use std::marker::PhantomData;
use bevy_app::{App, Plugin};
use bevy_ecs::prelude::*;
pub use bevy_render_macros::ExtractResource;
use crate::{Extract, ExtractSchedule, RenderApp};
pub trait ExtractResource: Resource {
type Source: Resource;
fn extract_resource(source: &Self::Source) -> Self;
}
pub struct ExtractResourcePlugin<R: ExtractResource>(PhantomData<R>);
impl<R: ExtractResource> Default for ExtractResourcePlugin<R> {
fn default() -> Self {
Self(PhantomData)
}
}
impl<R: ExtractResource> Plugin for ExtractResourcePlugin<R> {
fn build(&self, app: &mut App) {
if let Some(render_app) = app.get_sub_app_mut(RenderApp) {
render_app.add_systems(ExtractSchedule, extract_resource::<R>);
} else {
bevy_utils::error_once!(
"Render app did not exist when trying to add `extract_resource` for <{}>.",
std::any::type_name::<R>()
);
}
}
}
pub fn extract_resource<R: ExtractResource>(
mut commands: Commands,
main_resource: Extract<Option<Res<R::Source>>>,
target_resource: Option<ResMut<R>>,
) {
if let Some(main_resource) = main_resource.as_ref() {
if let Some(mut target_resource) = target_resource {
if main_resource.is_changed() {
*target_resource = R::extract_resource(main_resource);
}
} else {
#[cfg(debug_assertions)]
if !main_resource.is_added() {
bevy_utils::warn_once!(
"Removing resource {} from render world not expected, adding using `Commands`.
This may decrease performance",
std::any::type_name::<R>()
);
}
commands.insert_resource(R::extract_resource(main_resource));
}
}
}