如何避免与libgdx多次冲突？

Question

I'm coding my first 2D game using java and libgdx : a brick breaker.

I have some difficulties handling multiple collision.

Let met explain : I created an array of bricks (Brick extends Rectangle). All those bricks have the same parameters as rectangles but I added 4 booleans : left, right, up, down. When ball.y > brick.y --> up = true and all the others = false. And when up is true, if ball overlaps brick then ball.y *= -1. (for positions and speed, I'm using Vector2). It's exactly the same for the 3 others boolean (for left and right I use ball.x *=-1 of course).

if(briques.get(r).up_b == true || briques.get(r).down_b == true) {
            if(ball.overlaps(briques.get(r))) {
                vitb.y *= -1;   
            }
        }    

and

if(briques.get(r).left_b == true || briques.get(r).right_b == true) {
            if(ball.overlaps(briques.get(r))) {
                vitb.x *= -1;   
            }
        }

NB : vitb == ball speed (Vector2).

This part works perfectly. But here is the problem :

My ball have a width and height of 10 pixels. So, if all the bricks are at least 10 pixels far from each other it's ok. But if it's less, the ball can touch 2 brick at a time. And it just freezes then totally bugs...

I've tried so many things, I don't know what to do. I think it comes from the fact that 2 vectors are sending the ball in 2 different directions so I've tried this :

try {
        if(ball.overlaps(briques.get(r)) && ball.overlaps(briques.get(r+1))) {

            if(((posb.dst(posbr.get(r))) < (posb.dst(posbr.get(r+1)))) || ((posb.dst(posbr.get(r))) == (posb.dst(posbr.get(r+1))))){
                briques.get(r+1).up_b = false;
                briques.get(r+1).down_b = false;
                briques.get(r+1).right_b = false;
                briques.get(r+1).left_b = false;
            }
        }

        if(ball.overlaps(briques.get(r)) && ball.overlaps(briques.get(r + nb_br_par_ligne))) {
            if((posb.dst(posbr.get(r))) < (posb.dst(posbr.get(r+nb_br_par_ligne))) || (posb.dst(posbr.get(r))) == (posb.dst(posbr.get(r+nb_br_par_ligne)))){
                briques.get(r+nb_br_par_ligne).up_b = false;
                briques.get(r+nb_br_par_ligne).down_b = false;
                briques.get(r+nb_br_par_ligne).right_b = false;
                briques.get(r+nb_br_par_ligne).left_b = false;
            }
        }
        } catch(IndexOutOfBoundsException e){
            e.printStackTrace();
        } 

NB : posb == ball position // posbr == brick position // nb_br_par_ligne is the way to find the brick which is up or down "r" (nb_br_par_ligne = 13 here because I have 13 bricks per row).

In this code I have tried to say "If the ball touches 2 bricks, choose the nearest, if it's the same distance, then choose the one on the left. For the other one, set all booleans to false to avoid collision." I also added something to make bricks disappear only if it overlaps with ball AND if it's the brick that have been chosen, but it doesn't work.

I've also tried others things and I can't figure out what is wrong.

The two following samples works perfectly but I'm not sure I'm using them correctly with the mutliple collision : I tried to put them in the loop that tests if there is multiple collisions, then I tried to put it out of the loop...

if(ball.overlaps(briques.get(r))) {
            briques.get(r).setRes(briques.get(r).getRes()-1);

        }

if(briques.get(i).getRes() == 0) {
            briques.removeIndex(i);

        }

So I'm here to ask if someone can just give me an advice on how to avoid multiple collision if my ball touches 2 bricks.

Thanks all (and sorry if I made some mistakes with english).

Answer 1

You only need to change the velocity once.

Currently you change it two times, if the ball hits two bricks and x * -1 * -1 = x , which means you don't change it at all.

Just add a flag that the ball needs to change direction, which can only be set once per frame (or simulation step).

Then after the collision checks, check this flag (and reset it if necessary) and manipulate the velocity accordingly.

This flag could be an enum:

public enum Hit
{
     TOP, BOT, LEFT, RIGHT, NONE;
}

The default would be NONE so that you can check if the ball already hit something.