Question

I’m writing easy space invaders and have a problem with moving ship. Basically I change position of ship and then repaint(). If the change is big it is more like jumping than moving. If the change is small animation is smoother but getting slower. Is there any solution?

I’m drawing on JPanel and using paintComponent().

@edit: I don’t really understand how my pc can display normal(new) games smoothly and with simple drawing image has low frame rate. It is why i thought it was software problem rather than hardware. So maybe i do something what affects frame rate.

@edit: Ok, pasting some code, but be understanding – I started with java and generally programming graphics about 2 weeks ago.

    package pl.spaceInvaders;
    import java.awt.Color;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.Image;
import java.awt.Insets;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.KeyEvent;
import java.awt.event.KeyListener;

import javax.swing.JPanel;
import javax.swing.Timer;

class GamePanel extends JPanel{
SpaceInvadersMain sim;
private Image dbImage; 
private Graphics dbg; 
int moveDistHor=0;
int moveDistVer=0;
int shipMove=0;
int dir=1;

GamePanel(SpaceInvadersMain sim){
    this.sim=sim;
    setFocusable(true);
    moveMonsters();
    MyKeyListener mkl = new MyKeyListener();
    addKeyListener(mkl);
    Timer t = new Timer(500, new ActionListener() {
          public void actionPerformed(ActionEvent e) {
              if(moveDistHor<304){moveDistHor+=16*dir;}
              if(moveDistHor==304 || moveDistHor==0){dir*=-1;moveDistHor+=16*dir;moveDistVer+=16;}
              moveMonsters();
              moveProjectiles();
              detectColissions();
              repaint();
          }
       });
    t.start();
}
@Override
public void paintComponent(Graphics g){
    super.paintComponent(g);
    setBackground(Color.white);
    Graphics2D g2 = (Graphics2D)g;
    Insets insets = getInsets();
    g2.translate(insets.left, insets.top);
    // drawing monsters
    for(int i=0;i<SpaceInvadersMain.M_WIDTH;i++){
        for(int j=0;j<SpaceInvadersMain.M_HIGHT;j++){
            if(sim.monsters[i][j].ifExists()){
            if((moveDistHor+moveDistVer)%32==0) 
                g2.drawImage(sim.monsters[i][j].img, sim.monsters[i][j].posX, sim.monsters[i][j].posY, 32, 32, null);
            else 
                g2.drawImage(sim.monsters[i][j].img2, sim.monsters[i][j].posX, sim.monsters[i][j].posY, 32, 32, null);
            }}
    }
    //drawing ship
    if(sim.ship.exists()) g2.drawImage(sim.ship.img, sim.ship.getPosX(), sim.ship.getPosY(),32,32,null);
}
protected void detectColissions() {
    // TODO Auto-generated method stub

}
protected void moveProjectiles() {
    // TODO Auto-generated method stub

}
protected void moveShip() {
    if(sim.ship.posX+shipMove>0 && sim.ship.posX+shipMove<750) {
        sim.ship.posX+=shipMove;
        shipMove=0;
    }

}
protected void moveMonsters(){
    for(int i=0;i<SpaceInvadersMain.M_WIDTH;i++){
        for(int j=0;j<SpaceInvadersMain.M_HIGHT;j++){
            if(sim.monsters[i][j].ifExists()){
                 sim.monsters[i][j].posX=10+i*48+moveDistHor;
                 sim.monsters[i][j].posY=10+j*48+moveDistVer;

            }}
    }
}
private class MyKeyListener implements KeyListener{

    @Override
    public void keyPressed(KeyEvent e) {
        switch(e.getKeyCode()){
        case KeyEvent.VK_LEFT:
            //System.out.println("Arrow left caught");
            shipMove=-10;
            break;
        case KeyEvent.VK_RIGHT:
            //System.out.println("Arrow right caught");
            shipMove=10;
            break;
        }
        moveShip();
        repaint();
    }

    @Override
    public void keyReleased(KeyEvent e) {

    }

    @Override
    public void keyTyped(KeyEvent e) {


    }

}

}

Answer 1

The Space Invaders – 2D Rendering in Java tutorial may be helpful as an example using an explicit BufferStrategy.