====== Implementing a Simple Single Keystroke Menu ======

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The following version of SpriteDemoPanel implements an on-screen menu that allows you to choose a level of snowfall or to Quit when the animation starts. The animation also listens for an Esc key press to return to the menu.

  * [[http://rockhopper.monmouth.edu/~jchung/cs498gd/fa13/labs/menu/simple_kb/snow_slow_sprite_menu.zip | Complete zip archive of animation source]]

<code>
/*
 * Modified for simple, single-keystroke menu (jchung, 11/2011)
 */

/*
 * Modified for Snowflake sprites (jchung)
 */

/*
 * Description: Demo with sprites (Updated on July 19, 2009)
 */

import java.awt.*;
import java.awt.image.*;    // for BufferedImage.
import java.io.*;           // to read Files.
import javax.imageio.*;     // to load image below.
import java.util.*;
import java.awt.event.*;    // for FocusListner, KeyListener
import javax.swing.*;


// FocusListener, KeyListener added for kb event handling:
public class SpriteDemoPanel extends JPanel implements Runnable, FocusListener, KeyListener {
    private static final long serialVersionUID = 1L;
    public static final int MAX_SPRITES = 30;
    private Thread animator;
    private int fps, frame, delay;
    private GameSprite [] sprites;
    // Added on-screen menu
    private boolean menuOn;
    private Font f = new Font("monospaced", Font.BOLD, 20);
    // Added menu-driven number of snowflakes
    private int numSnowflakes;

    // Panel background:
    BufferedImage background;

    // Snowflake crosswind:
    double wind;
    double windx;    // how much to change wind value by

    private void initSprites() {
        sprites = new GameSprite[MAX_SPRITES];
        RandomCoordinates randCoords = new RandomCoordinates(MAX_SPRITES);
        Random generator = new Random();

        for (int count = 0; count < MAX_SPRITES; count++) {
            sprites[count] = new
            SnowflakeSprite( (double) randCoords.getXCoordAt(count), (double) randCoords.getYCoordAt(count), fps);
               // Now passing fps to Sprites.
        }
    }

    



    // This constructor is not used:
    public SpriteDemoPanel() {
        fps = 30;
        delay = (1000 / fps);
        initSprites();

        // setDoubleBuffered applies to this JPanel.
        setDoubleBuffered( true );
    }





    // This constructor is used:
    public SpriteDemoPanel (int initFPS) {
        fps = initFPS;
        delay = (1000 / fps);
        initSprites();

        // Read the background.png image in current directory:
        try {
            background = ImageIO.read( new File( "background.png" ) );
        } catch (Exception ex) {}

        setDoubleBuffered( true );

        // to handle keyboard events:
        addFocusListener(this);
        addKeyListener(this);
        setFocusable(true);

        // Start with on-screen menu:
        menuOn = true;
    }






    public void paintComponent (Graphics g) {
        // Clear the panel:
        // g.clearRect(0, 0, this.getWidth(), this.getHeight());

        // Instead of clearing the panel, draw a background image instead:
        g.drawImage( background, 0, 0, null );

        // Added the on-screen menu; when the menu's on, stop the snow:
        if (menuOn) {
            g.setFont(f);
            g.setColor(Color.WHITE );
            g.drawString("1) Flurry", 200, 300);
            g.drawString("2) Fall", 200, 350);
            g.drawString("3) Blizzard", 200, 400);
            g.drawString("4) Quit", 200, 450);
        }
        else {
           // Draw numSnowflakes snowflakes, where numSprites is set by the
           // menu choices above:
           for (int count=0; count < numSnowflakes; count++)
               sprites[count].drawSprite(g);
        }
    }






    public void start() {
        animator = new Thread(this);
        animator.start();
    }

    public void stop() {
        animator = null;
    }

    public void run() {
        long start = System.currentTimeMillis();
        Thread current = Thread.currentThread();

        while (current == animator) {
            try {
                // Delay depending on how far we are behind
                start += delay;
                Thread.sleep(Math.max(0, start - System.currentTimeMillis()));
            } catch (InterruptedException e) {
                System.err.println("An error occurred: " + e.toString());
                e.printStackTrace();
            }

            // Draw the frame
            repaint();

            // Update the sprites
            for (int count = 0; count < MAX_SPRITES; count++) {
                sprites[count].updateSprite();
                sprites[count].moveSprite();
            }

            // Figure out how fast it is running
            if (start + 1000 < System.currentTimeMillis()) {
                start = System.currentTimeMillis();
            }

            // Advance the frame
            frame++;
        }
    }






    public void keyPressed (KeyEvent e) {
        // Will try to emulate a crosswind effect on snowflakes with
        // left/right arrow keys.  Shift+<arrow> makes for stronger
        // crosswind.

        int key = e.getKeyCode();  // Keyboard code for the key that was pressed

        // windx is in pixels per second:
        if ( e.isShiftDown() )
            windx = 30.0;
        else
            windx = 10.0;

        switch (key) {
           case (KeyEvent.VK_LEFT):
               wind = wind - windx;
               break;
           case (KeyEvent.VK_RIGHT):
               wind = wind + windx;
               break;
           case (KeyEvent.VK_ESCAPE): // Escape to menu
               menuOn = true;
               break;
           case (KeyEvent.VK_1):      // Process menu options
               numSnowflakes = 10;
               menuOn = false;
               break;
           case (KeyEvent.VK_2):
               numSnowflakes = 20;
               menuOn = false;
               break;
           case (KeyEvent.VK_3):
               numSnowflakes = MAX_SPRITES;
               menuOn = false;
               break;
           case (KeyEvent.VK_4):
               System.exit(0);
        }

        for (int count = 0; count < MAX_SPRITES; count++)
            sprites[count].setXspeed( wind );

        repaint();
    }

    public void keyTyped (KeyEvent e) {}

    public void keyReleased (KeyEvent e) {}

    public void focusGained (FocusEvent e) {}

    public void focusLost (FocusEvent e) {}
}
</code>

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