Sorry for not answering earlier in the other thread, but I was busy finished a JavaFX program for a contest, so I had no time to experiment... But I kept open your question to come back to it.

Anyway, it was a good idea to open a new thread, no only for visibility but also to avoid "polluting" threads with questions unrelated to original topic... :-D

I haven't tried yet contact listener, but of course it is on my (virtual) todo list. I will do as I did for the mouse joint, I will experiment and integrate latter in the tutorials... Meanwhile, if you have a handy link to existing code, it might save me some researches.

Hiya,

Im developing a game which you can see here:
http://blissfulthinking.nl/gamezero

It uses processing as well as jbox2d just like yours.

I would like to share my solutions but I think they are hard to use if you stick with the processing .pde editor.  Its really easy to use both processing and jbox2d from the Eclipse programming environment.
[EDIT: Excuse me if im wrong, but I am under the assuption you use the .pde editor, ok byebey]

http://www.eclipse.org/
If you want I can send you links to my project files.

My solution is one where ContactPoints are collected each frame and than reviewed in between. My CustomWorld class looks at them to see if both bodies have custom data (i.e. the getUserData thing) attached. If they both do object A is sent to object B and vice versa.

All attached userdata shares the same parent class called WorldObject. But the children of this class (which extend this class) all inherit different Interfaces that show which contacts are relevant to it.

For instance, the player object is interested in enemy bullets and the enemy ships are interested in player bullets etc. I call these Filters in my implementation but they should not be confused with the Filters that come with JBox2D (which I didn't use so far).

Let me know if you want to see the code!

N.B. I also maintain a thread with some of my algorithms here but those are not contact point related, they are about doing raycasts on polygons and stuff
http://www.box2d.org/forum/viewtopic.php?f=9&t=3411

Finally, I get it work! (pfuiii).
But, I had to learn a lot of new things. I moved everything into eclipse (not so easy, but the IDE is really great to work with).
Then I used exactly what is explained at http://www.kerp.net/box2d/ (see the 2 links above). With a few modifications, it's not too complicated to translate it from AS3 to Java.
I'm quite sure my code is the ugliest you could find, so, I'm not sure it would be interesting to post it.
We are far away from the beautiful simplicity of Processing and Boxwrap2d…
Thanks for your help, PhiLho and Michiel.
Gui-aum

I summerized my method in a document at http://blissfulthinking.nl/jbox2dguide_collisions.pdf

For those of you who are realising that none of the other examples are in Processing, or wishing gui-aum had posted his solution, here is a working method:

Code:

public class CustomListener implements ContactListener {
  CustomListener(){
  };
  void add(ContactPoint cpoint)
  {//contacts collide for the first time
    println("new hit");
  }

  void persist(ContactPoint cpoint)
  {//contacts continue to collide - i.e. resting on each other
  }

  void remove(ContactPoint cpoint)
  {//objects stop touching each other
  }

  void result(ContactResult point)
  {//coltact point is resolved into an add, persist etc
  }
}
 

then you have to add the custom listener to your world
Code:

    m_world = physics.getWorld();
    m_world.setContactListener(new CustomListener());
 

Hope that's useful.

You have to add also the given CustomListener class, with stuff within.

And BoxWrap2D doesn't wrap all JBox2D, so the latter must be checked for advanced stuff.