From 1df41b79dd5cec243046b2b5acce496ae3ec1dec Mon Sep 17 00:00:00 2001
From: Kanabenki <lucien.menassol@gmail.com>
Date: Sat, 20 Apr 2024 01:09:30 +0200
Subject: [PATCH] Expose `desired_maximum_frame_latency` through window
 creation (#12954)

# Objective

- Closes #12930.

## Solution

- Add a corresponding optional field on `Window` and `ExtractedWindow`

---

## Changelog

### Added

- `wgpu`'s `desired_maximum_frame_latency` is exposed through window
creation. This can be used to override the default maximum number of
queued frames on the GPU (currently 2).

## Migration Guide

- The `desired_maximum_frame_latency` field must be added to instances
of `Window` and `ExtractedWindow` where all fields are explicitly
specified.
---
 crates/bevy_render/src/view/window/mod.rs | 19 +++++++++++++------
 crates/bevy_window/src/window.rs          | 12 ++++++++++++
 2 files changed, 25 insertions(+), 6 deletions(-)

diff --git a/crates/bevy_render/src/view/window/mod.rs b/crates/bevy_render/src/view/window/mod.rs
index 72a23baea4f8f..762771a41edd5 100644
--- a/crates/bevy_render/src/view/window/mod.rs
+++ b/crates/bevy_render/src/view/window/mod.rs
@@ -15,6 +15,7 @@ use bevy_window::{
     CompositeAlphaMode, PresentMode, PrimaryWindow, RawHandleWrapper, Window, WindowClosed,
 };
 use std::{
+    num::NonZeroU32,
     ops::{Deref, DerefMut},
     sync::PoisonError,
 };
@@ -66,6 +67,7 @@ pub struct ExtractedWindow {
     pub physical_width: u32,
     pub physical_height: u32,
     pub present_mode: PresentMode,
+    pub desired_maximum_frame_latency: Option<NonZeroU32>,
     /// Note: this will not always be the swap chain texture view. When taking a screenshot,
     /// this will point to an alternative texture instead to allow for copying the render result
     /// to CPU memory.
@@ -136,6 +138,7 @@ fn extract_windows(
             physical_width: new_width,
             physical_height: new_height,
             present_mode: window.present_mode,
+            desired_maximum_frame_latency: window.desired_maximum_frame_latency,
             swap_chain_texture: None,
             swap_chain_texture_view: None,
             size_changed: false,
@@ -429,6 +432,12 @@ pub fn need_surface_configuration(
     false
 }
 
+// 2 is wgpu's default/what we've been using so far.
+// 1 is the minimum, but may cause lower framerates due to the cpu waiting for the gpu to finish
+// all work for the previous frame before starting work on the next frame, which then means the gpu
+// has to wait for the cpu to finish to start on the next frame.
+const DEFAULT_DESIRED_MAXIMUM_FRAME_LATENCY: u32 = 2;
+
 /// Creates window surfaces.
 pub fn create_surfaces(
     // By accessing a NonSend resource, we tell the scheduler to put this system on the main thread,
@@ -488,12 +497,10 @@ pub fn create_surfaces(
                         PresentMode::AutoVsync => wgpu::PresentMode::AutoVsync,
                         PresentMode::AutoNoVsync => wgpu::PresentMode::AutoNoVsync,
                     },
-                    // TODO: Expose this as a setting somewhere
-                    // 2 is wgpu's default/what we've been using so far.
-                    // 1 is the minimum, but may cause lower framerates due to the cpu waiting for the gpu to finish
-                    // all work for the previous frame before starting work on the next frame, which then means the gpu
-                    // has to wait for the cpu to finish to start on the next frame.
-                    desired_maximum_frame_latency: 2,
+                    desired_maximum_frame_latency: window
+                        .desired_maximum_frame_latency
+                        .map(NonZeroU32::get)
+                        .unwrap_or(DEFAULT_DESIRED_MAXIMUM_FRAME_LATENCY),
                     alpha_mode: match window.alpha_mode {
                         CompositeAlphaMode::Auto => wgpu::CompositeAlphaMode::Auto,
                         CompositeAlphaMode::Opaque => wgpu::CompositeAlphaMode::Opaque,
diff --git a/crates/bevy_window/src/window.rs b/crates/bevy_window/src/window.rs
index 216dbf8abd446..d80f070a1657b 100644
--- a/crates/bevy_window/src/window.rs
+++ b/crates/bevy_window/src/window.rs
@@ -1,3 +1,5 @@
+use std::num::NonZeroU32;
+
 use bevy_ecs::{
     entity::{Entity, EntityMapper, MapEntities},
     prelude::{Component, ReflectComponent},
@@ -270,6 +272,15 @@ pub struct Window {
     ///
     /// - Only supported on Windows.
     pub skip_taskbar: bool,
+    /// Optional hint given to the rendering API regarding the maximum number of queued frames admissible on the GPU.
+    ///
+    /// Given values are usually within the 1-3 range. If not provided, this will default to 2.
+    ///
+    /// See [`wgpu::SurfaceConfiguration::desired_maximum_frame_latency`].
+    ///
+    /// [`wgpu::SurfaceConfiguration::desired_maximum_frame_latency`]:
+    /// https://docs.rs/wgpu/latest/wgpu/type.SurfaceConfiguration.html#structfield.desired_maximum_frame_latency
+    pub desired_maximum_frame_latency: Option<NonZeroU32>,
 }
 
 impl Default for Window {
@@ -299,6 +310,7 @@ impl Default for Window {
             window_theme: None,
             visible: true,
             skip_taskbar: false,
+            desired_maximum_frame_latency: None,
         }
     }
 }