Implement priority hints for EGL

CHANGELOG.md

@@ -3,6 +3,7 @@
 - Added `PossiblyCurrentContext::make_not_current_in_place(&self)` for when `Send` capability of `NotCurrentContext` is not required.
 - Added workaround for EGL drivers reporting `EGL_KHR_platform_gbm` without EGL 1.5 client.
 - **Breaking:** Added `make_current_surfaceless(self)` for `{Possibly,Not}CurrentGlContext`.
+- Added `GlContext::priority`/`ContextAttributesBuilder::with_priority` to get/set context priority.
 
 # Version 0.32.1
 

glutin/src/api/cgl/context.rs

@@ -10,7 +10,9 @@ use objc2_app_kit::{NSOpenGLCPSwapInterval, NSView};
 use objc2_foundation::{run_on_main, MainThreadBound};
 
 use crate::config::GetGlConfig;
-use crate::context::{AsRawContext, ContextApi, ContextAttributes, RawContext, Robustness};
+use crate::context::{
+    AsRawContext, ContextApi, ContextAttributes, Priority, RawContext, Robustness,
+};
 use crate::display::GetGlDisplay;
 use crate::error::{ErrorKind, Result};
 use crate::prelude::*;
@@ -113,6 +115,10 @@ impl GlContext for NotCurrentContext {
     fn context_api(&self) -> ContextApi {
         self.inner.context_api()
     }
+
+    fn priority(&self) -> Priority {
+        Priority::Medium
+    }
 }
 
 impl GetGlConfig for NotCurrentContext {
@@ -190,6 +196,10 @@ impl GlContext for PossiblyCurrentContext {
     fn context_api(&self) -> ContextApi {
         self.inner.context_api()
     }
+
+    fn priority(&self) -> Priority {
+        Priority::Medium
+    }
 }
 
 impl GetGlConfig for PossiblyCurrentContext {

glutin/src/api/egl/context.rs

@@ -9,7 +9,8 @@ use glutin_egl_sys::{egl, EGLContext};
 
 use crate::config::{Api, GetGlConfig};
 use crate::context::{
-    self, AsRawContext, ContextApi, ContextAttributes, GlProfile, RawContext, Robustness, Version,
+    self, AsRawContext, ContextApi, ContextAttributes, GlProfile, Priority, RawContext, Robustness,
+    Version,
 };
 use crate::display::{DisplayFeatures, GetGlDisplay};
 use crate::error::{ErrorKind, Result};
@@ -126,6 +127,38 @@ impl Display {
             }
         }
 
+        if let Some(priority) = context_attributes.priority.filter(|_| {
+            let extensions = &self.inner.display_extensions;
+
+            // Some android versions don't report support for this extension, even though
+            // it's supported.
+            //
+            // https://github.com/googlevr/gvr-android-sdk/issues/330
+            #[cfg(android_platform)]
+            let android = extensions.contains("EGL_ANDROID_front_buffer_auto_refresh")
+                && extensions.contains("EGL_ANDROID_create_native_client_buffer");
+            #[cfg(not(android_platform))]
+            let android = false;
+
+            extensions.contains("EGL_IMG_context_priority") || android
+        }) {
+            let priority = match priority {
+                Priority::Low => egl::CONTEXT_PRIORITY_LOW_IMG,
+                Priority::Medium => egl::CONTEXT_PRIORITY_MEDIUM_IMG,
+                Priority::High => egl::CONTEXT_PRIORITY_HIGH_IMG,
+                Priority::Realtime => {
+                    if self.inner.display_extensions.contains("EGL_NV_context_priority_realtime") {
+                        egl::CONTEXT_PRIORITY_REALTIME_NV
+                    } else {
+                        egl::CONTEXT_PRIORITY_HIGH_IMG
+                    }
+                },
+            };
+
+            attrs.push(egl::CONTEXT_PRIORITY_LEVEL_IMG as EGLint);
+            attrs.push(priority as EGLint);
+        }
+
         attrs.push(egl::NONE as EGLint);
 
