Java moving rectangle faster?

Question

So I am trying to make the popular game pong in java. I've made the player rectangle and setup the action listener so I am ready to move the player up and down on the screen. But I have run into a problem. When I am moving the player I have a choice of moving X pixels per move.

But if I set the X pixels being moved to lets say 1. Then the player is moving too slow. If I set X pixels to 10 then he skips 9 pixels and the animation looks rough. How can I smoothen the animation and still move fast?

here is some code:

public void keyPressed(KeyEvent e) {
                if(e.getKeyCode() == keyUp){
                    playerYCordinate -= 10;
                }else if(e.getKeyCode() == keyDown){
                    playerYCordinate += 10;
                }
                repaint();
            }

            public void keyReleased(KeyEvent e) {
                if(e.getKeyCode() == keyUp){

                }else if(e.getKeyCode() == keyDown){

                }
                repaint();
            }

Answer 1

Don't rely on key-repeat features provided by the system. They may occur with a low rate (which causes the problems you describe) and depend on system keyboard settings.

I recommend you to use keyPressed to start a Timer and keyReleased to stop it.

The timer could schedule to execute a TimerTask every 20:th millisecond or so, which could update the coordinates and call repaint(). (Don't worry about calling repaint() too often. If the EDT can't keep up, it will collapse consecutive calls to repaint into a single paint.)

Answer 2

How can I smoothen the animation and still move fast?

One technique is to paint semi-transparent versions of the moving object along the path it would have taken if stepping less pixels per move.

E.G. for a 10 pixel move, draw a version at 10% opacity for the 1st pixel of moving, 20% for the 2nd etc.

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

import javax.swing.*;

public class MovingBlock {

    MovingBlock() {
        final JPanel gui = new JPanel() {

            private static final long serialVersionUID = 1L;
            int x = 0;
            int step = 60;

            public void paintComponent(Graphics g) {
                super.paintComponent(g);
                Graphics2D g2 = (Graphics2D)g;
                x+=10;
                Color fg = getForeground();
                for (int ii=x-step; ii<x; ii+=4) {
                    double transparency = (double)(x-ii)/(double)step;
                    Color now = new Color(
                            fg.getRed(),
                            fg.getGreen(),
                            fg.getBlue(),
                            (int)(255*(1-transparency)));
                    g2.setColor(now);
                    g2.fillRect(ii, 3, 5, 10);
                }
                if (x>getWidth()) {
                    x=0;
                }
            }
        };
        gui.setBackground(Color.BLACK);
        gui.setForeground(Color.GREEN.darker());
        gui.setPreferredSize(new Dimension(400,16));

        ActionListener listener = new ActionListener() {
            @Override
            public void actionPerformed(ActionEvent ae) {
                gui.repaint();
            }
        };
        Timer timer = new Timer(20, listener);
        timer.start();

        JFrame f = new JFrame("Moving Block");
        f.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
        f.setContentPane(gui);
        f.pack();
        f.setLocationByPlatform(true);
        f.setVisible(true);
    }

    public static void main(String[] args) throws Exception {
        SwingUtilities.invokeLater(new Runnable() {
            public void run() {
                new MovingBlock();
            }
        });
    }
}