/* 
 title: bouncing ball 
 description: ball deflects off sketch window edges 
 created: August 9, 2005 by: Ira Greenberg 
 modified: September 6, 2006, ever so slightly, by Fred Green
 */ 
 
// declare global variables 
int xspeed, yspeed; 
int xpos, ypos, wdth, ht; 
 
//initialize sketch 
void setup(){ 
  
  //set sketch window size and background color 
  size(400, 400); 
  background(0); 
   
  //ball speed 
  xspeed = 4; 
  yspeed = 6; 
   
  //ball size 
  wdth = 20; 
  ht = 20; 
   
  // turn off shape stroke rendering 
  noStroke(); 
  
 //initial ball placement 
  xpos = width/2; 
  ypos = height/2; 
  
 //set the animation loop speed 
  frameRate(30); 
  smooth();
} 
 
// begin animation loop 
void draw(){ 
 
  //update background 
  background(0); 
 
  //draw ball
  fill(200, 200, 0);
  ellipse(xpos, ypos, wdth, ht); 
 
  //upgrade position values 
  xpos += xspeed; 
  ypos += yspeed;  
 
  /*conditionals 
    detects ball collission with sketch window edges 
    also accounts for thickness of ball 
   */ 
  if (xpos>=width-wdth/2 || xpos<=wdth/2){ 
    xspeed *= -1; 
  } 
  if (ypos>=height-ht/2 || ypos<=ht/2){ 
    yspeed *= -1; 
  } 
}