// bounce

// Copyright © 2011 Mark F. Russo
// Bryn Mawr College, Department of Computer Science
// Permission is granted to copy and distribute provided 
// this entire copyright notice is reproduced in all copies.

float sx = 0.0;    // x position
float sy = 0.0;    // y position
float vx = 1.0;    // x velocity
float vy = 1.0;    // y velocity
float ay = 0.2;    // y acceleration (gravity)

void setup() {
  size(500, 500);
  fill(255, 0, 0);
  smooth();
  ellipseMode(CENTER);
}

void draw() {
  // Equations of Motion
  sx = sx + vx;
  sy = sy + vy;
  vy = vy + ay;

  // Bounce off walls
  if (sx <= 0.0 || sx >= width) vx = -vx;
  
  // Bounce off floor and
  // lose some velocity due to friction
  if (sy >= (height-10.0)) vy = -0.9*vy;
  
  // Draw at current location
  background(255);
  ellipse(sx, sy, 20, 20);
}