Merge pull request #480 from Smithay/fix/winit_buffer_age

winit: Fix returned buffer age

src/backend/egl/surface.rs

@@ -81,18 +81,28 @@ impl EGLSurface {
     }
 
     /// Returns the buffer age of the underlying back buffer
-    pub fn buffer_age(&self) -> i32 {
+    pub fn buffer_age(&self) -> Option<i32> {
         let surface = self.surface.load(Ordering::SeqCst);
         let mut age = 0;
-        unsafe {
+        let ret = unsafe {
             ffi::egl::QuerySurface(
                 **self.display,
                 surface as *const _,
                 ffi::egl::BUFFER_AGE_EXT as i32,
                 &mut age as *mut _,
+            )
+        };
+        if ret == ffi::egl::FALSE {
+            slog::debug!(
+                self.logger,
+                "Failed to query buffer age value for surface {:?}: {}",
+                self,
+                EGLError::from_last_call().unwrap_err()
             );
+            None
+        } else {
+            Some(age)
         }
-        age
     }
 
     /// Swaps buffers at the end of a frame.

src/backend/renderer/gles2/mod.rs

@@ -874,6 +874,7 @@ impl Bind<Rc<EGLSurface>> for Gles2Renderer {
     fn bind(&mut self, surface: Rc<EGLSurface>) -> Result<(), Gles2Error> {
         self.unbind()?;
         self.target_surface = Some(surface);
+        self.make_current()?;
         Ok(())
     }
 }
@@ -881,9 +882,7 @@ impl Bind<Rc<EGLSurface>> for Gles2Renderer {
 impl Bind<Dmabuf> for Gles2Renderer {
     fn bind(&mut self, dmabuf: Dmabuf) -> Result<(), Gles2Error> {
         self.unbind()?;
-        unsafe {
-            self.egl.make_current()?;
-        }
+        self.make_current()?;
 
         // Free outdated buffer resources
         // TODO: Replace with `drain_filter` once it lands

src/backend/winit/mod.rs

@@ -302,12 +302,19 @@ impl WinitGraphicsBackend {
         Ok(())
     }
 
-    /// Retrieve the buffer age of the current backbuffer of the window
-    pub fn buffer_age(&self) -> usize {
+    /// Retrieve the buffer age of the current backbuffer of the window.
+    ///
+    /// This will only return a meaningful value, if this `WinitGraphicsBackend`
+    /// is currently bound (by previously calling [`WinitGraphicsBackend::bind`]).
+    ///
+    /// Otherwise and on error this function returns `None`.
+    /// If you are using this value actively e.g. for damage-tracking you should
+    /// likely interpret an error just as if "0" was returned.
+    pub fn buffer_age(&self) -> Option<usize> {
         if self.damage_tracking {
-            self.egl.buffer_age() as usize
+            self.egl.buffer_age().map(|x| x as usize)
         } else {
-            0
+            Some(0)
         }
     }