[wgpu-hal] Allow importing external WGL contexts as with EGL

Author: MarijnS95

CHANGELOG.md

@@ -111,6 +111,7 @@ By @teoxoy [#6134](https://github.com/gfx-rs/wgpu/pull/6134).
 #### GLES
 
 - Replace `winapi` code in WGL wrapper to use the `windows` crate. By @MarijnS95 in [#6006](https://github.com/gfx-rs/wgpu/pull/6006)
+- Implement `Adapter::new_external()` for WGL (just like EGL) to import an external OpenGL ES context. By @MarijnS95 in [#6152](https://github.com/gfx-rs/wgpu/pull/6152)
 
 #### DX12
 

Cargo.lock

@@ -207,8 +207,8 @@ env_logger.workspace = true
 glam.workspace = true # for ray-traced-triangle example
 winit.workspace = true # for "halmark" example
 
-[target.'cfg(not(any(target_arch = "wasm32", windows, target_os = "ios")))'.dev-dependencies]
-glutin-winit = { workspace = true, features = ["egl"] } # for "raw-gles" example
-glutin = { workspace = true, features = ["egl"] } # for "raw-gles" example
+[target.'cfg(not(any(target_arch = "wasm32", target_os = "ios")))'.dev-dependencies]
+glutin-winit = { workspace = true, features = ["egl", "wgl"] } # for "raw-gles" example
+glutin = { workspace = true, features = ["egl", "wgl"] } # for "raw-gles" example
 rwh_05 = { version = "0.5", package = "raw-window-handle" } # temporary compatibility for glutin-winit in "raw-gles" example
 winit = { workspace = true, features = ["rwh_05"] } # for "raw-gles" example

wgpu-hal/Cargo.toml

@@ -10,13 +10,13 @@
 
 extern crate wgpu_hal as hal;
 
-#[cfg(not(any(windows, target_arch = "wasm32", target_os = "ios")))]
+#[cfg(not(any(target_arch = "wasm32", target_os = "ios")))]
 fn main() {
     use std::{ffi::CString, num::NonZeroU32};
 
     use glutin::{
         config::GlConfig as _,
-        context::{NotCurrentGlContext as _, PossiblyCurrentGlContext as _},
+        context::{NotCurrentGlContext as _, PossiblyCurrentGlContext as _, Version},
         display::{GetGlDisplay as _, GlDisplay as _},
         surface::GlSurface as _,
     };
@@ -255,7 +255,6 @@ fn main() {
 }
 
 #[cfg(any(
-    windows,
     all(target_arch = "wasm32", not(target_os = "emscripten")),
     target_os = "ios"
 ))]
@@ -264,7 +263,6 @@ fn main() {
 }
 
 #[cfg(not(any(
-    windows,
     all(target_arch = "wasm32", not(target_os = "emscripten")),
     target_os = "ios"
 )))]

wgpu-hal/examples/raw-gles.rs

@@ -1082,7 +1082,8 @@ impl crate::Instance for Instance {
             unsafe { gl.debug_message_callback(super::gl_debug_message_callback) };
         }
 
-        // Avoid accidental drop when the context is not current.
+        // Wrap in ManuallyDrop to make it easier to "current" the
+        // GL context before dropping this GLOW context.
         let gl = ManuallyDrop::new(gl);
         inner.egl.unmake_current();
 

wgpu-hal/src/gles/egl.rs

@@ -1,11 +1,3 @@
-use glow::HasContext;
-use glutin_wgl_sys::wgl_extra::{
-    Wgl, CONTEXT_CORE_PROFILE_BIT_ARB, CONTEXT_DEBUG_BIT_ARB, CONTEXT_FLAGS_ARB,
-    CONTEXT_PROFILE_MASK_ARB,
-};
-use once_cell::sync::Lazy;
-use parking_lot::{Mutex, MutexGuard, RwLock};
-use raw_window_handle::{RawDisplayHandle, RawWindowHandle};
 use std::{
     collections::HashSet,
     ffi::{c_void, CStr, CString},
@@ -19,6 +11,15 @@ use std::{
     thread,
     time::Duration,
 };
+
+use glow::HasContext;
+use glutin_wgl_sys::wgl_extra::{
+    Wgl, CONTEXT_CORE_PROFILE_BIT_ARB, CONTEXT_DEBUG_BIT_ARB, CONTEXT_FLAGS_ARB,
+    CONTEXT_PROFILE_MASK_ARB,
+};
+use once_cell::sync::Lazy;
+use parking_lot::{Mutex, MutexGuard, RwLock};
+use raw_window_handle::{RawDisplayHandle, RawWindowHandle};
 use wgt::InstanceFlags;
 use windows::{
     core::{Error, PCSTR},
@@ -48,7 +49,10 @@ impl AdapterContext {
     }
 
     pub fn raw_context(&self) -> *mut c_void {
-        self.inner.lock().context.context.0
+        match self.inner.lock().context {
+            Some(ref wgl) => wgl.context.0,
+            None => ptr::null_mut(),
+        }
     }
 
