[rs] Merge #693

693: Expose get_swap_chain_preferred_format r=kvark a=manugildev

Fixes #691

This functionality was committed in gfx-rs/wgpu@6f1d614 but never exposed to `wgpu-rs`.

Problem: Examples made use of `wgpu::TextureFormat::Bgra8UnormSrgb` but that's unreliable and according to the [API](https://gpuweb.github.io/gpuweb/#dom-gpucanvascontext-getswapchainpreferredformat) this method is the way of properly obtaining an optimal texture format for the `SwapChain` based on the platform.

- [x]  Expose `get_swap_chain_preferred_format()` on Device
- [x]  Use `TextureFormat::Bgra8Unorm` for [web.rs](e00ef5d584/src/backend/web.rs (L970))
- [x]  Update [framework.rs](e00ef5d584/examples/framework.rs (L227)) and examples to call this new method

Co-authored-by: Manuel Gil <manugildev@gmail.com>

wgpu/examples/framework.rs

@@ -224,12 +224,7 @@ fn start<E: Example>(
 
     let mut sc_desc = wgpu::SwapChainDescriptor {
         usage: wgpu::TextureUsage::RENDER_ATTACHMENT,
-        // TODO: Allow srgb unconditionally
-        format: if cfg!(target_arch = "wasm32") {
-            wgpu::TextureFormat::Bgra8Unorm
-        } else {
-            wgpu::TextureFormat::Bgra8UnormSrgb
-        },
+        format: device.get_swap_chain_preferred_format(),
         width: size.width,
         height: size.height,
         present_mode: wgpu::PresentMode::Mailbox,

wgpu/examples/hello-triangle/main.rs

@@ -5,7 +5,7 @@ use winit::{
     window::Window,
 };
 
-async fn run(event_loop: EventLoop<()>, window: Window, swapchain_format: wgpu::TextureFormat) {
+async fn run(event_loop: EventLoop<()>, window: Window) {
     let size = window.inner_size();
     let instance = wgpu::Instance::new(wgpu::BackendBit::PRIMARY);
     let surface = unsafe { instance.create_surface(&window) };
@@ -44,6 +44,8 @@ async fn run(event_loop: EventLoop<()>, window: Window, swapchain_format: wgpu::
         push_constant_ranges: &[],
     });
 
+    let swapchain_format = device.get_swap_chain_preferred_format();
+
     let render_pipeline = device.create_render_pipeline(&wgpu::RenderPipelineDescriptor {
         label: None,
         layout: Some(&pipeline_layout),
@@ -138,7 +140,7 @@ fn main() {
     {
         subscriber::initialize_default_subscriber(None);
         // Temporarily avoid srgb formats for the swapchain on the web
-        futures::executor::block_on(run(event_loop, window, wgpu::TextureFormat::Bgra8UnormSrgb));
+        futures::executor::block_on(run(event_loop, window));
     }
     #[cfg(target_arch = "wasm32")]
     {
@@ -154,6 +156,6 @@ fn main() {
                     .ok()
             })
             .expect("couldn't append canvas to document body");
-        wasm_bindgen_futures::spawn_local(run(event_loop, window, wgpu::TextureFormat::Bgra8Unorm));
+        wasm_bindgen_futures::spawn_local(run(event_loop, window));
     }
 }

wgpu/examples/hello-windows/main.rs

@@ -27,12 +27,12 @@ impl ViewportDesc {
         }
     }
 
-    fn build(self, device: &wgpu::Device, swapchain_format: wgpu::TextureFormat) -> Viewport {
+    fn build(self, device: &wgpu::Device) -> Viewport {
         let size = self.window.inner_size();
 
         let sc_desc = wgpu::SwapChainDescriptor {
             usage: wgpu::TextureUsage::RENDER_ATTACHMENT,
-            format: swapchain_format,
+            format: device.get_swap_chain_preferred_format(),
             width: size.width,
             height: size.height,
             present_mode: wgpu::PresentMode::Fifo,
@@ -62,11 +62,7 @@ impl Viewport {
     }
 }
 
