I whipped up a distance based collision detection system, dubbed Disc Collision. A very basic model for collision detection, but also very fast in comparison to the vector based hitTest() in the Flash API.
Collisions are detected by a request-only model. The collision detection simply manages a collection of points and distances associated with each point. So you could easily put this into your a game engine and run an update call to get colliding points.
The algorithm is robust and has a few things to optimize. The collection of points is subdivided into multiple lists according to a spatial grid. To reduce the amount of work required detection. Then all of our points are sorted through a BST by distance so that we always know the largest distance to use when selecting grid sections.
Hold the red button down below to create objects to test collisions.
You can get code here:
http://code.google.com/p/disccollision/
https://github.com/henrytseng/disccollision
