/***********************************************************************
 * Tom Kelliher
 * CS 245
 * Bounce1.java
 *
 * This applet is a first pass at controlling a bouncing ball via a
 * moded start/stop button.
 *
 * Question to be answered: Explain precisely why the applet never
 * responds to clicks on the stop button.
 ***********************************************************************/


import java.applet.*;
import java.awt.*;
import java.awt.event.*;


public class Bounce1 extends Applet implements ActionListener
{
    private Canvas display = new Canvas();  // Ball rendered here.
    private Button startStop = new Button("Start");
    private Ball ball = null;


    public void init()
    {
        setLayout(new BorderLayout());
        add("South", startStop);
        add("Center", display);
        startStop.addActionListener(this);
    }

    
    public void actionPerformed(ActionEvent e)
    {
        if (startStop.getLabel().equals("Start"))
        {
            startStop.setLabel("Stop");  // Change button mode.
            ball = new Ball(display, Color.red);

            // Render the ball.

            ball.draw(Color.black);

            //Continue moving and rendering the ball.

            while (startStop.getLabel().equals("Stop"))
                ball.move();
        }
        else
            // Note: we are no longer rendering the ball.
            startStop.setLabel("Start");
    }
}


/***********************************************************************
 * class Ball --- implements a bouncing ball.
 ***********************************************************************/

class Ball
{
    private Canvas theCanvas;  // Reference to our drawing surface.
    private Color color;       // Color of this ball.
    private int x, y;          // Position of this ball.
    private double velocity;   // X-velocity of this ball.
    final static int DELAY = 1000000;  // Spin-loop delay factor.

    
/***********************************************************************
 * public Ball(Canvas c, Color co) --- c is the drawing surface, co is
 *    the color in which to render the ball.
 ***********************************************************************/

    public Ball(Canvas c, Color co)
    {
        theCanvas = c;
        color = co;
        x = c.getWidth() / 2;

        // Set random y and x-velocity factors.

        y = (int) (10 + (c.getHeight() - 20) * Math.random());
        velocity = 0.6 + Math.round(2.5 * Math.random());
    }


/***********************************************************************
 * public void draw(Color c) --- Render a 10 pixel ball as its current
 *    position in color c.
 ***********************************************************************/

    public void draw(Color c)
    {
        Graphics g = theCanvas.getGraphics();
        g.setColor(c);
        g.fillOval(x, y, 10, 10);
        g.dispose();
    }


/***********************************************************************
 * public void move() --- Paint over the ball in its former location,
 *    update to its new position, and render.
 ***********************************************************************/

    public void move()
    {
        // Delay in spin-loop.
        for (int i = 0; i < DELAY; ++i)
            ;
        
        // Erase former position.

        draw(Color.white);
        
        if (x <= 0 || x >= theCanvas.getWidth())
            velocity = -velocity;

        // Update x coordinate.

        x = (int) (Math.round(x + velocity));

        // Render ball at new position.

        draw(color);
    }
}