bevy_render/
extract_resource.rs

1use core::marker::PhantomData;
2
3use bevy_app::{App, Plugin};
4use bevy_ecs::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.
14pub trait ExtractResource: Resource {
15    type Source: Resource;
16
17    /// Defines how the resource is transferred into the "render world".
18    fn extract_resource(source: &Self::Source) -> Self;
19}
20
21/// This plugin extracts the resources into the "render world".
22///
23/// Therefore it sets up the[`ExtractSchedule`] step
24/// for the specified [`Resource`].
25pub struct ExtractResourcePlugin<R: ExtractResource>(PhantomData<R>);
26
27impl<R: ExtractResource> Default for ExtractResourcePlugin<R> {
28    fn default() -> Self {
29        Self(PhantomData)
30    }
31}
32
33impl<R: ExtractResource> Plugin for ExtractResourcePlugin<R> {
34    fn build(&self, app: &mut App) {
35        if let Some(render_app) = app.get_sub_app_mut(RenderApp) {
36            render_app.add_systems(ExtractSchedule, extract_resource::<R>);
37        } else {
38            once!(tracing::error!(
39                "Render app did not exist when trying to add `extract_resource` for <{}>.",
40                core::any::type_name::<R>()
41            ));
42        }
43    }
44}
45
46/// This system extracts the resource of the corresponding [`Resource`] type
47pub fn extract_resource<R: ExtractResource>(
48    mut commands: Commands,
49    main_resource: Extract<Option<Res<R::Source>>>,
50    target_resource: Option<ResMut<R>>,
51) {
52    if let Some(main_resource) = main_resource.as_ref() {
53        if let Some(mut target_resource) = target_resource {
54            if main_resource.is_changed() {
55                *target_resource = R::extract_resource(main_resource);
56            }
57        } else {
58            #[cfg(debug_assertions)]
59            if !main_resource.is_added() {
60                once!(tracing::warn!(
61                    "Removing resource {} from render world not expected, adding using `Commands`.
62                This may decrease performance",
63                    core::any::type_name::<R>()
64                ));
65            }
66
67            commands.insert_resource(R::extract_resource(main_resource));
68        }
69    }
70}
bevy_render/extract_resource.rs

bevy_render/
extract_resource.rs
