Rework AsyncCollider and add AsyncSceneCollider

[Shatur]

Closes #144.

I turned AsyncCollider into a struct and moved collision shape into a separate enum to reuse it for AsyncSceneCollider. This also allows to check if mesh is loaded without expanding the enum.

Maybe we should replace bevy_mesh, bevy_mesh_convex_decomposition and bevy_mesh_convex_decomposition_with_params with a single function which accepts AsyncColliderShape (if yes, how would you will rename it)?
This will make things more clear and allow to get rid of matches in init_asyc_* systems.

[Shatur]

I also think we probably should use Option<AsyncColliderShape> so that the user can specify None for shapes to skip.

[sebcrozet]

Maybe we should replace bevy_mesh, bevy_mesh_convex_decomposition and bevy_mesh_convex_decomposition_with_params with a single function which accepts AsyncColliderShape (if yes, how would you will rename it)?

Yeah, that would be more ergonomic. Though in that case, the name AsyncColliderShape doesn’t fit very well because the computation is carried out immediately. Perhaps we could rename it ComputedColliderShape? And then we could rename bevy_mesh to from_bevy_mesh.

I also think we probably should use Option so that the user can specify None for shapes to skip.

Good idea.

[Shatur]

@sebcrozet done!

[sebcrozet]

Thank you for this PR! It looks nice. All mentions of "recursive children" should be replaced by descendant since that’s what they are called in a tree-like data structure.

This doesn’t handle changes of Transform properly when a collider if down the hierarchy. But fixing this can be considered out of the scope of this PR.

[sebcrozet]

Instead of building a LinkedList with all the descendants, I think it would be more efficient and versatile to replace get_children_recursively by a traverse_descendants function that would look like this:

fn traverse_descendants(entity: Entity, children: &Query<&Children>, f: &mut impl FnMut(Entity)) {
    if let Ok(entity_children) = children.get(entity) {
        for child in entity_children.iter() {
            f(child);

            let mut children = get_children_recursively(*child, children);
            all_children.append(&mut children, f);
        }
    }
}

So this for child in get_children_recursively(entity, &children) would simply call traverse_descendants and provide a closure.

[sebcrozet]

As far as I know the SAFETY comments are for unsafe blocks instead of unwraps.

Suggested change

	let mesh = meshes.get(handle).unwrap(); // SAFETY: Mesh is already loaded
	let mesh = meshes.get(handle).unwrap(); // NOTE: Mesh is already loaded

[sebcrozet]

Let’s just print an error instead of panicking, and specify the name of the mesh that failed:

Suggested change

	None => panic!("Unable to generate collider from mesh"),
	None => error!("AsyncSceneCollider: unable to generate collider from mesh `{}`", name),

[Shatur]

Thanks! Applied the suggestions and fixed conflicts in changelog with the latest master.
I made error messages without AsyncSceneCollider: for consistency with other error messages in this crate. But feel free to let me know if I should change it.

[sebcrozet]

Looks great, thanks!