     /// Obtain a lock to the WGL context and get handle to the [`glow::Context`] that can be used to
@@ -62,7 +66,9 @@ impl AdapterContext {
             .try_lock_for(Duration::from_secs(CONTEXT_LOCK_TIMEOUT_SECS))
             .expect("Could not lock adapter context. This is most-likely a deadlock.");
 
-        inner.context.make_current(inner.device.dc).unwrap();
+        if let Some(wgl) = &inner.context {
+            wgl.make_current(inner.device.dc).unwrap()
+        };
 
         AdapterContextLock { inner }
     }
@@ -79,10 +85,11 @@ impl AdapterContext {
             .try_lock_for(Duration::from_secs(CONTEXT_LOCK_TIMEOUT_SECS))
             .expect("Could not lock adapter context. This is most-likely a deadlock.");
 
-        inner
-            .context
-            .make_current(device)
-            .map(|()| AdapterContextLock { inner })
+        if let Some(wgl) = &inner.context {
+            wgl.make_current(device)?;
+        }
+
+        Ok(AdapterContextLock { inner })
     }
 }
 
@@ -101,7 +108,10 @@ impl<'a> std::ops::Deref for AdapterContextLock<'a> {
 
 impl<'a> Drop for AdapterContextLock<'a> {
     fn drop(&mut self) {
-        self.inner.context.unmake_current().unwrap();
+        // EGL performs a .take() here but that causes issues with drop ordering
+        if let Some(wgl) = &self.inner.context {
+            wgl.unmake_current().unwrap()
+        }
     }
 }
 
@@ -136,7 +146,7 @@ unsafe impl Sync for WglContext {}
 struct Inner {
     gl: ManuallyDrop<glow::Context>,
     device: InstanceDevice,
-    context: WglContext,
+    context: Option<WglContext>,
 }
 
 impl Drop for Inner {
@@ -150,8 +160,14 @@ impl Drop for Inner {
 
         // Context must be current when dropped. See safety docs on
         // `glow::HasContext`.
-        self.context.make_current(self.device.dc).unwrap();
-        let _guard = CurrentGuard(&self.context);
+        //
+        // NOTE: This is only set to `None` by `Adapter::new_external` which
+        // requires the context to be current when anything that may be holding
+        // the `Arc<AdapterShared>` is dropped.
+        let _guard = self.context.as_ref().map(|wgl| {
+            wgl.make_current(self.device.dc).unwrap();
+            CurrentGuard(wgl)
+        });
         // SAFETY: Field not used after this.
         unsafe { ManuallyDrop::drop(&mut self.gl) };
     }
@@ -515,7 +531,8 @@ impl crate::Instance for Instance {
             unsafe { gl.debug_message_callback(super::gl_debug_message_callback) };
         }
 
-        // Avoid accidental drop when the context is not current.
+        // Wrap in ManuallyDrop to make it easier to "current" the
+        // GL context before dropping this GLOW context.
         let gl = ManuallyDrop::new(gl);
         context.unmake_current().map_err(|e| {
             crate::InstanceError::with_source(
@@ -528,7 +545,7 @@ impl crate::Instance for Instance {
             inner: Arc::new(Mutex::new(Inner {
                 device,
                 gl,
-                context,
+                context: Some(context),
             })),
             srgb_capable,
         })
@@ -570,6 +587,43 @@ impl crate::Instance for Instance {
     }
 }
 
+impl super::Adapter {
+    /// Creates a new external adapter using the specified loader function.
+    ///
+    /// # Safety
+    ///
+    /// - The underlying OpenGL ES context must be current.
+    /// - The underlying OpenGL ES context must be current when interfacing with any objects returned by
+    ///   wgpu-hal from this adapter.
+    /// - The underlying OpenGL ES context must be current when dropping this adapter and when
+    ///   dropping any objects returned from this adapter.
+    pub unsafe fn new_external(
+        fun: impl FnMut(&str) -> *const c_void,
+    ) -> Option<crate::ExposedAdapter<super::Api>> {
+        let context = unsafe { glow::Context::from_loader_function(fun) };
+        unsafe {
+            Self::expose(AdapterContext {
+                inner: Arc::new(Mutex::new(Inner {
+                    gl: ManuallyDrop::new(context),
+                    device: create_instance_device().ok()?,
+                    context: None,
+                })),
+            })
+        }
+    }
+
+    pub fn adapter_context(&self) -> &AdapterContext {
+        &self.shared.context
+    }
+}
+
+impl super::Device {
+    /// Returns the underlying WGL context.
+    pub fn context(&self) -> &AdapterContext {
+        &self.shared.context
+    }
+}
+
 struct DeviceContextHandle {
     device: Gdi::HDC,
     window: Foundation::HWND,