WebGL2 support (#3039)

# Objective

Make possible to use wgpu gles backend on in the browser (wasm32 + WebGL2). 

## Solution

It is built on top of old @cart patch initializing windows before wgpu. Also:
- initializes wgpu with `Backends::GL` and proper `wgpu::Limits` on wasm32
- changes default texture format to `wgpu::TextureFormat::Rgba8UnormSrgb`



Co-authored-by: Mariusz Kryński <mrk@sed.pl>

crates/bevy_internal/src/default_plugins.rs

@@ -119,6 +119,9 @@ impl PluginGroup for PipelinedDefaultPlugins {
         group.add(bevy_asset::AssetPlugin::default());
         group.add(bevy_scene::ScenePlugin::default());
 
+        #[cfg(feature = "bevy_winit")]
+        group.add(bevy_winit::WinitPlugin::default());
+
         #[cfg(feature = "bevy_render2")]
         {
             group.add(bevy_render2::RenderPlugin::default());
@@ -137,8 +140,5 @@ impl PluginGroup for PipelinedDefaultPlugins {
             #[cfg(feature = "bevy_gltf2")]
             group.add(bevy_gltf2::GltfPlugin::default());
         }
-
-        #[cfg(feature = "bevy_winit")]
-        group.add(bevy_winit::WinitPlugin::default());
     }
 }

crates/bevy_winit/src/lib.rs

@@ -43,6 +43,9 @@ impl Plugin for WinitPlugin {
         app.init_resource::<WinitWindows>()
             .set_runner(winit_runner)
             .add_system_to_stage(CoreStage::PostUpdate, change_window.exclusive_system());
+        let mut event_loop = EventLoop::new();
+        handle_initial_window_events(&mut app.world, &mut event_loop);
+        app.insert_non_send_resource(event_loop);
     }
 }
 
@@ -207,21 +210,22 @@ where
 }
 
 pub fn winit_runner(app: App) {
-    winit_runner_with(app, EventLoop::new());
+    winit_runner_with(app);
 }
 
-#[cfg(any(
-    target_os = "linux",
-    target_os = "dragonfly",
-    target_os = "freebsd",
-    target_os = "netbsd",
-    target_os = "openbsd"
-))]
-pub fn winit_runner_any_thread(app: App) {
-    winit_runner_with(app, EventLoop::new_any_thread());
-}
-
-pub fn winit_runner_with(mut app: App, mut event_loop: EventLoop<()>) {
+// #[cfg(any(
+//     target_os = "linux",
+//     target_os = "dragonfly",
+//     target_os = "freebsd",
+//     target_os = "netbsd",
+//     target_os = "openbsd"
+// ))]
+// pub fn winit_runner_any_thread(app: App) {
+//     winit_runner_with(app, EventLoop::new_any_thread());
+// }
+
+pub fn winit_runner_with(mut app: App) {
+    let mut event_loop = app.world.remove_non_send::<EventLoop<()>>().unwrap();
     let mut create_window_event_reader = ManualEventReader::<CreateWindow>::default();
     let mut app_exit_event_reader = ManualEventReader::<AppExit>::default();
     app.world.insert_non_send(event_loop.create_proxy());
@@ -525,3 +529,22 @@ fn handle_create_window_events(
         });
     }
 }
+
+fn handle_initial_window_events(world: &mut World, event_loop: &EventLoop<()>) {
+    let world = world.cell();
+    let mut winit_windows = world.get_resource_mut::<WinitWindows>().unwrap();
+    let mut windows = world.get_resource_mut::<Windows>().unwrap();
+    let mut create_window_events = world.get_resource_mut::<Events<CreateWindow>>().unwrap();
+    let mut window_created_events = world.get_resource_mut::<Events<WindowCreated>>().unwrap();
+    for create_window_event in create_window_events.drain() {
+        let window = winit_windows.create_window(
+            event_loop,
+            create_window_event.id,
+            &create_window_event.descriptor,
+        );
+        windows.add(window);
+        window_created_events.send(WindowCreated {
+            id: create_window_event.id,
+        });
+    }
+}

pipelined/bevy_render2/Cargo.toml

@@ -45,6 +45,9 @@ parking_lot = "0.11.0"
 regex = "1.5"
 crevice = { path = "../../crates/crevice", version = "0.6.0" }
 
