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 <memory>
#include <string>

#include "base/macros.h"
#include "cc/base/cc_export.h"
#include "cc/output/begin_frame_args.h"
#include "cc/scheduler/commit_earlyout_reason.h"
#include "cc/scheduler/draw_result.h"
#include "cc/scheduler/scheduler_settings.h"
#include "cc/tiles/tile_priority.h"

namespace base {
namespace trace_event {
class ConvertableToTraceFormat;
class TracedValue;
}
class Value;
}

namespace cc {

enum class ScrollHandlerState {
  SCROLL_AFFECTS_SCROLL_HANDLER,
  SCROLL_DOES_NOT_AFFECT_SCROLL_HANDLER,
};
const char* ScrollHandlerStateToString(ScrollHandlerState state);

// The SchedulerStateMachine decides how to coordinate main thread activites
// like painting/running javascript with rendering and input activities on the
// impl thread.
//
// The state machine tracks internal state but is also influenced by external
// state.  Internal state includes things like whether a frame has been
// requested, while external state includes things like the current time being
// near to the vblank time.
//
// The scheduler seperates "what to do next" from the updating of its internal
// state to make testing cleaner.
class CC_EXPORT SchedulerStateMachine {
 public:
  // settings must be valid for the lifetime of this class.
  explicit SchedulerStateMachine(const SchedulerSettings& settings);

  enum OutputSurfaceState {
    OUTPUT_SURFACE_NONE,
    OUTPUT_SURFACE_ACTIVE,
    OUTPUT_SURFACE_CREATING,
    OUTPUT_SURFACE_WAITING_FOR_FIRST_COMMIT,
    OUTPUT_SURFACE_WAITING_FOR_FIRST_ACTIVATION,
  };
  static const char* OutputSurfaceStateToString(OutputSurfaceState state);

  // Note: BeginImplFrameState does not cycle through these states in a fixed
  // order on all platforms. It's up to the scheduler to set these correctly.
  enum BeginImplFrameState {
    BEGIN_IMPL_FRAME_STATE_IDLE,
    BEGIN_IMPL_FRAME_STATE_INSIDE_BEGIN_FRAME,
    BEGIN_IMPL_FRAME_STATE_INSIDE_DEADLINE,
  };
  static const char* BeginImplFrameStateToString(BeginImplFrameState state);

  enum BeginImplFrameDeadlineMode {
    BEGIN_IMPL_FRAME_DEADLINE_MODE_NONE,
    BEGIN_IMPL_FRAME_DEADLINE_MODE_IMMEDIATE,
    BEGIN_IMPL_FRAME_DEADLINE_MODE_REGULAR,
    BEGIN_IMPL_FRAME_DEADLINE_MODE_LATE,
    BEGIN_IMPL_FRAME_DEADLINE_MODE_BLOCKED_ON_READY_TO_DRAW,
  };
  static const char* BeginImplFrameDeadlineModeToString(
      BeginImplFrameDeadlineMode mode);

  enum BeginMainFrameState {
    BEGIN_MAIN_FRAME_STATE_IDLE,
    BEGIN_MAIN_FRAME_STATE_SENT,
    BEGIN_MAIN_FRAME_STATE_STARTED,
    BEGIN_MAIN_FRAME_STATE_READY_TO_COMMIT,
    BEGIN_MAIN_FRAME_STATE_WAITING_FOR_ACTIVATION,
    BEGIN_MAIN_FRAME_STATE_WAITING_FOR_DRAW,
  };
  static const char* BeginMainFrameStateToString(BeginMainFrameState state);

  enum ForcedRedrawOnTimeoutState {
    FORCED_REDRAW_STATE_IDLE,
    FORCED_REDRAW_STATE_WAITING_FOR_COMMIT,
    FORCED_REDRAW_STATE_WAITING_FOR_ACTIVATION,
    FORCED_REDRAW_STATE_WAITING_FOR_DRAW,
  };
  static const char* ForcedRedrawOnTimeoutStateToString(
      ForcedRedrawOnTimeoutState state);

