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(640, 200);
    noStroke();
    frameRate(30);
    smooth();
    // Set the starting position of the shape
    xpos = width/2;
    ypos = height/2;
  }
  
  void draw() 
  {
    background(102);
    
    // Update the position of the shape
    xpos = xpos + ( xspeed * xdirection );
    ypos = ypos + ( yspeed * ydirection );
    
    // Test to see if the shape exceeds the boundaries of the screen
    // If it does, reverse its direction by multiplying by -1
    if (xpos > width-size || xpos < 0) {
      xdirection *= -1;
    }
    if (ypos > height-size || ypos < 0) {
      ydirection *= -1;
    }
  
    // Draw the shape
    ellipse(xpos+size/2, ypos+size/2, size, size);
  }