swapchain: Don't force release of submitted buffers

src/backend/allocator/swapchain.rs

@@ -154,11 +154,13 @@ where
     /// Mark a given buffer as submitted.
     ///
     /// This might effect internal data (e.g. buffer age) and may only be called,
-    /// if the buffer was actually used for display.
+    /// the buffer may not be used for rendering anymore.
+    /// You may hold on to it, if you require keeping it alive.
+    ///
     /// Buffers can always just be safely discarded by dropping them, but not
-    /// calling this function may affect performance characteristics
+    /// calling this function before may affect performance characteristics
     /// (e.g. by not tracking the buffer age).
-    pub fn submitted(&self, slot: Slot<B>) {
+    pub fn submitted(&self, slot: &Slot<B>) {
         // don't mess up the state, if the user submitted and old buffer, after e.g. a resize
         if !self.slots.iter().any(|other| Arc::ptr_eq(&slot.0, other)) {
             return;
@@ -167,7 +169,7 @@ where
         slot.0.age.store(1, Ordering::SeqCst);
         for other_slot in &self.slots {
             if !Arc::ptr_eq(other_slot, &slot.0) && other_slot.buffer.is_some() {
-                assert!(other_slot
+                let res = other_slot
                     .age
                     .fetch_update(Ordering::SeqCst, Ordering::SeqCst, |age| {
                         if age > 0 {
@@ -175,8 +177,8 @@ where
                         } else {
                             Some(0)
                         }
-                    })
-                    .is_ok());
+                    });
+                assert!(res.is_ok());
             }
         }
     }

src/backend/drm/surface/gbm.rs

@@ -213,7 +213,6 @@ where
     pub fn frame_submitted(&mut self) -> Result<(), Error> {
         if let Some(mut pending) = self.pending_fb.take() {
             std::mem::swap(&mut pending, &mut self.current_fb);
-            self.swapchain.submitted(pending);
             if self.queued_fb.is_some() {
                 self.submit()?;
             }
@@ -233,6 +232,7 @@ where
             self.drm.page_flip([(fb, self.drm.plane())].iter(), true)
         };
         if flip.is_ok() {
+            self.swapchain.submitted(&slot);
             self.pending_fb = Some(slot);
         }
         flip.map_err(Error::DrmError)

src/backend/x11/surface.rs

@@ -123,7 +123,7 @@ impl X11Surface {
 
             // Now present the current buffer
             let _ = pixmap.present(&*connection, window.as_ref())?;
-            self.swapchain.submitted(next);
+            self.swapchain.submitted(&next);
 
             // Flush the connection after presenting to the window to ensure we don't run out of buffer space in the X11 connection.
             let _ = connection.flush();