Get collision event forces?

[tversteeg]

Is it possible to get any extra information when a collision occurs, such as the impact force? When I print an event using EventReader<CollisionEvent> I just get the following information:

event = Started(
    CollisionData {
        rigid_body_entity: 8v0,
        collision_shape_entity: 8v0,
        collision_layers: CollisionLayers {
            groups: 4294967295,
            masks: 4294967295,
        },
    },
    CollisionData {
        rigid_body_entity: 19v0,
        collision_shape_entity: 19v0,
        collision_layers: CollisionLayers {
            groups: 4294967295,
            masks: 4294967295,
        },
    },
)

I would like to see with how much force the two objects collided. I tried looking into the attached collider entities, but these don't have this kind of information.

[jcornaz]

Mmh, interesting requirement.

I don't see how to provide such information. The event we get from rapier only contains a reference to the collider (which in turns has a reference to the rigid body): https://docs.rs/rapier3d/latest/rapier3d/geometry/enum.ContactEvent.html

And I don't think we can get information about the collision from either the collider or rigid body.

[tversteeg]

Thanks for the reply. For now I'm using the velocity of the object since most collisions are against static objects, but it's not really ideal.

[jcornaz]

Yes of course, this isn't ideal.

After searching more, we may be able to extract the ContactData from rapier's contact graph. Which contains the impulse info.