Unified BeginFrame scheduling

cc/scheduler/scheduler_state_machine.cc

 // Copyright 2011 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "cc/scheduler/scheduler_state_machine.h"
 
 #include "base/debug/trace_event.h"
 #include "base/debug/trace_event_argument.h"
 #include "base/format_macros.h"
 #include "base/logging.h"
@@ skipping 29 matching lines @@
       visible_(false),
       can_start_(false),
       can_draw_(false),
       has_pending_tree_(false),
       pending_tree_is_ready_for_activation_(false),
       active_tree_needs_first_draw_(false),
       did_create_and_initialize_first_output_surface_(false),
       smoothness_takes_priority_(false),
       skip_next_begin_main_frame_to_reduce_latency_(false),
       skip_begin_main_frame_to_reduce_latency_(false),
-      continuous_painting_(false) {
+      continuous_painting_(false),
+      children_need_begin_frames_(false) {
 }
 
 const char* SchedulerStateMachine::OutputSurfaceStateToString(
     OutputSurfaceState state) {
   switch (state) {
     case OUTPUT_SURFACE_ACTIVE:
       return "OUTPUT_SURFACE_ACTIVE";
     case OUTPUT_SURFACE_LOST:
       return "OUTPUT_SURFACE_LOST";
     case OUTPUT_SURFACE_CREATING:
@@ skipping 636 matching lines @@
 void SchedulerStateMachine::SetSkipNextBeginMainFrameToReduceLatency() {
   skip_next_begin_main_frame_to_reduce_latency_ = true;
 }
 
 bool SchedulerStateMachine::BeginFrameNeeded() const {
   // Proactive BeginFrames are bad for the synchronous compositor because we
   // have to draw when we get the BeginFrame and could end up drawing many
   // duplicate frames if our new frame isn't ready in time.
   // To poll for state with the synchronous compositor without having to draw,
   // we rely on ShouldPollForAnticipatedDrawTriggers instead.
-  if (!SupportsProactiveBeginFrame())
+  if (!SupportsProactiveBeginFrame()) {
+    DCHECK(!BeginFrameNeededToChildren());

[brianderson, 2014/09/04 18:45:46]

Can you add a comment regarding why we added this DCHECK?

     return BeginFrameNeededToAnimateOrDraw();
+  }
 
-  return BeginFrameNeededToAnimateOrDraw() || ProactiveBeginFrameWanted();
+  return (BeginFrameNeededToAnimateOrDraw() ||
+          BeginFrameNeededToChildren() ||
+          ProactiveBeginFrameWanted());
 }
 
 bool SchedulerStateMachine::ShouldPollForAnticipatedDrawTriggers() const {
   // ShouldPollForAnticipatedDrawTriggers is what we use in place of
   // ProactiveBeginFrameWanted when we are using the synchronous
   // compositor.
   if (!SupportsProactiveBeginFrame()) {
     return !BeginFrameNeededToAnimateOrDraw() && ProactiveBeginFrameWanted();
   }
 
   // Non synchronous compositors should rely on
   // ProactiveBeginFrameWanted to poll for state instead.
   return false;
 }
 
 // Note: If SupportsProactiveBeginFrame is false, the scheduler should poll
 // for changes in it's draw state so it can request a BeginFrame when it's
 // actually ready.
 bool SchedulerStateMachine::SupportsProactiveBeginFrame() const {
   // It is undesirable to proactively request BeginFrames if we are
   // using a synchronous compositor because we *must* draw for every
   // BeginFrame, which could cause duplicate draws.
   return !settings_.using_synchronous_renderer_compositor;
 }
 
+void SchedulerStateMachine::SetChildrenNeedBeginFrames(
+    bool children_need_begin_frames) {
+#if !defined(OS_ANDROID) && !defined(OS_MACOSX)

[brianderson, 2014/09/04 18:45:46]

We try to avoid platforms-specific defines in cc if possible.
Maybe just DCHECK(settings_.begin_frame_publisher) for all platforms?

+  DCHECK(settings_.begin_frame_publisher && !settings_.begin_frame_receiver);
+#endif
+  children_need_begin_frames_ = children_need_begin_frames;
+}
+
 // These are the cases where we definitely (or almost definitely) have a
 // new frame to animate and/or draw and can draw.
 bool SchedulerStateMachine::BeginFrameNeededToAnimateOrDraw() const {
   // The output surface is the provider of BeginImplFrames, so we are not going
   // to get them even if we ask for them.
   if (!HasInitializedOutputSurface())
     return false;
 
   // If we can't draw, don't tick until we are notified that we can draw again.
   if (!can_draw_)
@@ skipping 13 matching lines @@
   // additional visible tiles.
   if (swap_used_incomplete_tile_)
     return true;
 
   if (needs_animate_)
     return true;
 
   return needs_redraw_;
 }
 
+bool SchedulerStateMachine::BeginFrameNeededToChildren() const {
+  if (!HasInitializedOutputSurface())
+    return false;
+
+  // If we can't draw, don't tick until we are notified that we can draw again.
+  if (!can_draw_)
+    return false;
+
+  return children_need_begin_frames_;
+}
+
 // These are cases where we are very likely to draw soon, but might not
 // actually have a new frame to draw when we receive the next BeginImplFrame.
 // Proactively requesting the BeginImplFrame helps hide the round trip latency
 // of the SetNeedsBeginFrame request that has to go to the Browser.
 bool SchedulerStateMachine::ProactiveBeginFrameWanted() const {
   // The output surface is the provider of BeginImplFrames,
   // so we are not going to get them even if we ask for them.
   if (!HasInitializedOutputSurface())
     return false;
 
@@ skipping 294 matching lines @@
     case OUTPUT_SURFACE_ACTIVE:
     case OUTPUT_SURFACE_WAITING_FOR_FIRST_COMMIT:
     case OUTPUT_SURFACE_WAITING_FOR_FIRST_ACTIVATION:
       return true;
   }
   NOTREACHED();
   return false;
 }
 
 }  // namespace cc