class square
{
 float x, y, a;

 square(float xp, float yp, float ap)
 {
   x = xp; y = yp; a = ap;
 }
}

square[] sqrs = new square[4];
int a = 0, del = 10;
void setup()
{
  size(800, 600);
  frame.setResizable(true);
}

void draw() {
  float padding = 40;
  float minSide = height;
  float offsetTop, offsetLeft, rA;
  background(255);
  //calc center and sides
  if (minSide > width)
  {
    minSide = width;
    rA = minSide-padding;
    offsetTop = height - height / 2 - rA/2;
    offsetLeft = padding/2;

  }
  else
  {
    rA = minSide-padding;
    offsetLeft = width - width / 2 - rA/2;
    offsetTop = padding/2;
  }
  //calc squares pos's and sizes
  sqrs[0] = new square(offsetLeft, offsetTop, rA/2);
  sqrs[1] = new square(offsetLeft+rA/2, offsetTop, rA/2);
  sqrs[2] = new square(offsetLeft, offsetTop+rA/2, rA/2);
  sqrs[3] = new square(offsetLeft+rA/2, offsetTop+rA/2, rA/2);

  //draw squares
  /*for(int i = 0; i < 4; i++)
  {
    rect(sqrs[i].x, sqrs[i].y, sqrs[i].a, sqrs[i].a);
  }*/

  //rotate
  rotate(sqrs[0], a);
  rotate(sqrs[1], -a);
  rotate(sqrs[2], -a);
  rotate(sqrs[3], a);

  //increase angel
  if (a < 90) a++;
  else a = 0;

  delay(del);
}

void rotate(square sq, int ang)
{
  float rad, x, a1;
  boolean neg = false;
  //stab ang
  if (ang < 0) {neg = true; ang = abs(ang);}
  if (ang > 90) ang -= int(ang/90)*90;
  if (neg) ang = 90-ang;
  rad = radians(ang);
  //calculate
  x = int(sq.a/(sin(rad) + cos(rad)));
  a1 = int(x*sin(rad));
  //draw
  line(sq.x, sq.y+a1, sq.x+sq.a-a1, sq.y);
  line(sq.x+sq.a-a1, sq.y, sq.x+sq.a, sq.y+sq.a-a1);
  line(sq.x+sq.a, sq.y+sq.a-a1, sq.x+a1, sq.y+sq.a);
  line(sq.x+a1, sq.y+sq.a, sq.x, sq.y+a1);
}