+[target.'cfg(target_arch = "wasm32")'.dependencies]
+wgpu = { version = "0.11.0", features = ["spirv", "webgl"] }
+
 [features]
 png = ["image/png"]
 hdr = ["image/hdr"]

pipelined/bevy_render2/src/lib.rs

@@ -85,15 +85,40 @@ struct ScratchRenderWorld(World);
 
 impl Plugin for RenderPlugin {
     fn build(&self, app: &mut App) {
-        let (instance, device, queue) =
-            futures_lite::future::block_on(renderer::initialize_renderer(
-                wgpu::util::backend_bits_from_env().unwrap_or(Backends::PRIMARY),
-                &wgpu::RequestAdapterOptions {
-                    power_preference: wgpu::PowerPreference::HighPerformance,
-                    ..Default::default()
+        let default_backend = if cfg!(not(target_arch = "wasm32")) {
+            Backends::PRIMARY
+        } else {
+            Backends::GL
+        };
+        let backends = wgpu::util::backend_bits_from_env().unwrap_or(default_backend);
+        let instance = wgpu::Instance::new(backends);
+        let surface = {
+            let world = app.world.cell();
+            let windows = world.get_resource_mut::<bevy_window::Windows>().unwrap();
+            let raw_handle = windows.get_primary().map(|window| unsafe {
+                let handle = window.raw_window_handle().get_handle();
+                instance.create_surface(&handle)
+            });
+            raw_handle
+        };
+        let (device, queue) = futures_lite::future::block_on(renderer::initialize_renderer(
+            &instance,
+            &wgpu::RequestAdapterOptions {
+                power_preference: wgpu::PowerPreference::HighPerformance,
+                compatible_surface: surface.as_ref(),
+                ..Default::default()
+            },
+            &wgpu::DeviceDescriptor {
+                features: wgpu::Features::TEXTURE_ADAPTER_SPECIFIC_FORMAT_FEATURES,
+                #[cfg(not(target_arch = "wasm32"))]
+                limits: wgpu::Limits::default(),
+                #[cfg(target_arch = "wasm32")]
+                limits: wgpu::Limits {
+                    ..wgpu::Limits::downlevel_webgl2_defaults()
                 },
-                &wgpu::DeviceDescriptor::default(),
-            ));
+                ..Default::default()
+            },
+        ));
         app.insert_resource(device.clone())
             .insert_resource(queue.clone())
             .add_asset::<Shader>()

pipelined/bevy_render2/src/renderer/mod.rs

@@ -42,12 +42,10 @@ pub type RenderQueue = Arc<Queue>;
 pub type RenderInstance = Instance;
 
 pub async fn initialize_renderer(
-    backends: Backends,
+    instance: &Instance,
     request_adapter_options: &RequestAdapterOptions<'_>,
     device_descriptor: &DeviceDescriptor<'_>,
-) -> (RenderInstance, RenderDevice, RenderQueue) {
-    let instance = wgpu::Instance::new(backends);
-
+) -> (RenderDevice, RenderQueue) {
     let adapter = instance
         .request_adapter(request_adapter_options)
         .await
@@ -72,7 +70,7 @@ pub async fn initialize_renderer(
         .unwrap();
     let device = Arc::new(device);
     let queue = Arc::new(queue);
-    (instance, RenderDevice::from(device), queue)
+    (RenderDevice::from(device), queue)
 }
 
 pub struct RenderContext {

pipelined/bevy_render2/src/texture/mod.rs

@@ -42,7 +42,7 @@ pub trait BevyDefault {
 
 impl BevyDefault for wgpu::TextureFormat {
     fn bevy_default() -> Self {
-        if cfg!(target_os = "android") {
+        if cfg!(target_os = "android") || cfg!(target_arch = "wasm32") {
             // Bgra8UnormSrgb texture missing on some Android devices
             wgpu::TextureFormat::Rgba8UnormSrgb
         } else {