let angle = 0;

let angle_change = 1;

​

function setup() {

  createCanvas(400, 400);

  rectMode(CENTER); // this line will make the (x,y) coordinate of the rectangle be the center (not the top left corner)

  angleMode(DEGREES);

}

​

function draw() {

  background(50);

  // adding one to the angle of rotation

  if (mouseIsPressed == true) {

    angle = angle + angle_change;

  }

​

  if (angle > 60) {

    angle_change = angle_change * -1;

  }

  if (angle < 0) {

    angle_change = angle_change * -1;

  }

​

  push(); // starting the transformation

    translate(200, 200);  // setting the point of rotation to 200, 200

    rotate(angle);  // using the variable angle in rotate

    fill(255);

    noStroke();

    rect(0,0, 100, 100);

​

  pop(); // ending the rotation

}

​

​