How can I get coordinates of object collision in AS3?

Question

I'm trying to write a simple flash game like Space Invaders. When the ship shoots I check if bullet hits the enemy with simple if like below:

if (bullet.hitTestObject(enemy)) {
var explosion = new Explosion(enemy.x, enemy.y);
stage.addChild(explosion);
explosions.push(explosion);
//Rest of logic like removing bullet and enemy from stage
}

What I expected to see was an Explosion instance appearing somewhere around the coords where bullet hit the enemy and that it would stay in place. Instead explosion seems to be appearing completely elsewhere and is moving in the same direction the enemy was (opposite direction to bullet). It seems that my assumption about successfully getting coordinates in a way presented above isn't right. Is there any other way to get it at least approximately? It doesn't have to be pixel-perfect, but I don't want explosion to appear on the other side of the stage.

Thanks for any suggestions.

Andrey Popov Andrey Popov · Accepted Answer · 2014-06-03T13:09:22

It's not about getting the coordinates but having in mind where your children are added.

If the container is moved around, and you add the explosion to other container, the coordinates will mess up - each object has an internal coordinate system starting from 0,0.

Best advise would be to manually understand where's the difference and where are your children added. Common way to fix this is to add all your children at 0,0. This will give you full control and nevertheless an idea of how Flash works.

If you are unable to do so, you can always use globalToLocal and localToGlobal methods that will help you convert those coordinates to a global (Stage) ones, and vise versa.

How can I get coordinates of object collision in AS3?

1 Answers