         let shared_context = if let Some(shared_context) =
@@ -212,6 +245,10 @@ impl GlContext for NotCurrentContext {
     fn context_api(&self) -> ContextApi {
         self.inner.context_api()
     }
+
+    fn priority(&self) -> Priority {
+        self.inner.priority()
+    }
 }
 
 impl GetGlConfig for NotCurrentContext {
@@ -286,6 +323,10 @@ impl GlContext for PossiblyCurrentContext {
     fn context_api(&self) -> ContextApi {
         self.inner.context_api()
     }
+
+    fn priority(&self) -> Priority {
+        self.inner.priority()
+    }
 }
 
 impl GetGlConfig for PossiblyCurrentContext {
@@ -380,6 +421,16 @@ impl ContextInner {
         }
     }
 
+    fn priority(&self) -> Priority {
+        match self.query_attribute(egl::CONTEXT_PRIORITY_LEVEL_IMG as EGLint).map(|a| a as EGLenum)
+        {
+            Some(egl::CONTEXT_PRIORITY_LOW_IMG) => Priority::Low,
+            Some(egl::CONTEXT_PRIORITY_HIGH_IMG) => Priority::High,
+            Some(egl::CONTEXT_PRIORITY_REALTIME_NV) => Priority::Realtime,
+            _ => Priority::Medium,
+        }
+    }
+
     /// Query the context attribute.
     fn query_attribute(&self, attribute: EGLint) -> Option<EGLint> {
         unsafe {

glutin/src/api/glx/context.rs

@@ -10,8 +10,8 @@ use glutin_glx_sys::{glx, glx_extra};
 
 use crate::config::GetGlConfig;
 use crate::context::{
-    self, AsRawContext, ContextApi, ContextAttributes, GlProfile, RawContext, ReleaseBehavior,
-    Robustness, Version,
+    self, AsRawContext, ContextApi, ContextAttributes, GlProfile, Priority, RawContext,
+    ReleaseBehavior, Robustness, Version,
 };
 use crate::display::{DisplayFeatures, GetGlDisplay};
 use crate::error::{ErrorKind, Result};
@@ -281,6 +281,10 @@ impl GlContext for NotCurrentContext {
     fn context_api(&self) -> ContextApi {
         self.inner.context_api()
     }
+
+    fn priority(&self) -> Priority {
+        Priority::Medium
+    }
 }
 
 impl GetGlConfig for NotCurrentContext {
@@ -353,6 +357,10 @@ impl GlContext for PossiblyCurrentContext {
     fn context_api(&self) -> ContextApi {
         self.inner.context_api()
     }
+
+    fn priority(&self) -> Priority {
+        Priority::Medium
+    }
 }
 
 impl GetGlConfig for PossiblyCurrentContext {

glutin/src/api/wgl/context.rs

@@ -13,8 +13,8 @@ use windows_sys::Win32::Graphics::Gdi::{self as gdi, HDC};
 
 use crate::config::GetGlConfig;
 use crate::context::{
-    self, AsRawContext, ContextApi, ContextAttributes, GlProfile, RawContext, ReleaseBehavior,
-    Robustness, Version,
+    self, AsRawContext, ContextApi, ContextAttributes, GlProfile, Priority, RawContext,
+    ReleaseBehavior, Robustness, Version,
 };
 use crate::display::{DisplayFeatures, GetGlDisplay};
 use crate::error::{ErrorKind, Result};
@@ -268,6 +268,10 @@ impl GlContext for NotCurrentContext {
     fn context_api(&self) -> ContextApi {
         self.inner.context_api()
     }
+
+    fn priority(&self) -> Priority {
+        Priority::Medium
+    }
 }
 
 impl GetGlDisplay for NotCurrentContext {
@@ -364,6 +368,10 @@ impl GlContext for PossiblyCurrentContext {
     fn context_api(&self) -> ContextApi {
         self.inner.context_api()
     }
+
+    fn priority(&self) -> Priority {
+        Priority::Medium
+    }
 }
 
 impl AsRawContext for PossiblyCurrentContext {

glutin/src/context.rs

@@ -34,6 +34,9 @@ pub trait GlContext: Sealed {
     ///
     /// The returned value's [`Version`] will always be `None`.
     fn context_api(&self) -> ContextApi;
+
+    /// Get the [`Priority`] used by the context.
+    fn priority(&self) -> Priority;
 }
 