  BeginMainFrameState begin_main_frame_state() const {
    return begin_main_frame_state_;
  }

  bool CommitPending() const {
    return begin_main_frame_state_ == BEGIN_MAIN_FRAME_STATE_SENT ||
           begin_main_frame_state_ == BEGIN_MAIN_FRAME_STATE_STARTED ||
           begin_main_frame_state_ == BEGIN_MAIN_FRAME_STATE_READY_TO_COMMIT;
  }

  bool NewActiveTreeLikely() const {
    return needs_begin_main_frame_ || CommitPending() || has_pending_tree_;
  }

  bool RedrawPending() const { return needs_redraw_; }
  bool PrepareTilesPending() const { return needs_prepare_tiles_; }

  enum Action {
    ACTION_NONE,
    ACTION_SEND_BEGIN_MAIN_FRAME,
    ACTION_COMMIT,
    ACTION_ACTIVATE_SYNC_TREE,
    ACTION_DRAW_AND_SWAP_IF_POSSIBLE,
    ACTION_DRAW_AND_SWAP_FORCED,
    ACTION_DRAW_AND_SWAP_ABORT,
    ACTION_BEGIN_OUTPUT_SURFACE_CREATION,
    ACTION_PREPARE_TILES,
    ACTION_INVALIDATE_OUTPUT_SURFACE,
  };
  static const char* ActionToString(Action action);

  std::unique_ptr<base::trace_event::ConvertableToTraceFormat> AsValue() const;
  void AsValueInto(base::trace_event::TracedValue* dict) const;

  Action NextAction() const;
  void WillSendBeginMainFrame();
  void WillCommit(bool commit_had_no_updates);
  void WillActivate();
  void WillDraw();
  void WillBeginOutputSurfaceCreation();
  void WillPrepareTiles();
  void WillInvalidateOutputSurface();

  void DidDraw(DrawResult draw_result);

  void AbortDrawAndSwap();

  // Indicates whether the impl thread needs a BeginImplFrame callback in order
  // to make progress.
  bool BeginFrameNeeded() const;

  // Indicates that the system has entered and left a BeginImplFrame callback.
  // The scheduler will not draw more than once in a given BeginImplFrame
  // callback nor send more than one BeginMainFrame message.
  void OnBeginImplFrame();
  // Indicates that the scheduler has entered the draw phase. The scheduler
  // will not draw more than once in a single draw phase.
  // TODO(sunnyps): Rename OnBeginImplFrameDeadline to OnDraw or similar.
  void OnBeginImplFrameDeadline();
  void OnBeginImplFrameIdle();
  BeginImplFrameState begin_impl_frame_state() const {
    return begin_impl_frame_state_;
  }
  BeginImplFrameDeadlineMode CurrentBeginImplFrameDeadlineMode() const;

  // If the main thread didn't manage to produce a new frame in time for the
  // impl thread to draw, it is in a high latency mode.
  bool main_thread_missed_last_deadline() const {
    return main_thread_missed_last_deadline_;
  }

  bool SwapThrottled() const;

  // Indicates whether the LayerTreeHostImpl is visible.
  void SetVisible(bool visible);
  bool visible() const { return visible_; }

  void SetBeginFrameSourcePaused(bool paused);
  bool begin_frame_source_paused() const { return begin_frame_source_paused_; }

  // 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_; }

  bool OnlyImplSideUpdatesExpected() const;

  // Indicates that prepare-tiles is required. This guarantees another
  // PrepareTiles will occur shortly (even if no redraw is required).
  void SetNeedsPrepareTiles();

  // If the scheduler attempted to draw and swap, this provides feedback
  // regarding whether or not the swap actually occured. We might skip the
  // 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();

  int pending_swaps() const { return pending_swaps_; }

  // Indicates whether to prioritize impl thread latency (i.e., animation
  // smoothness) over new content activation.
  void SetTreePrioritiesAndScrollState(TreePriority tree_priority,
                                       ScrollHandlerState scroll_handler_state);

  // Indicates if the main thread will likely respond within 1 vsync.
  void SetCriticalBeginMainFrameToActivateIsFast(bool is_fast);

  // A function of SetTreePrioritiesAndScrollState and
  // SetCriticalBeginMainFrameToActivateIsFast.
  bool ImplLatencyTakesPriority() const;

  // Indicates that a new begin main frame flow needs to be performed, either
  // to pull updates from the main thread to the impl, or to push deltas from
  // the impl thread to main.
  void SetNeedsBeginMainFrame();
  bool needs_begin_main_frame() const { return needs_begin_main_frame_; }

  // Requests a single impl frame (after the current frame if there is one
  // active).
  void SetNeedsOneBeginImplFrame();

  // Call this only in response to receiving an ACTION_SEND_BEGIN_MAIN_FRAME
  // from NextAction.
  // Indicates that all painting is complete.
  void NotifyReadyToCommit();

  // Call this only in response to receiving an ACTION_SEND_BEGIN_MAIN_FRAME
  // from NextAction if the client rejects the BeginMainFrame message.
  void BeginMainFrameAborted(CommitEarlyOutReason reason);

  // Indicates production should be skipped to recover latency.
  void SetSkipNextBeginMainFrameToReduceLatency();

