Expose maximum_frame_latency

CHANGELOG.md

@@ -66,6 +66,7 @@ Wgpu now exposes backend feature for the Direct3D 12 (`dx12`) and Metal (`metal`
 - No longer validate surfaces against their allowed extent range on configure. This caused warnings that were almost impossible to avoid. As before, the resulting behavior depends on the compositor. By @wumpf in [#4796](https://github.com/gfx-rs/wgpu/pull/4796)
 - Added support for the float32-filterable feature. By @almarklein in [#4759](https://github.com/gfx-rs/wgpu/pull/4759)
 - wgpu and wgpu-core features are now documented on docs.rs. By @wumpf in [#4886](https://github.com/gfx-rs/wgpu/pull/4886)
+- `SurfaceConfiguration` now exposes `desired_swap_chain_size` which was previously hard-coded to 3. By setting it to 2 you can reduce latency. By picking a large value you can ensure higher throughput. By @emilk & @wumpf in [#4899](https://github.com/gfx-rs/wgpu/pull/4899)
 
 #### OpenGL
 - `@builtin(instance_index)` now properly reflects the range provided in the draw call instead of always counting from 0. By @cwfitzgerald in [#4722](https://github.com/gfx-rs/wgpu/pull/4722).

examples/src/framework.rs

@@ -571,6 +571,7 @@ impl<E: Example + wgpu::WasmNotSendSync> From<ExampleTestParams<E>>
                         format,
                         width: params.width,
                         height: params.height,
+                        desired_swap_chain_size: 3,
                         present_mode: wgpu::PresentMode::Fifo,
                         alpha_mode: wgpu::CompositeAlphaMode::Auto,
                         view_formats: vec![format],

examples/src/hello_triangle/mod.rs

@@ -72,16 +72,9 @@ async fn run(event_loop: EventLoop<()>, window: Window) {
         multiview: None,
     });
 
-    let mut config = wgpu::SurfaceConfiguration {
-        usage: wgpu::TextureUsages::RENDER_ATTACHMENT,
-        format: swapchain_format,
-        width: size.width,
-        height: size.height,
-        present_mode: wgpu::PresentMode::Fifo,
-        alpha_mode: swapchain_capabilities.alpha_modes[0],
-        view_formats: vec![],
-    };
-
+    let mut config = surface
+        .get_default_config(&adapter, size.width, size.height)
+        .unwrap();
     surface.configure(&device, &config);
 
     let window = &window;

examples/src/hello_windows/mod.rs

@@ -30,20 +30,11 @@ impl ViewportDesc {
 
     fn build(self, adapter: &wgpu::Adapter, device: &wgpu::Device) -> Viewport {
         let size = self.window.inner_size();
-
-        let caps = self.surface.get_capabilities(adapter);
-        let config = wgpu::SurfaceConfiguration {
-            usage: wgpu::TextureUsages::RENDER_ATTACHMENT,
-            format: caps.formats[0],
-            width: size.width,
-            height: size.height,
-            present_mode: wgpu::PresentMode::Fifo,
-            alpha_mode: caps.alpha_modes[0],
-            view_formats: vec![],
-        };
-
+        let config = self
+            .surface
+            .get_default_config(adapter, size.width, size.height)
+            .unwrap();
         self.surface.configure(device, &config);
-
         Viewport { desc: self, config }
     }
 }

examples/src/uniform_values/mod.rs

@@ -192,15 +192,9 @@ impl WgpuContext {
             multiview: None,
         });
 
-        let surface_config = wgpu::SurfaceConfiguration {
-            usage: wgpu::TextureUsages::RENDER_ATTACHMENT,
-            format: swapchain_format,
-            width: size.width,
-            height: size.height,
-            present_mode: wgpu::PresentMode::Fifo,
-            alpha_mode: swapchain_capabilities.alpha_modes[0],
-            view_formats: vec![],
-        };
+        let surface_config = surface
+            .get_default_config(&adapter, size.width, size.height)
+            .unwrap();
         surface.configure(&device, &surface_config);
 
         // (5)

wgpu-core/src/device/global.rs

@@ -1991,7 +1991,8 @@ impl<G: GlobalIdentityHandlerFactory> Global<G> {
                     }
                 }
 
-                let num_frames = present::DESIRED_NUM_FRAMES
+                let num_frames = config
+                    .desired_swap_chain_size
                     .clamp(*caps.swap_chain_sizes.start(), *caps.swap_chain_sizes.end());
                 let mut hal_config = hal::SurfaceConfiguration {
                     swap_chain_size: num_frames,

wgpu-core/src/present.rs

@@ -36,7 +36,6 @@ use thiserror::Error;
 use wgt::SurfaceStatus as Status;
 
 const FRAME_TIMEOUT_MS: u32 = 1000;
-pub const DESIRED_NUM_FRAMES: u32 = 3;
 
 #[derive(Debug)]
 pub(crate) struct Presentation {

wgpu-types/src/lib.rs

@@ -5107,6 +5107,13 @@ pub struct SurfaceConfiguration<V> {
     /// AutoNoVsync will gracefully do a designed sets of fallbacks if their primary modes are
     /// unsupported.
     pub present_mode: PresentMode,
+    /// Desired number of buffers in the swap chain.
+    ///
+    /// Defaults to 3 when created via `wgpu::Surface::get_default_config`.
+    ///
+    /// Recommended to use 3 (or higher) for high throughput, 2 for low latency.
+    /// This is a hint to the backend implementation and will be clamped to the supported range.
+    pub desired_swap_chain_size: u32,
     /// Specifies how the alpha channel of the textures should be handled during compositing.
     pub alpha_mode: CompositeAlphaMode,
     /// Specifies what view formats will be allowed when calling create_view() on texture returned by get_current_texture().
@@ -5126,6 +5133,7 @@ impl<V: Clone> SurfaceConfiguration<V> {
             width: self.width,
             height: self.height,
             present_mode: self.present_mode,
+            desired_swap_chain_size: self.desired_swap_chain_size,
             alpha_mode: self.alpha_mode,
             view_formats: fun(self.view_formats.clone()),
         }

wgpu/src/lib.rs

@@ -5057,6 +5057,7 @@ impl Surface<'_> {
             format: *caps.formats.get(0)?,
             width,
             height,
+            desired_swap_chain_size: 3,
             present_mode: *caps.present_modes.get(0)?,
             alpha_mode: wgt::CompositeAlphaMode::Auto,
             view_formats: vec![],