Fix collision detection by calculating positive penetration depth.

[ak-1]

I had an issue with collision detection not working properly. Changing in collide_aabb the calculation of the penetration depth (making it a positive value) fixed it for me.

[ak-1]

To reproduce the issue play breakout with the following change applied:

--- a/examples/game/breakout.rs
+++ b/examples/game/breakout.rs
@@ -59,7 +59,7 @@ fn setup(
         .spawn(SpriteBundle {
             material: materials.add(Color::rgb(1.0, 0.5, 0.5).into()),
             transform: Transform::from_translation(Vec3::new(0.0, -50.0, 1.0)),
-            sprite: Sprite::new(Vec2::new(30.0, 30.0)),
+            sprite: Sprite::new(Vec2::new(100.0, 100.0)),
             ..Default::default()
         })
         .with(Ball {

Here is a demo: https://ibb.co/bHr8LHq

[cart]

The fix in this pr definitely solves the issue in question. I can reproduce the error shown in the video and the pr resolves it, but I think flipping the sign just shifts the problem elsewhere (in a way that is more favorable for the breakout example). I think the core issue is that the penetration depth is a signed comparison, when it should really be absolute.

Applying this change instead both resolves the bug in the demo video and resolves a bunch of other collision jank. Can we adjust this pr to do that instead?

[ak-1]

Looks good to me. I wanted to update this PR but closed it accidentaly and was not able to re-open it. #966 is the followup.