let rotation_speed = 0.01;

​

function setup() {

  createCanvas(400, 400);

​

  // set the origin point for the rect() to its center

  rectMode(CENTER);

}

​

function draw() {  

  background(100, 0, 200);

  strokeWeight(10)

​

  // move everything to the center of the canvas

  translate(width/2, height/2);

  // rotate the rect()

  rotate(rotation_amount);

  stroke(255, 0, 255);

  fill(255, 0, 0);

  rect(0, 0, 100, 100);

  // rotate the line() twice as fast

  rotate(rotation_amount * 2);

​

  stroke(0, 200, 255);

  line(0, 0, 0, 100)

  // increase the rotation value

  rotation_amount += rotation_speed;

}