float x, y; // The current coordinates of the ball
float r = 20; // ball radius
float vx, vy; // ball velocity

void setup()
{
  size(400,400);
  smooth();
  noStroke();

  x = width/2; y = height/2; // start at the center
  vx = random(-5,5); vy = random(-5,5); // start in random direction
}

void draw()
{
  background(0);
  ellipse(x,y,2*r,2*r);

  // take a step
  x += vx; y += vy;
  
  // bounce if getting offscreen
  if(x != constrain(x,r,width-r)) {
    x = constrain(x,r,width-r); // constrain position
    vx = -vx;                   // flip velocity
  }
  if(y != constrain(y,r,width-r)) {
    y = constrain(y,r,width-r); // constrain position
    vy = -vy;                   // flip velocity
  }
}

// START NO NOTES
// code used to capture screenshots
void keyReleased() {
  if(key == '`' && !online) save("sketch.png");
}