i have a small ellipse which bounces around in the space and a large ellipse in the center that does not move. how do i make the little ellipse bounce off the big ellipse when it hits it?


Idea ideas;
int size = 60;       // Width of the shape
float xpos, ypos;    // Starting position of shape   

float xspeed = 2.8;  // Speed of the shape
float yspeed = 2.2;  // Speed of the shape

int xdirection = 1;  // Left or Right
int ydirection = 1;  // Top to Bottom


void setup() {
  size (800, 800);
  smooth ();
  strokeWeight (2);
 

   xpos = width/2;
  ypos = height/2;
 
 
}

// ------------------------------------------------------------------------------ Main methods
void draw () {
  background (100);
  ellipse (width/2, height/2, 400, 400);
  xpos = xpos + ( xspeed * xdirection );
  ypos = ypos + ( yspeed * ydirection );
 
  if (xpos > width-size || xpos < 0) {
    xdirection *= -1;
  }
  if (ypos > height-size || ypos < 0) {
    ydirection *= -1;
  }


  ellipse(xpos+size/2, ypos+size/2, size, size);
 
}