package algs11;
import stdlib.*;
/* ***********************************************************************
 *  Compilation:  javac BouncingBall.java
 *  Execution:    java BouncingBall
 *  Dependencies: StdDraw.java
 *
 *  Implementation of a 2-d bouncing ball in the box from (-1, -1) to (1, 1).
 *
 *  % java BouncingBall
 *
 *************************************************************************/

public class XBouncingBall {
  public static void main(String[] args) {

    // set the scale of the coordinate system
    StdDraw.setXscale(-1.0, 1.0);
    StdDraw.setYscale(-1.0, 1.0);

    // initial values
    double rx = 0.480, ry = 0.860;     // position
    double vx = 0.015, vy = 0.023;     // velocity
    double radius = 0.05;              // radius

    // main animation loop
    while (true)  {

      // bounce off wall according to law of elastic collision
      if (Math.abs(rx + vx) > 1.0 - radius) vx = -vx;
      if (Math.abs(ry + vy) > 1.0 - radius) vy = -vy;

      // update position
      rx = rx + vx;
      ry = ry + vy;

      // clear the background
      StdDraw.setPenColor(StdDraw.GRAY);
      StdDraw.filledSquare(0, 0, 1.0);

      // draw ball on the screen
      StdDraw.setPenColor(StdDraw.BLACK);
      StdDraw.filledCircle(rx, ry, radius);

      // display and pause for 20 ms
      StdDraw.show(20);
    }
  }
}