Dealing with collisions across adjacent static bodies

Question

The Problem:

I have the following setup:

A, B and C are rectangular static bodies in box2d. p is a circular dynamic body in box2d.

The movement of 'p' is solely controlled by the current gravity force of the world.

When 'p' collides with a static body (A, B or C) I play a bouncy sound. I handle this through a standard ContactListener. No problems there.

The problem arises when 'p' is on 'A' and traveling left towards 'B'. This causes another collision to fire (on 'B') which results in another bouncy sound which is unwanted. If however 'p' was to be traveling right and contacted 'C' I would want the sound to play (given enough velocity, etc).

TL;DR - When sliding across multiple static bodies how do I effectively ignore collisions from a body that is on the same 'line' I'm already on?

What I've Tried:

I've tried numerous different approaches such as on collision tracking that normal as my 'ground' normal and ignoring collisions from the same normal. This works until I do something like make contact with 'C' which then becomes my new 'ground' normal. But having never lost contact with 'A' if I go back towards 'B' I will trigger another collision and we're back to square one.

The Plea:

Looking for code-based solutions or ideas if at all possible. I've considered trying something like a chain shape around my level's collidable areas, but with certain parts of my world being dynamic I don't feel like that's an adequate solution.

Thanks!

Answer 1

If I understand the problem correctly, you were close to properly solving it.

Your approach with the normals is what you want, but instead of only saving the normal of the last collision, save a list of normals from all current collisions/overlappings. Then, play the sound whenever the new normal of the new collision is not yet present in the list.

In further detail, a "pseudo-implementation" would be like the following (to be applied regarding each obstacle with which collision happens/stops happening):

Vec2<> normals_list; //create a list to hold the normals
OnCollisionEnter(){
    Vec2 col_normal = Get.Collision.normal; //get the normal of the new collision
    int presence_in_list = 0;
    for(i=0; i < normals_list.Length; i++)
    {
        if(col_normal  == normals_list[i]){ presence_in_list; += 1; } //check how many times current collision's normal is already present within the list
    }
    if(presence_in_list == 0) { play.sound; } //if not present, play the sound
    normals_list.Add(col_normal); //add the normal of current collision to the list
}

OnCollisionExit{
    Vec2 col_normal = Get.Collision.normal; //get the normal of the new collision
    for(i=0; i < normals_list.Length; i++)
    {
        if(col_normal  == normals_list[i]){
            normals_list.Remove(normals_list[i]); //remove the normal from the list
            col_normal = Vec2(0,0); //to avoid deleting more than once, in case there were repeated normals in the list
        }
    }
}

Answer 2

Have you considered playing the sound when the direction of the ball changes? Or like add that as a condition, in addition to the already "collide with object" condition.

Answer 3

Ok, I'm piggy-backing on Skitskraj's answer here so if you like mine, upvote his/hers too.

Solution: Play the sound only if there is a new contact and there is a significant velocity change. I would suggest using the postSolve callback on the first iteration of the collision to determine if the impulse is above some threshold value required to generate the bouncing sound.

Answer 4

Since you're not strictely looking for code-based answers you might want to try:

Of course assuming it doesn't constrict your level design. (Skitskraj's answer is pretty good too tho)