wl_surface: dispatch frame requests from vblank event handlers

src/tree/output.rs

@@ -81,6 +81,7 @@ pub struct OutputNode {
     pub title_visible: Cell<bool>,
     pub schedule: Rc<OutputSchedule>,
     pub latch_event: EventSource<dyn LatchListener>,
+    pub vblank_event: EventSource<dyn VblankListener>,
     pub presentation_event: EventSource<dyn PresentationListener>,
 }
 
@@ -88,6 +89,10 @@ pub trait LatchListener {
     fn after_latch(self: Rc<Self>);
 }
 
+pub trait VblankListener {
+    fn after_vblank(self: Rc<Self>);
+}
+
 pub trait PresentationListener {
     fn presented(
         self: Rc<Self>,
@@ -126,6 +131,12 @@ impl OutputNode {
         }
     }
 
+    pub fn vblank(&self) {
+        for listener in self.vblank_event.iter() {
+            listener.after_vblank();
+        }
+    }
+
     pub fn presented(&self, tv_sec: u64, tv_nsec: u32, refresh: u32, seq: u64, flags: u32) {
         for listener in self.presentation_event.iter() {
             listener.presented(self, tv_sec, tv_nsec, refresh, seq, flags);