Collision and bounce detection from array of points

I have an array of points that I will use to generate a closed po开发者_如何学JAVAlygonal fence on the outside of a game stage (2D). I wish to have collision detection between this fence and a bouncing ball-like object on the inside.

Additionally, I would like to be able to arbitrarily add/remove/redraw the fence in realtime and have the collision detection still operate realistically.

I have considered drawing a Sprite/Shape from the points and doing a HitTest at each frame to check whether to bounce or not.

My question: is this the best/correct way to accomplish this goal? Consider something like JezzBall with diagonal lines of any angle a simulation of what I'm trying to do.

Check the corners of your bouncing ball with four hitTestPoints. If it succeeds, then do hitTestPoints from the fence with shapeflag set to true.

There may be better solutions as I do not know the performance impact of shapeflag, but combined with the corners optimization I think it will be good, but I'm also interested if there is a better way.

Math will be your friend here. Do a quick search for circle-line, or point-line collision (here's one: Circle line-segment collision detection algorithm?).

What you do is run through your array of points, creating lines. So line 1 will be points[0] and points[1], and line 2 will be points[1] and points[2]. After that you check each line against your ball (if you want proper collision that will work no matter the frame rate, then you create a ball line, which is the line that the ball has travelled along between the last frame and this one). Do your collision detection against the ball line and each line made from your points (there's tons of line-line collision detection algos on the web). What you'll get out of an algorithm like that is the time the collision takes place in the current time step, as well as the normal of the colliding line, which will give you the reflection angle.

If you don't know Vector math, then learn it, it'll make your life a ton easier. Again, there are tons of implementations of a Vector2 class on the net.

You can arbitrarily remove parts of the wall as needed by just ignoring those points in your check.

Another lazy solution would be to use a physics engine like Box2D http://box2dflash.sourceforge.net/ or Nape: http://code.google.com/p/nape/ - it might be overkill for what you want for your game, but hey, it's easy.

For bonus points, another technique which might be easier for you is the Separating Axis Theorem, which is used in the flash game N: http://www.metanetsoftware.com/technique.html