Allow tweaking low-level RigidBodyBuilder

[MOZGIII]

I'd like a capability to tweak RigidBodyBuilder's parameters at rigid body spawn time in an arbitrary manner.

My concrete interest for now is turning on ccd_enabled - but something else might be required later (I can imagine sleeping and related stuff).

[jcornaz]

Hi,

For each of theses needs, I would rather improve heron to add a dedicated component to the API (but only when actually needed). So for your current need we could feature a ContinuousCollisionDetection component. And we may add a Sleeping component when the need will arise for someone.

I understand it means that heron's is more limited, as one has to wait until heron adds support for each feature.

But it is somewhat the point of this plugin. Users that want full power of rapier out-of-the box (at the cost of higher complexity) can use bevy_rapier, and the point of having heron as an alternative, is to provide a well-crafted data-oriented API (at the cost of being more limited).

[jcornaz]

Yes of course I understand that.

The point of the readme you are referring to, is something that I would like to uphold. However, it is not the case atm.

But I have an Idea on how to make it true.

I cannot expand much on it right now, but I hope to be able to give more details, and maybe even implement a solution today or tomorrow.

[jcornaz]

Mmh, actualy it should be already possible. Not well documented, nor nice, but possible.

You can create the rigid-body using RigidBodyBuilder and add the rigid body yourself to the RigidBodySet resource. Then you insert the handle returned by the RigidBodySet as a component alongs others heron components.

That way heron should recognise the rigid body and still manage it.

[MOZGIII]

I don't want to take over the complete creation of the RigidBodyBuilder though, just want to toggle a boolean.

This could be done by allowing some kind of hook: fn myfn(rigid_body_builder: &mut RigidBodyBuilder).

If there were a resource that would allow such tweaking - I'd be happy.

That said - maybe the hook as described above is not the best API for the long term... So I'd do a couple more passes on this.

Maybe we can have a hook like this at a component level - so it's applied per archetype? Might be worth exploring...

[jcornaz]

If you want heron events to work when using this techinque, you have to write the bevy entity (as bits) in the rigid-body data.

[jcornaz]

I don't want to take over the complete creation of the RigidBodyBuilder though, just want to toggle a boolean.

This could be done by allowing some kind of hook: fn myfn(rigid_body_builder: &mut RigidBodyBuilder).

If there were a resource that would allow such tweaking - I'd be happy.

That said - maybe the hook as described above is not the best API for the long term... So I'd do a couple more passes on this.

Maybe we can have a hook like this at a component level - so it's applied per archetype? Might be worth exploring...

Yeah, maybe. But it would be a shame to spend too much time on desiging and implementing this instead of directly adding first-class support for a ContinuousCollisionDetection component.

[apastushenka]

I don't want to take over the complete creation of the RigidBodyBuilder though, just want to toggle a boolean.

You can use code like this for adjusting a rigid body after creation:

use heron::rapier_plugin::rapier2d::dynamics::{RigidBodyHandle, RigidBodySet};

struct EnableCcd;

fn adjust_rigid_body(
    mut commands: Commands,
    mut bodies: ResMut<RigidBodySet>,
    handles: Query<(Entity, &RigidBodyHandle), With<EnableCcd>>,
) {
    for (entity, handle) in handles.iter() {
        if let Some(body) = bodies.get_mut(*handle) {
            body.enable_ccd(true);
            commands.entity(entity).remove::<EnableCcd>();

            println!("{:?}: enable ccd", entity);
        }
    }
}

But there is a pitfall (correct me if I'm wrong): according to functions remove_invalids_after_component_changed and remove_invalids_after_components_removed in body.rs heron removes and creates again a rapier::RigidBody after RigidBody/RotationConstraints/PhysicMaterial component changed or removed, so your low-level settings of a rigid body will be lost in this case.