4ae6a66481
# Objective
From my understanding, although resources are not meant to be created
and removed at every frame, they are still meant to be created
dynamically during the lifetime of the App.
But because the extract_resource API does not allow optional resources
from the main world, it's impossible to use resources in the render
phase that were not created before the render sub-app itself.
## Solution
Because the ECS engine already allows for system parameters to be
`Option<Res>`, it just had to be added.
---
## Changelog
- Changed
- `extract_resource` now takes an optional main world resource
- Fixed
- `ExtractResourcePlugin` doesn't cause panics anymore if the resource
is not already inserted
66 lines
2.2 KiB
Rust
66 lines
2.2 KiB
Rust
use std::marker::PhantomData;
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use bevy_app::{App, Plugin};
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use bevy_ecs::prelude::*;
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pub use bevy_render_macros::ExtractResource;
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use crate::{Extract, ExtractSchedule, RenderApp};
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/// Describes how a resource gets extracted for rendering.
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///
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/// Therefore the resource is transferred from the "main world" into the "render world"
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/// in the [`ExtractSchedule`] step.
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pub trait ExtractResource: Resource {
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type Source: Resource;
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/// Defines how the resource is transferred into the "render world".
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fn extract_resource(source: &Self::Source) -> Self;
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}
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/// This plugin extracts the resources into the "render world".
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///
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/// Therefore it sets up the[`ExtractSchedule`] step
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/// for the specified [`Resource`].
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pub struct ExtractResourcePlugin<R: ExtractResource>(PhantomData<R>);
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impl<R: ExtractResource> Default for ExtractResourcePlugin<R> {
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fn default() -> Self {
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Self(PhantomData)
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}
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}
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impl<R: ExtractResource> Plugin for ExtractResourcePlugin<R> {
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fn build(&self, app: &mut App) {
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if let Ok(render_app) = app.get_sub_app_mut(RenderApp) {
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render_app.add_systems(ExtractSchedule, extract_resource::<R>);
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}
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}
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}
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/// This system extracts the resource of the corresponding [`Resource`] type
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pub fn extract_resource<R: ExtractResource>(
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mut commands: Commands,
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main_resource: Extract<Option<Res<R::Source>>>,
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target_resource: Option<ResMut<R>>,
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#[cfg(debug_assertions)] mut has_warned_on_remove: Local<bool>,
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) {
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if let Some(main_resource) = main_resource.as_ref() {
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if let Some(mut target_resource) = target_resource {
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if main_resource.is_changed() {
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*target_resource = R::extract_resource(main_resource);
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}
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} else {
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#[cfg(debug_assertions)]
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if !main_resource.is_added() && !*has_warned_on_remove {
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*has_warned_on_remove = true;
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bevy_log::warn!(
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"Removing resource {} from render world not expected, adding using `Commands`.
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This may decrease performance",
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std::any::type_name::<R>()
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);
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}
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commands.insert_resource(R::extract_resource(main_resource));
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}
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}
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}
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