Collision Detection of Sprites in Actionscript 3.0 Flash

Question

I am making an achtung die kurve-like game in AS3.0. So far I've done the movements of the 4 different players, and it works alright.

I am now to make collision detection, in order to test if a 'worm'-so to speak, is colliding with eachother or its own tail.

As I understand it, if I use hitTestObject(); it will use the registration area of the whole object, which would be a huge problem, seeing since this registration makes a 4-sided registration that contains all of the object. So if this is used, it will 'collide' just by entering this rectangle instead of hitting the actual worm. Is this correctly understood?

I've been looking through different methods of collision detection, and can't seem to find an optimal one for my project.

My thought were to check if the 'worms' are drawing their new sprites on a white background. if they aren't, then it must have hit something.

You can see how I used my code here: code in .as format linked to an .fla file

Sorry for my ill-formulated question, hope it makes somewhat sense. Any help is greatly appreciated!!

Best regards - Jesper

Answer 1

Try this function if you want a Pixel Perfect Collision Detection with efficient CPU usage:

trace("Collided: " + (areaOfCollision(mc1, mc2) != null));
trace("Where: " + areaOfCollision(mc1, mc2));

function areaOfCollision(object1:DisplayObject, object2:DisplayObject, tolerance:int = 255):Rectangle {
    if (object1.hitTestObject(object2)) {
        var limits1:Rectangle = object1.getBounds(object1.parent);
        var limits2:Rectangle = object2.getBounds(object2.parent);
        var limits:Rectangle = limits1.intersection(limits2);
        limits.x = Math.floor(limits.x);
        limits.y = Math.floor(limits.y);
        limits.width = Math.ceil(limits.width);
        limits.height = Math.ceil(limits.height);
        if (limits.width < 1 || limits.height < 1) return null;

        var image:BitmapData = new BitmapData(limits.width, limits.height, false);
        var matrix:Matrix = object1.transform.concatenatedMatrix;
        matrix.translate(-limits.left, -limits.top);
        image.draw(object1, matrix, new ColorTransform(1, 1, 1, 1, 255, -255, -255, tolerance));
        matrix = object2.transform.concatenatedMatrix;
        matrix.translate(-limits.left, -limits.top);
        image.draw(object2, matrix, new ColorTransform(1, 1, 1, 1, 255, 255, 255, tolerance), BlendMode.DIFFERENCE);

        var intersection:Rectangle = image.getColorBoundsRect(0xFFFFFFFF, 0xFF00FFFF);
        if (intersection.width == 0) return null;
        intersection.offset(limits.left, limits.top);
        return intersection;
    }
    return null;
}

After a successful preliminary hitTestObject(), this function backgroundly takes a snapshot from the shapes of both objects painted with different colors each, then overlays them intersecting the colors on a new one, returning the Rectangle of the resulting shape. So cool.

To learn more about Pixel Perfect Collision Detection you can google Collision Detection followed by one of these names: "The ActionScript Man", "Troy Gilbert", "Boulevart (wim)", "Grant Skinner (gSkinner)" or "Senocular". Those guys are awesome AS3 references by the way.