Question

This is something I’m trying to do for a university assignment and I’m quite new to it, but I’ve done a lot of reading on the subject. Please could someone to explain, in the simplest terms, how to do what I’m trying to do, so that I can understand what needs to happen?

I have an array of objects, each draw a circle to the screen; I have them bouncing within a bounding box but now I’d like them to collide.

I wrote the method below, which is working… but only just. The balls occasionally get stuck and ‘jitter’ on one another and I have no idea why this is happening. Also, I think I’m checking for more collisions than necessary(?).

void handleObjectCollision() {

for(int i = 0; i < _myBtns.length; i++) {

 if(i != _id) {

    float dx = _myBtns[i].x - x;
    float dy = _myBtns[i].y - y;
    float distance = sqrt(dx*dx + dy*dy);

    if(distance < r * 2) {
      xS = -xS;
      yS = -yS;

      // Debug
      // println("Collision!");
    }

  }

}

A full paste of my class and pertaining segments can be found here: http://pastebin.com/eJawiHAE.

Also, here is an example I’ve been working from, http://processing.org/learning/topics/bouncybubbles.html.

I’m trying to achieve a simple bounce (reversal in speed?), without added physics or using vectors, as I want to be able to understand what’s happening in it’s simplest form, first.

Thank you.

Answer 1

You cannot just reverse the direction in which your object is moving, because the collision may happen almost from behind it, in which case the reversal will put it again in collision course against the object which collided with it. That explains the jitter that you see. You need to consider the direction from which the collision occurred, and adjust your direction vector accordingly, using the related physics formulas for what is known in physics as “elastic collisions”.

Here, check this out: http://en.wikipedia.org/wiki/Elastic_collision