Question

Making a ship game because I am incredibly original.. With that aside, I have a problem. I have a function to fire bullets from my ship based on its rotation which works.. it uses this code on creation:

        var b = new Bullet  ;
        b.x = x;
        b.y = y;
        b.rotation = rotation;
        parent.addChild(b);
        bullets.push(b);
        score -=  50;
        trace(enemybullets[30].x + "," + enemybullets[30].y);

The above code is in my Ship class so I can easily make the bullets achieve the correct rotation.
And to continually update its position, in the bullet’s class:

        x += Math.cos(rotation / 180 * Math.PI) * speed;
        y += Math.sin(rotation / 180 * Math.PI) * speed;

So that all works well. But I have another class, EnemyBullet, which randomly generates and uses similar code to set its direction and movement. In my ship class:

        var eb = new EnemyBullet ;
        eb.x = (Math.random() * 550) - 550;
        //trace("eb.x is " + eb.x)
        eb.y = (Math.random() * 400) - 400;
        //trace("eb.y is " + eb.y);
        var a1 = eb.y - y;
        var b1 = eb.x - x;
        var radians1 = Math.atan2(a1,b1);
        var degrees1 = radians1 / Math.PI / 180;
        eb.rotation = degrees1;
        if (enemybullets.length < 50)
        {
            parent.addChild(eb);
            enemybullets.push(eb);
        }

And in the EnemyBullet class:

        x += Math.cos(rotation / 180 * Math.PI) * speed;
        y += Math.sin(rotation / 180 * Math.PI) * speed;

I have set up a trace to track where one of my bullets going, because they certainly aren’t appearing on my screen.. here are the results from my tracing:

x: 121.55, y:-162.05
x: 1197.05, y:-162.05
x: 1842.35, y:-162.05
x: 2368.15, y:-162.05
x: 2547.4, y:-162.05
x: 2702.75, y:-162.05
x: 2882, y:-162.05

I gather that the rotation is therefore always horizontal, but can’t for the life of me see why? Can anyone give me an answer? Assuming it’s simple enough because the code I used to setup the rotation is the same working code I have used to turn a movieclip towards the mouse..

Any ideas?

Ta!

Answer 1

The conversion from radians to degrees contains a bug:

var degrees1 = radians1 / Math.PI / 180;

Should be:

var degrees1 = radians1 / Math.PI * 180;

Or to make it more understandable:

var degrees1 = 180 * radians1 / Math.PI;

In your case degrees1 probably is value near 0; so movement is always horizontal.