cc: Use BeginFrameArgs

cc/scheduler/scheduler_state_machine.cc

Index: cc/scheduler/scheduler_state_machine.cc
diff --git a/cc/scheduler/scheduler_state_machine.cc b/cc/scheduler/scheduler_state_machine.cc
index ed9c15f43f9d13af92e585dbf9ed58c608e99ecc..6c2d879ae1b769cbbd6f914d230f5ec69c235dab 100644
--- a/cc/scheduler/scheduler_state_machine.cc
+++ b/cc/scheduler/scheduler_state_machine.cc
@@ -12,54 +12,64 @@ namespace cc {
 
 SchedulerStateMachine::SchedulerStateMachine(const SchedulerSettings& settings)
     : settings_(settings),
+      output_surface_state_(OUTPUT_SURFACE_LOST),
+      begin_frame_state_(BEGIN_FRAME_STATE_IDLE),
       commit_state_(COMMIT_STATE_IDLE),
+      texture_state_(LAYER_TEXTURE_STATE_UNLOCKED),
+      readback_state_(READBACK_STATE_IDLE),
+      forced_redraw_state_(FORCED_REDRAW_STATE_IDLE),
       commit_count_(0),
-      current_frame_number_(0),
-      last_frame_number_where_begin_frame_sent_to_main_thread_(-1),
-      last_frame_number_where_draw_was_called_(-1),
-      last_frame_number_where_tree_activation_attempted_(-1),
-      last_frame_number_where_update_visible_tiles_was_called_(-1),
+      begin_frame_count_(0),
+      draw_attempt_count_(0),
+      last_begin_frame_count_draw_was_called_(-1),
+      last_draw_attempt_count_draw_was_called_(-1),
+      last_begin_frame_count_begin_frame_sent_to_main_thread_(-1),
+      last_draw_attempt_count_tree_activation_attempted_(-1),
+      last_draw_attempt_count_update_visible_tiles_was_called_(-1),
       consecutive_failed_draws_(0),
       maximum_number_of_failed_draws_before_draw_is_forced_(3),
       needs_redraw_(false),
       swap_used_incomplete_tile_(false),
-      needs_forced_redraw_(false),
-      needs_forced_redraw_after_next_commit_(false),
-      needs_redraw_after_next_commit_(false),
       needs_commit_(false),
-      needs_forced_commit_(false),
-      expect_immediate_begin_frame_for_main_thread_(false),
       main_thread_needs_layer_textures_(false),
-      inside_begin_frame_(false),
+      active_tree_has_been_drawn_(false),
+      active_tree_is_null_(true),
       visible_(false),
       can_start_(false),
       can_draw_(false),
       has_pending_tree_(false),
+      pending_tree_is_ready_for_activation_(false),
       draw_if_possible_failed_(false),
-      texture_state_(LAYER_TEXTURE_STATE_UNLOCKED),
-      output_surface_state_(OUTPUT_SURFACE_LOST),
       did_create_and_initialize_first_output_surface_(false) {}
 
