bevy_render/
extract_resource.rs

1use core::marker::PhantomData;
2
3use bevy_app::{App, Plugin};
4use bevy_ecs::{component::Mutable, prelude::*};
5pub use bevy_render_macros::ExtractResource;
6use bevy_utils::once;
7
8use crate::{Extract, ExtractSchedule, RenderApp};
9
10/// Describes how a resource gets extracted for rendering.
11///
12/// Therefore the resource is transferred from the "main world" into the "render world"
13/// in the [`ExtractSchedule`] step.
14///
15/// The marker type `F` is only used as a way to bypass the orphan rules. To
16/// implement the trait for a foreign type you can use a local type as the
17/// marker, e.g. the type of the plugin that calls [`ExtractResourcePlugin`].
18pub trait ExtractResource<F = ()>: Resource {
19    type Source: Resource;
20
21    /// Defines how the resource is transferred into the "render world".
22    fn extract_resource(source: &Self::Source) -> Self;
23}
24
25/// This plugin extracts the resources into the "render world".
26///
27/// Therefore it sets up the[`ExtractSchedule`] step
28/// for the specified [`Resource`].
29///
30/// The marker type `F` is only used as a way to bypass the orphan rules. To
31/// implement the trait for a foreign type you can use a local type as the
32/// marker, e.g. the type of the plugin that calls [`ExtractResourcePlugin`].
33pub struct ExtractResourcePlugin<R: ExtractResource<F>, F = ()>(PhantomData<(R, F)>);
34
35impl<R: ExtractResource<F>, F> Default for ExtractResourcePlugin<R, F> {
36    fn default() -> Self {
37        Self(PhantomData)
38    }
39}
40
41impl<R: ExtractResource<F, Mutability = Mutable>, F: 'static + Send + Sync> Plugin
42    for ExtractResourcePlugin<R, F>
43{
44    fn build(&self, app: &mut App) {
45        if let Some(render_app) = app.get_sub_app_mut(RenderApp) {
46            render_app.add_systems(ExtractSchedule, extract_resource::<R, F>);
47        } else {
48            once!(bevy_log::error!(
49                "Render app did not exist when trying to add `extract_resource` for <{}>.",
50                core::any::type_name::<R>()
51            ));
52        }
53    }
54}
55
56/// This system extracts the resource of the corresponding [`Resource`] type
57pub fn extract_resource<R: ExtractResource<F, Mutability = Mutable>, F>(
58    mut commands: Commands,
59    main_resource: Extract<Option<Res<R::Source>>>,
60    target_resource: Option<ResMut<R>>,
61) {
62    if let Some(main_resource) = main_resource.as_ref() {
63        if let Some(mut target_resource) = target_resource {
64            if main_resource.is_changed() {
65                *target_resource = R::extract_resource(main_resource);
66            }
67        } else {
68            #[cfg(debug_assertions)]
69            if !main_resource.is_added() {
70                once!(bevy_log::warn!(
71                    "Removing resource {} from render world not expected, adding using `Commands`.
72                This may decrease performance",
73                    core::any::type_name::<R>()
74                ));
75            }
76
77            commands.insert_resource(R::extract_resource(main_resource));
78        }
79    }
80}
bevy_render/extract_resource.rs

bevy_render/
extract_resource.rs
