Instance-Generic Collision Detection in Actionscript

Question

I've tried using hitTestObject(), but that seems to require that I make the call using a specific instance, rendering it more or less useless unless I want to have dozens of objects making dozens of collision checks each frame, which just seems wasteful and annoying to implement.

Is there any way to do collision check based on class rather than instance?

Maybe Something equivalent to this: http://docs.yoyogames.com/source/dadiospice/002_reference/movement%20and%20collisions/collisions/place_meeting.html

Alternatively, is there any function that returns whatever a list of objects that share overlapping coordinates with the one I'm checking?

Joe Borysko · Accepted Answer · 2015-04-12 23:49:49Z

1

If I'm understanding your question correctly, you have several objects of that same class that each need to check for collisions against each other?

Yes, you would have to go through each object and perform a collision check against the other objects. I suppose you could write a hitTestClass function yourself, but behind the scenes it would still be the same. As far as implementing it, it's not so bad:

for( var i:int = 0; i < asteroids.length -1; ++i )
{
    var a:Asteroid = asteroids[ i ];
    for( var j:int = i+1; j < asteroids.length; ++j )
    {
        var b:Asteroid = asteroids[ j ];
        var isColliding:Boolean = a.hitTestObject( b );
        //Code here to do whatever in the case of collision
    }
}

If computational speed becomes a concern, then there are broad-phase collision detection techniques to chunk down the time. Quad trees are one example.

answered Apr 12, 2015 at 23:49

Joe Borysko

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5 Comments

Marty Over a year ago

I am confused about the ranges you're iterating over; why does j begin at i + 1? Your code could be simplified to something like this.

Joe Borysko Over a year ago

@Marty It prevents from unnecessarily checking each pair of objects twice. If there's an array of 3 objects, {a,b,c}, then with the loops in my answer, a-b, a-c, b-c is the checking order. If you do the two foreach loops with your example, a-b, a-c, b-a, b-c is the checking order.

SilentDrew Over a year ago

Well the main problems is that it evaluates at O(n^2), which is fine for small numbers of objects, but as I said I'm planning to use dozens of objects, so it's just not a viable solution

Joe Borysko Over a year ago

en.wikipedia.org/wiki/Quadtree will help you then. Collision detection's a deep topic...

Joe Borysko Over a year ago

Box2D is a 2D physics library for Flash if you want to go that route.

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