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 637 matching lines @@
   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())
-    return BeginFrameNeededToAnimateOrDraw();
+    return (BeginFrameNeededToAnimateOrDraw() || BeginFrameNeededToChildren());

[brianderson, 2014/08/28 02:48:07]

This should not include BeginFrameNeededToChildren. In this if block, we should
DCHECK(!BeginFrameNeedeToChildren()) since the synchronous compositor doesn't
have a Browser.

If we ever need to support such a configuration we'd need to figure out a way to
send BeginFrames to children without triggering a Browser draw, which would get
complicated. Luckily, there are no plans to do support that config.

[simonhong, 2014/09/03 21:02:23]

Done.

 
-  return BeginFrameNeededToAnimateOrDraw() || ProactiveBeginFrameWanted();
+  return (BeginFrameNeededToAnimateOrDraw() ||
+          BeginFrameNeededToChildren() ||

[brianderson, 2014/08/28 02:48:07]

BeginFrameNeededToChildren belongs in ProactiveBeginFrameWanted since the
Browser might not draw immediately if the Renderer is slow.

[simonhong, 2014/09/03 21:02:23]

How Browser knows whether Renderer is slow or not in
ProactiveBeginFrameWanted()?
I think it only checks Browser-side scheduler status.

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

Nevermind about my comment here. What you have is good.

I wanted to think of children wanting BeginFrames as a proactive signal (and
have the logic equal to what you already have), but I think that was just me
trying to fit a new concept into an old way of thinking.

+          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) {
+  DCHECK(settings_.begin_frame_publisher && !settings_.begin_frame_receiver);
+  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