float myAngle = 0;

void setup(){
  size(640, 360);
  background(0);
  noStroke();
  colorMode(HSB);
}

void draw(){

  fill(random(255),255,255);

  //translate(width/2,height/2);
  pushMatrix();
  translate(width/2, height/2);
  rotate(myAngle);
  rectMode(CENTER);
  //rect(0, 0, mouseX, mouseX);
  rect(0, 0, sin(myAngle/100)*400, sin(myAngle/100)*400);
  myAngle++;
  popMatrix();
  fill(0,1);
  rect(width/2,height/2,width,height);
}