Source Code:            Syntax: C#

// Bounce
// by REAS <http://reas.com>

// When the shape hits the edge of the window, it reverses its direction

// Updated 1 September 2002

int iSize = 60;       // Width of the shape
double xpos, ypos;    // Starting position of shape    

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

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


public override void setup() 
{
  size(200, 200);
  noStroke();
  framerate(30);
  smooth();
  // Set the starting position of the shape
  xpos = width/2;
  ypos = height/2;
}

public override 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-iSize || xpos < 0) {
    xdirection *= -1;
  }
  if (ypos > height-iSize || ypos < 0) {
    ydirection *= -1;
  }

  // Draw the shape
  ellipse(xpos+iSize/2, ypos+iSize/2, iSize, iSize);
}