Contents
When do you call collision function in Box2D?
Collisions between entities in the world will be detected during the b2World::Step () function that we call every time step. As we saw in the topic on worlds , the b2World::Step function advances the simulation, moving all the bodies around and so on.
How to get b2contact objects from Box2D?
There are two main ways you can get these b2Contact objects from Box2D. One is to look at the current list of contacts for each body, and the other is to use a contact listener.
How to tell Box2D when the contact state changes?
Now, we want Box2D to tell us when the contact state changes. Make a subclass of b2ContactListener and implement the BeginContact/EndContact functions as follows: That seems like a lot of code but if you take a look it’s mostly just repeated. First we check if the body of the fixture has any user data.
How does a rigid body work in Box2D?
Bodies are always rigid bodies in Box2D. That means that two fixtures attached to the same rigid body never move relative to each other and fixtures attached to the same body don’t collide. Fixtures have collision geometry and density. Normally, bodies acquire their mass properties from the fixtures.
How to check if collision callbacks are correct?
Adding a whole bunch of balls and bashing them around can be a good way to check if you’ve got this right. Notice that when things are in a pile bouncing around, the contact state can flicker on and off at a very quick rate. There’s nothing wrong with that, but if you are running game logic from these state changes, keep this in mind.
What happens when Box2D collides two shapes?
But normally when Box2D collides two shapes, it views them in isolation. Fortunately, the edge shape provides a mechanism for eliminating ghost collisions by storing the adjacent ghost vertices. Box2D uses these ghost vertices to prevent internal collisions.
Why do I get Ghost collisions in Box2D?
These ghost collisions are caused when the polygon collides with an internal vertex generating an internal collision normal. If edge1 did not exist this collision would seem fine. With edge1 present, the internal collision seems like a bug. But normally when Box2D collides two shapes, it views them in isolation.
Why are edge shapes not used in Box2D?
A major limitation of edge shapes is that they can collide with circles and polygons but not with themselves. The collision algorithms used by Box2D require that at least one of two colliding shapes have volume. Edge shapes have no volume, so edge-edge collision is not possible.