-async fn run(
-    event_loop: EventLoop<()>,
-    viewports: Vec<(Window, wgpu::Color)>,
-    swapchain_format: wgpu::TextureFormat,
-) {
+async fn run(event_loop: EventLoop<()>, viewports: Vec<(Window, wgpu::Color)>) {
     let instance = wgpu::Instance::new(wgpu::BackendBit::PRIMARY);
     let viewports: Vec<_> = viewports
         .into_iter()
@@ -96,7 +92,7 @@ async fn run(
 
     let mut viewports: HashMap<WindowId, Viewport> = viewports
         .into_iter()
-        .map(|desc| (desc.window.id(), desc.build(&device, swapchain_format)))
+        .map(|desc| (desc.window.id(), desc.build(&device)))
         .collect();
 
     event_loop.run(move |event, _, control_flow| {
@@ -195,11 +191,7 @@ fn main() {
 
         subscriber::initialize_default_subscriber(None);
         // Temporarily avoid srgb formats for the swapchain on the web
-        futures::executor::block_on(run(
-            event_loop,
-            viewports,
-            wgpu::TextureFormat::Bgra8UnormSrgb,
-        ));
+        futures::executor::block_on(run(event_loop, viewports));
     }
     #[cfg(target_arch = "wasm32")]
     {

wgpu/src/backend/direct.rs

@@ -4,7 +4,7 @@ use crate::{
     CommandEncoderDescriptor, ComputePassDescriptor, ComputePipelineDescriptor, Features, Label,
     Limits, LoadOp, MapMode, Operations, PipelineLayoutDescriptor, RenderBundleEncoderDescriptor,
     RenderPipelineDescriptor, SamplerDescriptor, ShaderModuleDescriptor, ShaderSource,
-    SwapChainStatus, TextureDescriptor, TextureViewDescriptor,
+    SwapChainStatus, TextureDescriptor, TextureFormat, TextureViewDescriptor,
 };
 
 use arrayvec::ArrayVec;
@@ -707,6 +707,15 @@ impl crate::Context for Context {
         }
     }
 
+    fn device_get_swap_chain_preferred_format(&self, device: &Self::DeviceId) -> TextureFormat {
+        let global = &self.0;
+        match wgc::gfx_select!(device.id => global.device_get_swap_chain_preferred_format(device.id))
+        {
+            Ok(swap_chain_preferred_format) => swap_chain_preferred_format,
+            Err(err) => self.handle_error_fatal(err, "Device::get_swap_chain_preferred_format"),
+        }
+    }
+
     fn device_create_swap_chain(
         &self,
         device: &Self::DeviceId,

wgpu/src/backend/web.rs

@@ -962,6 +962,14 @@ impl crate::Context for Context {
         wgt::Limits::default()
     }
 
+    fn device_get_swap_chain_preferred_format(
+        &self,
+        device: &Self::DeviceId,
+    ) -> wgt::TextureFormat {
+        // TODO: web-sys bindings need to be updated to not return a promise
+        wgt::TextureFormat::Bgra8Unorm
+    }
+
     fn device_create_swap_chain(
         &self,
         device: &Self::DeviceId,

wgpu/src/lib.rs

@@ -196,6 +196,7 @@ trait Context: Debug + Send + Sized + Sync {
 
     fn device_features(&self, device: &Self::DeviceId) -> Features;
     fn device_limits(&self, device: &Self::DeviceId) -> Limits;
+    fn device_get_swap_chain_preferred_format(&self, device: &Self::DeviceId) -> TextureFormat;
     fn device_create_swap_chain(
         &self,
         device: &Self::DeviceId,
@@ -1428,6 +1429,11 @@ impl Device {
         Context::device_limits(&*self.context, &self.id)
     }
 
+    /// Returns an optimal texture format to use for the [`SwapChain`] with this device.
+    pub fn get_swap_chain_preferred_format(&self) -> TextureFormat {
+        Context::device_get_swap_chain_preferred_format(&*self.context, &self.id)
+    }
+
     /// Creates a shader module from either SPIR-V or WGSL source code.
     pub fn create_shader_module(&self, desc: &ShaderModuleDescriptor) -> ShaderModule {
         ShaderModule {