);

  push();

  translate(width/2,height/2);

  rotate(radians(45));

  rect(0,0, 200, 200);

  pop();

​

  fill(0);

  push();

  translate(width / 3, height / 2);

  rotate(radians(angle));

  rect(0, 0, maskRect, maskRect);

  pop();

​

  push();

  translate(width - width / 3, height / 2);

  rotate(radians(angle));

  rect(0, 0, maskRect, maskRect);

  pop();

​

  angle++;

}

​