Java 2D "tank" game: Shooting 'missile' from rotated sprite doesn't work

Question

EDIT: Problem solved. I forgot putting Math.toRadians() anywhere I do Math.cos or Math.sin. :)

I'm working on a simple Java 2D game involving two tanks that shoot missiles and move around the screen. For this question, let's assume there's only one tank.

Controls:

Adjust angle of movement counter-clockwise: LEFT arrow key
Adjust angle of movement clockwise: RIGHT arrow key
Move forward: UP arrow key
Shoot missile: ENTER

Pressing LEFT or RIGHT also rotates the sprite.

I tried to code the game so that missiles will shoot from the "tank barrerl" (point marked in green). However, the code I wrote doesn't achieve this.

Instead, when pressing ENTER the missile appears in a point on the sprite or around it, that seems to be random.

(Orange point is the tank's origin: tank.getX(),tank.getY() ).

enter image description here

It wouldn't be a problem to code this, if it weren't for the fact the the tank rotates. The location of the green point changes everytime the user rotates the tank.

What is wrong with my code? This code should make the missile 'shoot' from wherever the "barrel" currently is. As I said, doesn't work.

This is what runs when the user presses ENTER.

enterAction = new AbstractAction(){
    public void actionPerformed(ActionEvent e){

        double missileXposition, missileYposition;
        double tankMiddleX,tankMiddleY;
        double angle, radius;

        tankMiddleX = tank1.getX() + (tank1.getWidth()/2);
        tankMiddleY = tank1.getY() + (tank1.getHeight()/2);

        angle = tank1.getAngle();
        radius = tank1.getWidth()/2;

        missileXposition = tankMiddleX + ( Math.cos(angle) * radius );
        missileYposition = tankMiddleY + ( Math.sin(angle) * radius );

        missiles1.add( new Missile( missileXposition, missileYposition , "red" , tank1.getAngle() , tank1) );

    }
};

The Missile class:

public class Missile extends Entity {

    public Missile(double x, double y, String type, double angle, Tank tank){

        this.x = x;
        this.y = y;
        this.dx = dx;
        this.dy = dy;
        this.type = type;
        this.angle = angle;

        if(type.equals("red")) image = new ImageIcon(this.getClass().getResource("sprites/redrocket1.png")).getImage();
        if(type.equals("blue")) image = new ImageIcon(this.getClass().getResource("sprites/bluerocket1.png")).getImage();

        width = image.getWidth(null);
        height = image.getHeight(null);

        if(type.equals("blue")) dx = (-1) * ( 6 * Math.cos(Math.toRadians(tank.getAngle())) );
        if(type.equals("red")) dx = 6 * Math.cos(Math.toRadians(tank.getAngle()));

        if(type.equals("blue"))  dy = (-1) * ( 6 * Math.sin(Math.toRadians(tank.getAngle()) ) );
        if(type.equals("red"))  dy = 6 * Math.sin(Math.toRadians(tank.getAngle()));

    }

}

Thanks a lot

Use String equals method instead of == for such comparisons type=="red" — Juned Ahsan
Note: Don't use == to compare String values. Use equals() — Alexis C.
You didn't change all == to .equals - there are still 4 ==s left — Njol

s3lph s3lph · Accepted Answer · 2014-01-04T15:17:21

Determine the distance between the sprite's origin (orange) and the missile start point (green) (d)and the angle between the upper rim of the sprite and the line orange-green a.

Now you set the start point of the missiles to

tank1.getX()+Math.cos(d*Math.toRadians(a+tank1.getAngle()));
tank1.getY()+Math.sin(d*Math.toRadians(a+tank1.getAngle()));

I don't know whether it's 100% correct, but I think it's the right direction.

Java 2D "tank" game: Shooting 'missile' from rotated sprite doesn't work

1 Answers