AS3 Predictive collisions (Sweep testing)

Question

I'm making a basic platformer engine in AS3, and I'm currently implementing gravity. The gravity currently lets the player sink a few pixels into the ground when it lands (depending on the player's speed), and I don't want that.

I want to be able to test collisions 1 frame ahead of time (sweep testing), and if a collision will happen in the next frame, I want the player to stop 0px into the ground, regardless of the player's speed.

I also want pixel-perfect collisions that take the shape of the terrain, so I've been using Corey O'Neil's Collision Detection Kit (CDK), which works very well for detecting collisions, but I can't work out how to make it predict them. I'm not sure if this is the best library to use.

I'm not sure about Box2D; I feel it's too much for what I want.

Any idea of how can I do pixel-perfect sweep tests in AS3?

Answer 1

Box2D should be pretty good for small projects as well, also in case if you wish to scale up later...

If you need quicker dive in, have a look at Quick Box 2d.

There are couple of good tutorials (here & here) as well.

Answer 2

^{I want to be able to test collisions 1 frame ahead of time (sweep testing), and if a collision will happen in the next frame, I want the player to stop 0px into the ground, regardless of the player's speed.}

In you game loop, where you are checking the colisions, just add the movement that will be done in the next frame, the current Y speed. Something like this:

if(currentYSpeed + player.y >= ground.y)
{
    player.y = ground.y
}else
{
    player.y += currentYSpeed;
}