exo: Connect frame callbacks with UI compositor begin frames.

components/exo/wayland/clients/motion_events.cc

Index: components/exo/wayland/clients/motion_events.cc
diff --git a/components/exo/wayland/clients/motion_events.cc b/components/exo/wayland/clients/motion_events.cc
index a55b6cd1971a61cceac43768127d2926203620a6..99e38eba2b79c3ddac9e12daf2ca9fc85fdb2ec3 100644
--- a/components/exo/wayland/clients/motion_events.cc
+++ b/components/exo/wayland/clients/motion_events.cc
@@ -34,6 +34,7 @@ DEFAULT_DELETER(wl_shell_surface, wl_shell_surface_destroy)
 DEFAULT_DELETER(wl_seat, wl_seat_destroy)
 DEFAULT_DELETER(wl_pointer, wl_pointer_destroy)
 DEFAULT_DELETER(wl_touch, wl_touch_destroy)
+DEFAULT_DELETER(wl_callback, wl_callback_destroy)
 
 namespace exo {
 namespace wayland {
@@ -105,6 +106,7 @@ struct MainLoopContext {
   uint32_t color = 0xffffffff;
   bool needs_redraw = true;
   bool shutdown = false;
+  bool throttled = false;
 };
 
 void PointerEnter(void* data,
@@ -195,6 +197,12 @@ void TouchFrame(void* data, wl_touch* touch) {}
 
 void TouchCancel(void* data, wl_touch* touch) {}
 
+void FrameCallback(void* data, wl_callback* callback, uint32_t time) {
+  MainLoopContext* context = static_cast<MainLoopContext*>(data);
+
+  context->throttled = false;
+}
+
 }  // namespace
 
 int MotionEventsMain() {
@@ -305,6 +313,9 @@ int MotionEventsMain() {
                                       TouchFrame, TouchCancel};
   wl_touch_add_listener(touch.get(), &touch_listener, &context);
 
+  std::unique_ptr<wl_callback> frame_callback;
+  wl_callback_listener frame_listener = {FrameCallback};
+
   do {
     if (context.shutdown)
       break;
@@ -312,6 +323,9 @@ int MotionEventsMain() {
     if (!context.needs_redraw)
       continue;
 
+    if (context.throttled)
+      continue;
+
     BufferState* buffer =
         std::find_if(std::begin(buffers), std::end(buffers),
                      [](const BufferState& buffer) { return !buffer.busy; });
@@ -331,6 +345,10 @@ int MotionEventsMain() {
     wl_surface_attach(surface.get(), buffer->buffer.get(), 0, 0);
     buffer->busy = true;
 
+    frame_callback.reset(wl_surface_frame(surface.get()));
+    wl_callback_add_listener(frame_callback.get(), &frame_listener, &context);
+    context.throttled = true;
+
     wl_surface_commit(surface.get());
     wl_display_flush(display.get());
   } while (wl_display_dispatch(display.get()) != -1);