set_position has no effect on collider after calling step

[eldyer]

To demonstrate the issue I made the following test, which should be self-explaining.
Notice the use of position in the collider description builder vs. set_position.

#[test]
pub fn test() {
    use nalgebra::{Isometry3, Vector3};
    use ncollide3d::shape::{Cuboid, ShapeHandle};
    use nphysics3d::{
        force_generator::DefaultForceGeneratorSet,
        joint::DefaultJointConstraintSet,
        object::{BodyPartHandle, ColliderDesc, DefaultBodySet, DefaultColliderSet, Ground},
        world::{DefaultGeometricalWorld, DefaultMechanicalWorld},
    };

    // world
    let mut mechanical_world = DefaultMechanicalWorld::new(Vector3::new(0.0, -9.81, 0.0));
    let mut geometrical_world = DefaultGeometricalWorld::<f32>::new();
    let mut bodies = DefaultBodySet::<f32>::new();
    let mut colliders = DefaultColliderSet::new();
    let mut joint_constraints = DefaultJointConstraintSet::<f32>::new();
    let mut force_generators = DefaultForceGeneratorSet::<f32>::new();

    // ground
    let ground_thickness = 0.2;
    let ground_shape = ShapeHandle::new(Cuboid::new(Vector3::new(3.0, ground_thickness, 3.0)));

    let ground_handle = bodies.insert(Ground::new());
    let co = ColliderDesc::new(ground_shape)
        .translation(Vector3::y() * -ground_thickness)
        .build(BodyPartHandle(ground_handle, 0));
    colliders.insert(co);

    let cuboid = ShapeHandle::new(Cuboid::new(Vector3::repeat(0.2)));
    let isometry = Isometry3::translation(1.0, 1.0, 1.0);

    // collider 1
    let co_1 = ColliderDesc::new(cuboid.clone())
        .position(Isometry3::translation(1.0, 1.0, 1.0))
        .build(BodyPartHandle(ground_handle, 0));
    let co_handle_1 = colliders.insert(co_1);

    assert_eq!(colliders.get(co_handle_1).unwrap().position(), &isometry);

    // collider 2
    let mut co_2 = ColliderDesc::new(cuboid.clone()).build(BodyPartHandle(ground_handle, 0));
    co_2.set_position(Isometry3::translation(1.0, 1.0, 1.0));
    let co_handle_2 = colliders.insert(co_2);

    assert_eq!(colliders.get(co_handle_2).unwrap().position(), &isometry);

    mechanical_world.step(
        &mut geometrical_world,
        &mut bodies,
        &mut colliders,
        &mut joint_constraints,
        &mut force_generators,
    );

    // passes
    assert_eq!(colliders.get(co_handle_1).unwrap().position(), &isometry);

    // fails!
    assert_eq!(colliders.get(co_handle_2).unwrap().position(), &isometry);
}

[sebcrozet]

Hi!

This is expected. We should probably make set_position not callable from outside of nphysics itself. The position of a collider is recomputed automatically at each timestep, using the position of the body it is attached to, and the collider position relative to the body (given by collider.position_wrt_body). Perhaps we should add a collider.set_position_wrt_body method instead.

[jaredly]

Oh hey I just ran into this :D I would love a set_position_wrt_body!