Inheritable Render Layers

[grace125]

Objective

Implements #12461.

Solution

Makes RenderLayers no longer a component, adds components VisibleLayers and InheritedVisibleLayers that work as you'd expect, and VisibleLayers is now required by Visibility.

Testing

These changes work on all of the examples that used to use RenderLayers as a component: pixel_grid_snap, first_person_view_model, order_independent_transparency, and render_to_texture. I have yet to do any benchmarking. It also seems to work in the more hierarchical example I put in showcase.

---

Showcase

Users can now add VisibleLayers to a root component of a mesh, and it will inherit down the tree!

Click to view showcase

use std::f32::consts::PI;

use bevy::prelude::*;
use bevy_render::view::VisibleLayers;

fn main() {
    App::new()
        .add_plugins(DefaultPlugins)
        .add_systems(Startup, setup)
        .add_systems(Update, input)
        .run();
}

#[derive(Component)]
struct Box;

fn setup(mut commands: Commands, asset_server: Res<AssetServer>) {
    commands.spawn((Transform::default(), Visibility::default(), VisibleLayers::layer(1), Name::new("Root"))).with_children(|parent| {

        parent.spawn((
            Name::new("Camera3d"),
            Camera3d::default(),
            Transform::from_xyz(4.0, 4.0, 12.0).looking_at(Vec3::new(0.0, 0.0, 0.5), Vec3::Y),
        ));
    
        parent.spawn((
            Name::new("DirectionalLight"),
            Transform::from_rotation(Quat::from_euler(EulerRot::ZYX, 0.0, 1.0, -PI / 4.)),
            DirectionalLight::default(),
        ));

        parent.spawn((
            Name::new("Box"),
            Transform::default(), 
            Visibility::default(),
            Box
        )).with_child((
            Name::new("BoxScene"),
            SceneRoot(asset_server.load(
                GltfAssetLabel::Scene(0).from_asset("models/GltfPrimitives/gltf_primitives.glb"),
                
            ))
        ));
    });
}

fn input(mut query: Single<&mut VisibleLayers, With<Box>>, input: Res<ButtonInput<KeyCode>>) {
    if input.just_pressed(KeyCode::KeyA) {
        **query = VisibleLayers::Inherited;
    }
    if input.just_pressed(KeyCode::KeyS) {
        **query = VisibleLayers::layer(0);
    }
    if input.just_pressed(KeyCode::KeyD) {
        **query = VisibleLayers::layer(1);
    }
}

Migration Guide

• Replace uses of RenderLayers as a component with VisibleLayers.

[tomara-x]

if i really really want this, what can i do to help?
i fixed the conflicts and i'm testing it. it has everything i need!
can i help in some way?

edit: never mind, i was given the generic component propagation pr :D (#17575)

[grace125]

I forgot I left this PR open! I realised everything I was doing could be done in userspace, so I did that. A generic solution would be better, it doesn't really make sense to have ad-hoc propagation for everything that might need it.