make the frame_callback a list

anvil/src/shell.rs

@@ -677,7 +677,7 @@ pub struct CommitedState {
     pub buffer: Option<wl_buffer::WlBuffer>,
     pub input_region: Option<RegionAttributes>,
     pub dimensions: Option<(i32, i32)>,
-    pub frame_callback: Option<wl_callback::WlCallback>,
+    pub frame_callbacks: Vec<wl_callback::WlCallback>,
     pub sub_location: (i32, i32),
 }
 
@@ -734,12 +734,6 @@ impl SurfaceData {
                 buffer.release();
             }
         }
-        // ping the previous callback if relevant
-        if into.frame_callback != next.frame_callback {
-            if let Some(callback) = into.frame_callback.take() {
-                callback.done(0);
-            }
-        }
 
         *into = next;
         new_buffer
@@ -784,7 +778,7 @@ impl SurfaceData {
 
     /// Send the frame callback if it had been requested
     pub fn send_frame(&mut self, time: u32) {
-        if let Some(callback) = self.current_state.frame_callback.take() {
+        for callback in self.current_state.frame_callbacks.drain(..) {
             callback.done(time);
         }
     }
@@ -863,12 +857,10 @@ fn surface_commit(
             None => {}
         }
 
-        if let Some(frame_cb) = attributes.frame_callback.take() {
-            if let Some(old_cb) = next_state.frame_callback.take() {
-                old_cb.done(0);
-            }
-            next_state.frame_callback = Some(frame_cb);
-        }
+        // Append the current frame callbacks to the next state
+        next_state
+            .frame_callbacks
+            .extend(attributes.frame_callbacks.drain(..));
 
         data.apply_cache(next_state);
 

src/wayland/compositor/handlers.rs

@@ -83,7 +83,7 @@ where
             }
             wl_surface::Request::Frame { callback } => {
                 SurfaceData::<R>::with_data(&surface, move |d| {
-                    d.frame_callback = Some((*callback).clone());
+                    d.frame_callbacks.push((*callback).clone());
                 });
             }
             wl_surface::Request::SetOpaqueRegion { region } => {

src/wayland/compositor/mod.rs

@@ -156,14 +156,22 @@ pub struct SurfaceAttributes {
     /// Hint provided by the client to suggest that only this part
     /// of the surface was changed and needs to be redrawn
     pub damage: Vec<Damage>,
-    /// The frame callback associated with this surface for the commit
+    /// The frame callbacks associated with this surface for the commit
     ///
-    /// The be triggered to notify the client about when it would be a
-    /// good time to start drawing its next frame.
+    /// The server must send the notifications so that a client
+    /// will not send excessive updates, while still allowing
+    /// the highest possible update rate for clients that wait for the reply
+    /// before drawing again. The server should give some time for the client
+    /// to draw and commit after sending the frame callback events to let it
+    /// hit the next output refresh.
+    ///
+    /// A server should avoid signaling the frame callbacks if the
+    /// surface is not visible in any way, e.g. the surface is off-screen,
+    /// or completely obscured by other opaque surfaces.
     ///
     /// An example possibility would be to trigger it once the frame
     /// associated with this commit has been displayed on the screen.
-    pub frame_callback: Option<wl_callback::WlCallback>,
+    pub frame_callbacks: Vec<wl_callback::WlCallback>,
     /// User-controlled data
     ///
     /// This is your field to host whatever you need.
@@ -180,7 +188,7 @@ impl fmt::Debug for SurfaceAttributes {
             .field("opaque_region", &self.opaque_region)
             .field("input_region", &self.input_region)
             .field("damage", &self.damage)
-            .field("frame_callback", &self.frame_callback)
+            .field("frame_callbacks", &self.frame_callbacks)
             .field("user_data", &"...")
             .finish()
     }
@@ -195,7 +203,7 @@ impl Default for SurfaceAttributes {
             opaque_region: None,
             input_region: None,
             damage: Vec::new(),
-            frame_callback: None,
+            frame_callbacks: Vec::new(),
             user_data: UserDataMap::new(),
         }
     }