Box2D Forums

Hello. I have posted this elsewhere but I haven't had any feedback from this. I was hoping posting here to the Box2d experts may provide greater enlightenment

I am using a contact listener to work out when two fixtures collide. This is working as expected.

What I am attempting to do is flag up if three objects collide. An example of this would be only flag a collision if three tiles are touching each other in some sort of 'chain'. I am unsure the best way of doing this and wanted to ask if there is already a standard approach.

Is it possible to simply check if an object is touching anything else? I have looked through the API but can't seem to find anything. If this is possible I could recursively loop through each of the 'collided/connected' objects and notice a three point collision if I end up recursing through three objects.

Thank you

As well as the contact listener which tells you when contacts start and end, you can get a list of the current contacts for each body at any time with GetContactList to do something like what you are talking about. Just remember to also check that the contact really IsTouching.
Check the section "9.3 Accessing Contacts" in the manual, this page might be helpful too:
http://www.iforce2d.net/b2dtut/collision-anatomy

This was a great help. Thank you. I wrote a recursive method that loops through each of the collided bodies until it found one with three touching parts.