Add RenderScheduleOrder resource to allow for RenderApp Schedule changes

crates/bevy_render/src/lib.rs

@@ -99,7 +99,10 @@ use batching::gpu_preprocessing::BatchingPlugin;
 use bevy_app::{App, AppLabel, Plugin, SubApp};
 use bevy_asset::{AssetApp, AssetServer};
 use bevy_derive::Deref;
-use bevy_ecs::{prelude::*, schedule::ScheduleLabel};
+use bevy_ecs::{
+    prelude::*,
+    schedule::{InternedScheduleLabel, ScheduleLabel},
+};
 use bevy_platform::time::Instant;
 use bevy_shader::{load_shader_library, Shader, ShaderLoader};
 use bevy_time::TimeSender;
@@ -233,11 +236,48 @@ impl GpuResourceAppExt for SubApp {
     }
 }
 
-/// The render recovery schedule. This schedule runs the [`Render`] schedule if
+/// The render recovery schedule. This schedule runs the [`RenderScheduleOrder`] schedules if
 /// we are in [`RenderState::Ready`], and is otherwise hidden from users.
 #[derive(ScheduleLabel, Debug, Hash, PartialEq, Eq, Clone)]
 struct RenderRecovery;
 
+/// Defines the schedules to be run for the rendering, including their order.
+#[derive(Resource, Debug)]
+pub struct RenderScheduleOrder {
+    /// The labels to run for the rendering schedule (in the order they will be run).
+    pub labels: Vec<InternedScheduleLabel>,
+}
+
+impl Default for RenderScheduleOrder {
+    fn default() -> Self {
+        Self {
+            labels: vec![Render.intern()],
+        }
+    }
+}
+
+impl RenderScheduleOrder {
+    /// Adds the given `schedule` after the `after` schedule
+    pub fn insert_after(&mut self, after: impl ScheduleLabel, schedule: impl ScheduleLabel) {
+        let index = self
+            .labels
+            .iter()
+            .position(|current| (**current).eq(&after))
+            .unwrap_or_else(|| panic!("Expected {after:?} to exist"));
+        self.labels.insert(index + 1, schedule.intern());
+    }
+
+    /// Adds the given `schedule` before the `before` schedule
+    pub fn insert_before(&mut self, before: impl ScheduleLabel, schedule: impl ScheduleLabel) {
+        let index = self
+            .labels
+            .iter()
+            .position(|current| (**current).eq(&before))
+            .unwrap_or_else(|| panic!("Expected {before:?} to exist"));
+        self.labels.insert(index, schedule.intern());
+    }
+}
+
 /// The main render schedule.
 #[derive(ScheduleLabel, Debug, Hash, PartialEq, Eq, Clone, Default)]
 pub struct Render;
@@ -341,6 +381,7 @@ impl Plugin for RenderPlugin {
         app.init_resource::<RenderAssetBytesPerFrame>()
             .init_resource::<RenderErrorHandler>();
         if let Some(render_app) = app.get_sub_app_mut(RenderApp) {
+            render_app.init_resource::<RenderScheduleOrder>();
             render_app.init_resource::<RenderAssetBytesPerFrameLimiter>();
             render_app.init_gpu_resource::<renderer::PendingCommandBuffers>();
             render_app.insert_resource(sender);
@@ -415,7 +456,11 @@ fn renderer_is_ready(state: Res<RenderState>) -> bool {
 }
 
 fn run_render_schedule(world: &mut World) {
-    world.run_schedule(Render);
+    world.resource_scope(|world, order: Mut<RenderScheduleOrder>| {
+        for &label in &order.labels {
+            let _ = world.try_run_schedule(label);
+        }
+    });
 }
 
 fn send_time(time_sender: Res<TimeSender>) {