Box2D Forums

Is it possible to get the normal of each edge for a Contact List of a colliding dynamic body????

There is no standard method provided to get that. Contacts only have a normal vector showing the quickest way for the two fixtures to be pushed apart, because that is the goal of the collision response.

At least, that would be my answer if I understand your question correctly, but it's not quite clear what you mean... for example in the case below, what is the answer?

Well, in that case, we would get more than one contact point (maybe two) from body->GetContactList(), each contact pertinent to a different edge. I Would like to get the normal vector of each one of those edges.. then find know its orientation and do a calcle to find which faces of our body are colliding.

I thought contact->manifold->localNormal was going to be this normal, but it is not... localNormal from the manifold of a contact doesn't give me the right information, and I dont know how to find the edge's vertex and be able to calcle its normal.

Finding the current position of the vertices can be done like http://www.iforce2d.net/b2dtut/gotchas#getfixturepoints , and then the normal will be just the perpendicular line to each edge. But the real problem is knowing which edges to do this for, and unfortunately I think you are on your own there. You might be able to get some tips from the file b2CollidePolygon.cpp because Box2D needs to do some very similar computation, but it also takes some shortcuts because it doesn't need all the information you are looking for.

I see... nah, we will used those sensor fixtures for collision sides, it is working quite well but i was wondering if the older method could be done here.

Thanks for all!
P.S: As soon as the game is finished i'll post it somewhere in the forum!!