[Merged by Bors] - Expose transform propagate systems

[lewiszlw]

Objective

• I tried to create a fork of bevy_rapier to track latest bevy main branch. But bevy_rapier depends on bevy internal propagate_transforms system (see https://github.com/dimforge/bevy_rapier/blob/master/src/plugin/plugin.rs#L64).
• propagate_transforms system was changed to private in [Merged by Bors] - Parallelized transform propagation #4775.

I don't know if it's reasonable that making propagate_transforms public. I also created an issue to bevy_rapier dimforge/bevy_rapier#307 to see how offical team will solve this issue.

Solution

• make propagate_transforms system public.

[james7132]

You need to use both sync_simple_transforms and propagate_transforns for a full propagation. I don't like the idea of exposing them individually, and without the system labels. Could we make the plugin non-unique and allow it to be added with different system labels?

[alice-i-cecile]

Won't work unfortunately, since you can't yet control when plugin systems run.

[lewiszlw]

Could we make the plugin non-unique and allow it to be added with different system labels?

I'm trying to store stages in plugin like this,

pub struct TransformPlugin {
    stages: Vec<Box<dyn StageLabel>>
}
impl Default for TransformPlugin {
    fn default() -> Self {
        Self { stages: vec![Box::new(StartupStage::PostStartup), Box::new(CoreStage::PostUpdate)] }
    }
}

impl Plugin for TransformPlugin {
    fn build(&self, app: &mut App) {
        ...
        for stage in self.stages {
            app.add_system_to_stage(stage, systems::propagate_transforms.label(TransformSystem::TransformPropagate))
        }
    }

    fn is_unique(&self) -> bool {
        false
    }
}

There are two problems

1. Don't satisfy Plugin trait bound
2. Can't pass Box<dyn StageLabel> to add_system_to_stage method as param is impl StageLabel

What's your thought to allow plugin to be added with different system labels? @james7132

[mockersf]

You need to use both sync_simple_transforms and propagate_transforns for a full propagation. I don't like the idea of exposing them individually, and without the system labels.

Could we expose a single system that would run both? Not used in Bevy, just for external consumption for the case when someone wants to run global transform propagation when they want

[james7132]

Could we expose a single system that would run both? Not used in Bevy, just for external consumption for the case when someone wants to run global transform propagation when they want

We could just have a function that returns a SystemSet. That'd allow users to do what they want with it (add it to their own stages, label them however they wish, etc).

[mockersf]

Could we expose a single system that would run both? Not used in Bevy, just for external consumption for the case when someone wants to run global transform propagation when they want

We could just have a function that returns a SystemSet. That'd allow users to do what they want with it (add it to their own stages, label them however they wish, etc).

Sounds good! @lewiszlw could you add this function as public, and mention it in the docs or comments of propagate_transforms and sync_simple_transforms, and the docs of GlobalTransform (https://dev-docs.bevyengine.org/bevy/prelude/struct.GlobalTransform.html)?

[lewiszlw]

Sounds good! @lewiszlw could you add this function as public, and mention it in the docs or comments of propagate_transforms and sync_simple_transforms, and the docs of GlobalTransform (https://dev-docs.bevyengine.org/bevy/prelude/struct.GlobalTransform.html)?

Sure. I'm not very good at English, feel free to correct doc.

[alice-i-cecile]

Small corrections for the docs, then this looks good to me.

[alice-i-cecile]

bors r+

[bors]

Pull request successfully merged into main.

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