cc: Throttle swaps in Scheduler instead of OutputSurface

cc/scheduler/scheduler_state_machine.h

 // 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.
 
 #ifndef CC_SCHEDULER_SCHEDULER_STATE_MACHINE_H_
 #define CC_SCHEDULER_SCHEDULER_STATE_MACHINE_H_
 
 #include <string>
 
 #include "base/basictypes.h"
@@ skipping 150 matching lines @@
 
   // Indicates that a redraw is required, either due to the impl tree changing
   // or the screen being damaged and simply needing redisplay.
   void SetNeedsRedraw();
   bool needs_redraw() const { return needs_redraw_; }
 
   // Indicates that manage-tiles is required. This guarantees another
   // ManageTiles will occur shortly (even if no redraw is required).
   void SetNeedsManageTiles();
 
+  // Sets how many swaps can be pending to the OutputSurface.
+  void SetMaxSwapsPending(int max);
+
+  // If the scheduler attempted to draw and swap, this provides feedback
+  // regarding whether or not the swap actually occured. We might skip the

[danakj, 2014/04/11 15:12:28]

This overlaps with the DrawSwapReadbackResult::did_swap. Are you planning to
remove one of them? Why do we need both?

[brianderson, 2014/04/11 20:49:40]

Hmm, I was under the impression DrawSwapReadbackResult::did_swap would be true
even if there was no damage and we didn't end up swapping. That's only true for
the did_swap in SchedulerStateMachine::UpdateStateOnDraw(bool did_swap) though.

DidSwapBuffers is used for OutputSurface throttling and reflects whether or not
we actually swapped and should expect a swap ack. I'm not sure if there are any
other early outs other than the damage. I guess I early out on is_lost_, so
that's one difference in this patch.

How about I rename the did_swaps to did_request_swap?

[danakj, 2014/04/14 18:14:50]

The did_swap result is being dropped right now in
Scheduler::DrawAndSwapIfPossible() and Scheduler::DrawAndSwapForced().

What if those methods called back to the scheduler with the full
DrawSwapReadbackResult?

Right now the did_swap value seems only useful for the
Scheduler::DrawAndReadback() DCHECK on it.

Since we already have this data, it'd be nice to reuse it, or base the DCHECK on
the new mechanism and remove did_swap entirely?

+  // swap when there is not damage, for example.
+  void DidSwapBuffers();
+
   // Indicates whether a redraw is required because we are currently rendering
   // with a low resolution or checkerboarded tile.
   void SetSwapUsedIncompleteTile(bool used_incomplete_tile);
 
+  // Notification from the OutputSurface that a swap has been consumed.
+  void DidSwapBuffersComplete();
+
   // Indicates whether to prioritize animation smoothness over new content
   // activation.
   void SetSmoothnessTakesPriority(bool smoothness_takes_priority);
   bool smoothness_takes_priority() const { return smoothness_takes_priority_; }
 
   // Indicates whether ACTION_DRAW_AND_SWAP_IF_POSSIBLE drew to the screen.
   void DidDrawIfPossibleCompleted(DrawSwapReadbackResult::DrawResult result);
 
   // Indicates that a new commit flow needs to be performed, either to pull
   // updates from the main thread to the impl, or to push deltas from the impl
@@ skipping 93 matching lines @@
   int last_frame_number_swap_performed_;
   int last_frame_number_begin_main_frame_sent_;
   int last_frame_number_update_visible_tiles_was_called_;
 
   // manage_tiles_funnel_ is "filled" each time ManageTiles is called
   // and "drained" on each BeginImplFrame. If the funnel gets too full,
   // we start throttling ACTION_MANAGE_TILES such that we average one
   // ManageTile per BeginImplFrame.
   int manage_tiles_funnel_;
   int consecutive_checkerboard_animations_;
+  int max_pending_swaps_;
+  int pending_swaps_;
   bool needs_redraw_;
   bool needs_manage_tiles_;
   bool swap_used_incomplete_tile_;
   bool needs_commit_;
   bool inside_poll_for_anticipated_draw_triggers_;
   bool visible_;
   bool can_start_;
   bool can_draw_;
   bool has_pending_tree_;
   bool pending_tree_is_ready_for_activation_;
   bool active_tree_needs_first_draw_;
   bool draw_if_possible_failed_;
   bool did_create_and_initialize_first_output_surface_;
   bool smoothness_takes_priority_;
   bool skip_next_begin_main_frame_to_reduce_latency_;
   bool skip_begin_main_frame_to_reduce_latency_;
   bool continuous_painting_;
   bool needs_back_to_back_readback_;
 
  private:
   DISALLOW_COPY_AND_ASSIGN(SchedulerStateMachine);
 };
 
 }  // namespace cc
 
 #endif  // CC_SCHEDULER_SCHEDULER_STATE_MACHINE_H_