  // Resourceless software draws are allowed even when invisible.
  void SetResourcelessSoftwareDraw(bool resourceless_draw);

  // Indicates whether drawing would, at this time, make sense.
  // CanDraw can be used to suppress flashes or checkerboarding
  // when such behavior would be undesirable.
  void SetCanDraw(bool can);

  // Indicates that scheduled BeginMainFrame is started.
  void NotifyBeginMainFrameStarted();

  // Indicates that the pending tree is ready for activation.
  void NotifyReadyToActivate();

  // Indicates the active tree's visible tiles are ready to be drawn.
  void NotifyReadyToDraw();

  bool has_pending_tree() const { return has_pending_tree_; }
  bool active_tree_needs_first_draw() const {
    return active_tree_needs_first_draw_;
  }

  void DidPrepareTiles();
  void DidLoseOutputSurface();
  void DidCreateAndInitializeOutputSurface();
  bool HasInitializedOutputSurface() const;

  // True if we need to abort draws to make forward progress.
  bool PendingDrawsShouldBeAborted() const;

  bool CouldSendBeginMainFrame() const;

  void SetDeferCommits(bool defer_commits);

  void SetVideoNeedsBeginFrames(bool video_needs_begin_frames);
  bool video_needs_begin_frames() const { return video_needs_begin_frames_; }

 protected:
  bool BeginFrameRequiredForAction() const;
  bool BeginFrameNeededForVideo() const;
  bool ProactiveBeginFrameWanted() const;

  bool ShouldTriggerBeginImplFrameDeadlineImmediately() const;

  // True if we need to force activations to make forward progress.
  // TODO(sunnyps): Rename this to ShouldAbortCurrentFrame or similar.
  bool PendingActivationsShouldBeForced() const;

  bool ShouldBeginOutputSurfaceCreation() const;
  bool ShouldDraw() const;
  bool ShouldActivatePendingTree() const;
  bool ShouldSendBeginMainFrame() const;
  bool ShouldCommit() const;
  bool ShouldPrepareTiles() const;
  bool ShouldInvalidateOutputSurface() const;

  void WillDrawInternal();
  void DidDrawInternal(DrawResult draw_result);

  const SchedulerSettings settings_;

  OutputSurfaceState output_surface_state_;
  BeginImplFrameState begin_impl_frame_state_;
  BeginMainFrameState begin_main_frame_state_;
  ForcedRedrawOnTimeoutState forced_redraw_state_;

  // These are used for tracing only.
  int commit_count_;
  int current_frame_number_;
  int last_frame_number_swap_performed_;
  int last_frame_number_draw_performed_;
  int last_frame_number_begin_main_frame_sent_;
  int last_frame_number_invalidate_output_surface_performed_;

  // These are used to ensure that an action only happens once per frame,
  // deadline, etc.
  bool draw_funnel_;
  bool send_begin_main_frame_funnel_;
  bool invalidate_output_surface_funnel_;
  // prepare_tiles_funnel_ is "filled" each time PrepareTiles is called
  // and "drained" on each BeginImplFrame. If the funnel gets too full,
  // we start throttling ACTION_PREPARE_TILES such that we average one
  // PrepareTiles per BeginImplFrame.
  int prepare_tiles_funnel_;

  int consecutive_checkerboard_animations_;
  int max_pending_swaps_;
  int pending_swaps_;
  int swaps_with_current_output_surface_;
  bool needs_redraw_;
  bool needs_prepare_tiles_;
  bool needs_begin_main_frame_;
  bool needs_one_begin_impl_frame_;
  bool visible_;
  bool begin_frame_source_paused_;
  bool resourceless_draw_;
  bool can_draw_;
  bool has_pending_tree_;
  bool pending_tree_is_ready_for_activation_;
  bool active_tree_needs_first_draw_;
  bool did_create_and_initialize_first_output_surface_;
  TreePriority tree_priority_;
  ScrollHandlerState scroll_handler_state_;
  bool critical_begin_main_frame_to_activate_is_fast_;
  bool main_thread_missed_last_deadline_;
  bool skip_next_begin_main_frame_to_reduce_latency_;
  bool defer_commits_;
  bool video_needs_begin_frames_;
  bool last_commit_had_no_updates_;
  bool wait_for_ready_to_draw_;
  bool did_draw_in_last_frame_;
  bool did_swap_in_last_frame_;

 private:
  DISALLOW_COPY_AND_ASSIGN(SchedulerStateMachine);
};

}  // namespace cc

#endif  // CC_SCHEDULER_SCHEDULER_STATE_MACHINE_H_