Problem: movement of Asteroids clone Ship

Newbie & Debugging Questions
#1

Hi,

I’m in the process of making a 2D Asteroids clone.

I’ve managed to rotate and translate (move with the correct orientation) the ship with:

	public void paintComponent(Graphics g){
		super.paintComponent(g);
		setBackground(Color.black);

		// Cast Graphics to Graphics2D
 		Graphics2D g2d = (Graphics2D)g;

		[b]//Moves ship[/b]
		g2d.translate(shipVelocity.x, shipVelocity.y);

		[b]//Rotates ship[/b]
		g2d.rotate(rotate.getTheta(), ship.getX(), ship.getY());

My problem is that I want the ship to continue moving (translating) without further input from the up arrow. I need to do it with the

public void actionPerformed(ActionEvent e)

method and a Timer object. Would anyone know how to do this? I also tried placing AffineTransform() methods into the public void actionPerformed(ActionEvent e) method but I don’t think that it was the right approach.

I’ve come close to achieving the movement of the ship with updating the polygons of the ship:

	public void actionPerformed(ActionEvent e) {
		      if (up && t.isRunning()) {
			    [b] ship.move(shipVelocity.x, shipVelocity.y);[/b]
                      }
             repaint();
             }
	     public void keyPressed(KeyEvent e) {
		      t.start();
		      if (e.getKeyCode() == KeyEvent.VK_UP) {
			     [b]shipVelocity.x += SHIP_THRUST_SPEED * Math.cos(rotate.getTheta());
      		             shipVelocity.y += SHIP_THRUST_SPEED * Math.sin(rotate.getTheta());[/b]
                      } 
              }

//Ship class:

public void [b]move[/b](double dx, double dy) {
x += dx;
y += dy;

// updates the already constructed polygons

hull = new Polygon();
hull.addPoint( 0+x, 15+y );
hull.addPoint( -10+x, -15+y );
hull.addPoint( -5+x, -10+y );
hull.addPoint( 5+x, -10+y );
hull.addPoint( 10+x, -15+y );
hull.addPoint( 0+x, 15+y );

cockpit = new Polygon();
cockpit.addPoint( 0+x, 6+y );
cockpit.addPoint( -4+x, -6+y );
cockpit.addPoint( 0+x, -8+y );
cockpit.addPoint ( 4+x, -6+y );

thrust = new Polygon();
thrust.addPoint( -5+x, -10+y );
thrust.addPoint( -0+x, -20+y );
thrust.addPoint( 5+x, -10+y );

The only thing is the movement is warped and doesn’t move like the g2d.translate(shipVelocity.x, shipVelocity.y); method.

Also, any ideas on that effect in Asteroids where when you move the ship to the side of one screen boundary it gets translated to the opposite end of the screen?

Kind regards,

Hendrick

#2

I suppose you’re on the good way, but you need to know a thing or 2 about a game’s technical architechture. The way you’re approaching how to make a game is a common beginners mistake so to speak, i started exactly the same way :wink: First, just don’t make it difficult for yourself by using threads, and second, you dont want to use Timer stuff.

The point with using repaint(), is that its not an order to java to repaint, but actually a request, which java will answer to when the jvm has the time to comply. Therefor you will have to take these matters into your own hand. Where you want to go, is to a general so called main loop where you check and process your input, and render your graphics every pass, which is normally called a frame. A basic mainloop looks a bit like this;


public void mainLoop() {
    while(running) {
         handleInput();
         doMovement(); 
         drawFrame();
    }
}

You would also go for accelerated graphics. This allows to prepare the next batch of graphics while the current is being displayed basicly, and it wil help on creating more fluency in movement.

What youd best go from here, is prolly to read Kevin Glass his Space Invaders Tutorial, where every aspect is explained a bit better :wink: You could also read the book “Killer Game Programming In Java”.