[Merged by Bors] - Update time by sending frame instant through a channel

crates/bevy_render/Cargo.toml

@@ -38,6 +38,7 @@ bevy_math = { path = "../bevy_math", version = "0.8.0-dev" }
 bevy_mikktspace = { path = "../bevy_mikktspace", version = "0.8.0-dev" }
 bevy_reflect = { path = "../bevy_reflect", version = "0.8.0-dev", features = ["bevy"] }
 bevy_render_macros = { path = "macros", version = "0.8.0-dev" }
+bevy_time = { path = "../bevy_time", version = "0.8.0-dev" }
 bevy_transform = { path = "../bevy_transform", version = "0.8.0-dev" }
 bevy_window = { path = "../bevy_window", version = "0.8.0-dev" }
 bevy_utils = { path = "../bevy_utils", version = "0.8.0-dev" }

crates/bevy_render/src/lib.rs

@@ -183,6 +183,10 @@ impl Plugin for RenderPlugin {
                 .insert_resource(asset_server)
                 .init_resource::<RenderGraph>();
 
+            let (sender, receiver) = bevy_time::create_time_channels();
+            app.insert_resource(receiver);
+            render_app.insert_resource(sender);
+
             app.add_sub_app(RenderApp, render_app, move |app_world, render_app| {
                 #[cfg(feature = "trace")]
                 let _render_span = bevy_utils::tracing::info_span!("renderer subapp").entered();

crates/bevy_render/src/renderer/mod.rs

@@ -11,6 +11,8 @@ use crate::{
     view::{ExtractedWindows, ViewTarget},
 };
 use bevy_ecs::prelude::*;
+use bevy_time::TimeSender;
+use bevy_utils::Instant;
 use std::sync::Arc;
 use wgpu::{AdapterInfo, CommandEncoder, Instance, Queue, RequestAdapterOptions};
 
@@ -73,6 +75,12 @@ pub fn render_system(world: &mut World) {
             tracy.frame_mark = true
         );
     }
+
+    // update the time and send it to the app world
+    let time_sender = world.resource::<TimeSender>();
+    time_sender.0.try_send(Instant::now()).expect(
+        "The TimeSender channel should always be empty during render. You might need to add the bevy::core::time_system to your app.",
+    );
 }
 
 /// This queue is used to enqueue tasks for the GPU to execute asynchronously.

crates/bevy_time/Cargo.toml

@@ -15,3 +15,6 @@ bevy_app = { path = "../bevy_app", version = "0.8.0-dev" }
 bevy_ecs = { path = "../bevy_ecs", version = "0.8.0-dev", features = ["bevy_reflect"] }
 bevy_reflect = { path = "../bevy_reflect", version = "0.8.0-dev", features = ["bevy"] }
 bevy_utils = { path = "../bevy_utils", version = "0.8.0-dev" }
+
+# other
+crossbeam-channel = "0.5.0"

crates/bevy_time/src/lib.rs

@@ -9,6 +9,10 @@ pub use stopwatch::*;
 pub use time::*;
 pub use timer::*;
 
+use bevy_ecs::system::{Local, Res, ResMut};
+use bevy_utils::{tracing::warn, Instant};
+use crossbeam_channel::{Receiver, Sender};
+
 pub mod prelude {
     //! The Bevy Time Prelude.
     #[doc(hidden)]
@@ -41,6 +45,36 @@ impl Plugin for TimePlugin {
     }
 }
 
-fn time_system(mut time: ResMut<Time>) {
-    time.update();
+/// Channel resource used to receive time from render world
+pub struct TimeReceiver(pub Receiver<Instant>);
+/// Channel resource used to send time from render world
+pub struct TimeSender(pub Sender<Instant>);
+
+/// Creates channels used for sending time between render world and app world
+pub fn create_time_channels() -> (TimeSender, TimeReceiver) {
+    // bound the channel to 2 since when pipelined the render phase can finish before
+    // the time system runs.
+    let (s, r) = crossbeam_channel::bounded::<Instant>(2);
+    (TimeSender(s), TimeReceiver(r))
+}
+
+/// The system used to update the [`Time`] used by app logic. If there is a render world the time is sent from
+/// there to this system through channels. Otherwise the time is updated in this system.
+fn time_system(
+    mut time: ResMut<Time>,
+    time_recv: Option<Res<TimeReceiver>>,
+    mut has_received_time: Local<bool>,
+) {
+    if let Some(time_recv) = time_recv {
+        // TODO: delay checking channel on start by 2 frames when pipelined rendering
+        // is enabled. This is to make sure we always read the N-2 frame's time.
+        if let Ok(new_time) = time_recv.0.try_recv() {
+            time.update_with_instant(new_time);
+            *has_received_time = true;
+        } else if *has_received_time {
+            warn!("time_system did not receive time from render world! Calculations depending on the time may be incorrect.");
+        }
+    } else {
+        time.update();
+    }
 }