Is it possible to manually get SystemParam to call non system functions?

[Bastczuak]

Hello,

is it possible in bevy_ecs to get a SystemParam manually from a world? I'm asking because I use opengl which is a c_void pointer and can't be used for bevys system because of missing send + sync. I give you an example.

main() {
  ...
  gameloop {
    ...
    schedule.run(&mut world);
    // call a function manually to render after world run
    render(&gl, world.get_system_param::<RenderData>()
  }
}

#[derive(SystemParam)]
struct RenderData<'w, 's> {
  camera: Res<'w, Camera>,
  transforms : Query<'w, 's, &'static Transforms>,
}

// not a registered system
pub fn render(opengl: &Gl, render_data: Renderdata) {...}

[alice-i-cecile]

Does SystemState do what you need?

[Bastczuak]

Yes that did the trick! Thanks!

type RenderSystemState<'w, 's> =(
  Res<'w, Camera>,
  Query<'w, 's, &'static Transform>,
);

main() {
  ...
  let mut render_state = SystemState::<RenderSystemState>::new(&mut world);
  ...
  gameloop {
    ..
    schedule.run(&mut world);
    render(&gl, render_state.get_mut(&mut world));
  }
}

pub fn render(opengl: &Gl, render_state: RenderSystemState) {
    let (camera, query) = render_state;
}

Im not sure doing the lifetimes correct for my type?! Can you please check? Can I provide an official example in this repo?

[alice-i-cecile]

That looks correct, but you should probably use the SystemParam derive macro for this :)

If we don't have an example for custom system param we should.

[Bastczuak]

Where should I use SystemParam? Instead of my own type? I'm lost again.

[alice-i-cecile]

#[derive(SystemParam)]
struct RenderingData<'w, 's> {
  camera: Res<'w, Camera>,
  transform_data: Query<'w, 's, &'static Transform>,
);

Like so :)

Although that's not strictly needed; you can just use

  let mut render_state = SystemState::<(Res<Camera>, Query<&Transform>)>::new(&mut world);