 /// A trait to group common not current operations.
@@ -224,6 +227,24 @@ impl ContextAttributesBuilder {
         self
     }
 
+    /// Set the priority hint, which might not be honored if the API does not
+    /// support it, if there are constraints on the number of high priority
+    /// contexts available in the system, or system policy limits access to
+    /// high priority contexts to appropriate system privilege level the
+    /// context creation may fail.
+    ///
+    /// By default no priority is specified, which corresponds to
+    /// [`Priority::Medium`].
+    ///
+    /// # Api specific
+    ///
+    /// - **WGL/GLX:** not implemented.
+    /// - **CGL:** not supported.
+    pub fn with_priority(mut self, priority: Priority) -> Self {
+        self.attributes.priority = Some(priority);
+        self
+    }
+
     /// Build the context attributes.
     ///
     /// The `raw_window_handle` isn't required and here for WGL compatibility.
@@ -251,6 +272,8 @@ pub struct ContextAttributes {
 
     pub(crate) api: Option<ContextApi>,
 
+    pub(crate) priority: Option<Priority>,
+
     pub(crate) shared_context: Option<RawContext>,
 
     pub(crate) raw_window_handle: Option<RawWindowHandle>,
@@ -471,6 +494,10 @@ impl GlContext for NotCurrentContext {
     fn context_api(&self) -> ContextApi {
         gl_api_dispatch!(self; Self(context) => context.context_api())
     }
+
+    fn priority(&self) -> Priority {
+        gl_api_dispatch!(self; Self(context) => context.priority())
+    }
 }
 
 impl GetGlConfig for NotCurrentContext {
@@ -599,6 +626,10 @@ impl GlContext for PossiblyCurrentContext {
     fn context_api(&self) -> ContextApi {
         gl_api_dispatch!(self; Self(context) => context.context_api())
     }
+
+    fn priority(&self) -> Priority {
+        gl_api_dispatch!(self; Self(context) => context.priority())
+    }
 }
 
 impl GetGlConfig for PossiblyCurrentContext {
@@ -645,6 +676,25 @@ pub enum RawContext {
     Cgl(*const ffi::c_void),
 }
 
+/// Priority hint
+#[derive(Debug, Copy, Clone, PartialEq, Eq, Default)]
+pub enum Priority {
+    /// Lowest priority, contexts using this priority give way for most other
+    /// contexts.
+    Low,
+    /// Default priority.
+    #[default]
+    Medium,
+    /// High priority is usually required for VR applications.
+    High,
+    /// Realtime priority contexts are executed immediately and preempt any
+    /// current context running.
+    ///
+    /// When such context is not supported, [`Priority::High`] will be requested
+    /// instead.
+    Realtime,
+}
+
 /// Pick `GlProfile` and `Version` based on the provided params.
 #[cfg(any(egl_backend, glx_backend, wgl_backend))]
 pub(crate) fn pick_profile(

glutin_egl_sys/build.rs

@@ -35,6 +35,7 @@ fn main() {
             "EGL_EXT_platform_wayland",
             "EGL_EXT_platform_x11",
             "EGL_EXT_swap_buffers_with_damage",
+            "EGL_IMG_context_priority",
             "EGL_KHR_create_context",
             "EGL_KHR_create_context_no_error",
             "EGL_KHR_display_reference",
@@ -47,6 +48,7 @@ fn main() {
             "EGL_KHR_swap_buffers_with_damage",
             "EGL_KHR_wait_sync",
             "EGL_MESA_platform_gbm",
+            "EGL_NV_context_priority_realtime",
         ]);
 
         if target.contains("ios") {