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);
		}
	}
}