Re: Lunar Lander

On 10/24/2012 6:32 PM, sqwundle@gmail.com wrote:


You've got a lot of problems. You need a more workable structure for
your drawing code. Calling repaint() from your paint() method is
problematic. You need a Thread or a Timer that calls repaint() after
you change your velocities. Lew's suggestion to use Swing would make
things easier and probably make it work better tool.

The javax.swing.Timer class is very easy to use for your animation loop.
  You can use the arrow keys to increment or decrement your velocities.
  Then in each actionPerformed() of the Timer, redraw your lander's world.

Here is some simpler code for you to emulate;

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;

public class test1 extends JPanel implements ActionListener {
     private volatile int x = 200, y = 150;
     private volatile int dx = 0, dy = 0;

     private final Timer timer;

     public test1() {
         setPreferredSize(new Dimension(400,300));

         addKeyListener(new KeyAdapter() {
             public void keyPressed(KeyEvent ke) {
                 int code = ke.getKeyCode();
                 switch (code) {
                     case KeyEvent.VK_UP:
                         dy -= 1;
                         break;
                     case KeyEvent.VK_DOWN:
                         dy += 1;
                         break;
                     case KeyEvent.VK_LEFT:
                         dx -= 1;
                         break;
                     case KeyEvent.VK_RIGHT:
                         dx += 1;
                         break;
                 }
             }
         });

         timer = new Timer(40,this); // 25 frames per second
     }

     public void start() {
         timer.start();
     }

     public void actionPerformed(ActionEvent ae) {
         x += dx;
         y += dy;
         repaint();
     }

     public void paintComponent(Graphics g) {
         g.setColor(getBackground());
         g.fillRect(0,0,getWidth(),getHeight());
         g.setColor(Color.RED);
         g.drawString(String.format("X:%04d Y:%04d dX:%04d
dY:%04d",x,y,dx,dy),
          10,10);
         g.fillOval(x-2,y-2,5,5);
     }

     public static void main(String[] args) {
         EventQueue.invokeLater(new Runnable() {
             public void run() {
                 test1 t1 = new test1();
                 JFrame f = new JFrame("test1");
                 f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                 f.add(t1,BorderLayout.CENTER);
                 f.pack();
                 f.setVisible(true);
                 t1.start();
                 t1.requestFocusInWindow();
             }
         });
     }
}

--

Knute Johnson