 std::string SchedulerStateMachine::ToString() {
   std::string str;
-  base::StringAppendF(&str,
-                      "settings_.impl_side_painting = %d; ",
+  base::StringAppendF(&str, "settings_.impl_side_painting = %d; ",
                       settings_.impl_side_painting);
+  base::StringAppendF(&str, "output_surface_state_ = %d; ",
+                      output_surface_state_);
+  base::StringAppendF(&str, "begin_frame_state_ = %d; ", begin_frame_state_);
   base::StringAppendF(&str, "commit_state_ = %d; ", commit_state_);
+  base::StringAppendF(&str, "texture_state_ = %d; ", texture_state_);
+  base::StringAppendF(&str, "readback_state_ = %d; ", readback_state_);
+  base::StringAppendF(&str, "forced_redraw_state_ = %d; ",
+                      forced_redraw_state_);
   base::StringAppendF(&str, "commit_count_ = %d; ", commit_count_);
-  base::StringAppendF(
-      &str, "current_frame_number_ = %d; ", current_frame_number_);
+  base::StringAppendF(&str, "begin_frame_count_ = %d; ", begin_frame_count_);
+  base::StringAppendF(&str, "draw_attempt_count_ = %d; ", draw_attempt_count_);
+  base::StringAppendF(&str, "last_begin_frame_count_draw_was_called_ = %d; ",
+                      last_begin_frame_count_draw_was_called_);
+  base::StringAppendF(&str, "last_draw_attempt_count_draw_was_called_ = %d; ",
+                      last_draw_attempt_count_draw_was_called_);
   base::StringAppendF(&str,
-                      "last_frame_number_where_draw_was_called_ = %d; ",
-                      last_frame_number_where_draw_was_called_);
-  base::StringAppendF(
-      &str,
-      "last_frame_number_where_tree_activation_attempted_ = %d; ",
-      last_frame_number_where_tree_activation_attempted_);
-  base::StringAppendF(
-      &str,
-      "last_frame_number_where_update_visible_tiles_was_called_ = %d; ",
-      last_frame_number_where_update_visible_tiles_was_called_);
+      "last_begin_frame_count_begin_frame_sent_to_main_thread_ = %d; ",
+      last_begin_frame_count_begin_frame_sent_to_main_thread_);
+  base::StringAppendF(&str,
+      "last_draw_attempt_count_tree_activation_attempted_ = %d; ",
+      last_draw_attempt_count_tree_activation_attempted_);
+  base::StringAppendF(&str,
+      "last_draw_attempt_count_update_visible_tiles_was_called_ = %d; ",
+      last_draw_attempt_count_update_visible_tiles_was_called_);
   base::StringAppendF(
       &str, "consecutive_failed_draws_ = %d; ", consecutive_failed_draws_);
   base::StringAppendF(
@@ -69,22 +79,10 @@ std::string SchedulerStateMachine::ToString() {
   base::StringAppendF(&str, "needs_redraw_ = %d; ", needs_redraw_);
   base::StringAppendF(
       &str, "swap_used_incomplete_tile_ = %d; ", swap_used_incomplete_tile_);
-  base::StringAppendF(
-      &str, "needs_forced_redraw_ = %d; ", needs_forced_redraw_);
-  base::StringAppendF(&str,
-                      "needs_forced_redraw_after_next_commit_ = %d; ",
-                      needs_forced_redraw_after_next_commit_);
   base::StringAppendF(&str, "needs_commit_ = %d; ", needs_commit_);
-  base::StringAppendF(
-      &str, "needs_forced_commit_ = %d; ", needs_forced_commit_);
-  base::StringAppendF(&str,
-                      "expect_immediate_begin_frame_for_main_thread_ = %d; ",
-                      expect_immediate_begin_frame_for_main_thread_);
   base::StringAppendF(&str,
                       "main_thread_needs_layer_textures_ = %d; ",
                       main_thread_needs_layer_textures_);
-  base::StringAppendF(&str, "inside_begin_frame_ = %d; ",
-      inside_begin_frame_);
   base::StringAppendF(&str, "last_frame_time_ = %" PRId64 "; ",
       (last_begin_frame_args_.frame_time - base::TimeTicks())
           .InMilliseconds());
@@ -98,36 +96,89 @@ std::string SchedulerStateMachine::ToString() {
   base::StringAppendF(
       &str, "draw_if_possible_failed_ = %d; ", draw_if_possible_failed_);
   base::StringAppendF(&str, "has_pending_tree_ = %d; ", has_pending_tree_);
-  base::StringAppendF(&str, "texture_state_ = %d; ", texture_state_);
-  base::StringAppendF(
-      &str, "output_surface_state_ = %d; ", output_surface_state_);
+  base::StringAppendF(&str,
+      "pending_tree_is_ready_for_activation_ = %d; ",
+      pending_tree_is_ready_for_activation_);
+  base::StringAppendF(&str, "active_tree_has_been_drawn_ = %d; ",
+                      active_tree_has_been_drawn_);
+  base::StringAppendF(&str, "active_tree_is_null_ = %d; ",
+                      active_tree_is_null_);
   return str;
 }
 
 bool SchedulerStateMachine::HasDrawnThisFrame() const {
-  return current_frame_number_ == last_frame_number_where_draw_was_called_;
+  return begin_frame_count_ == last_begin_frame_count_draw_was_called_;
 }
 
-bool SchedulerStateMachine::HasAttemptedTreeActivationThisFrame() const {
-  return current_frame_number_ ==
-         last_frame_number_where_tree_activation_attempted_;
+bool SchedulerStateMachine::HasDrawnThisDrawAttempt() const {
+  return draw_attempt_count_ == last_draw_attempt_count_draw_was_called_;
 }
 
-bool SchedulerStateMachine::HasUpdatedVisibleTilesThisFrame() const {
-  return current_frame_number_ ==
-         last_frame_number_where_update_visible_tiles_was_called_;
+bool SchedulerStateMachine::HasSentBeginFrameToMainThreadThisFrame() const {
+  return begin_frame_count_ ==
+         last_begin_frame_count_begin_frame_sent_to_main_thread_;
 }
 
-void SchedulerStateMachine::SetPostCommitFlags() {
-  // This post-commit work is common to both completed and aborted commits.
-  if (needs_forced_redraw_after_next_commit_) {
-    needs_forced_redraw_after_next_commit_ = false;
-    needs_forced_redraw_ = true;
-  }
-  if (needs_redraw_after_next_commit_) {
-    needs_redraw_after_next_commit_ = false;
-    needs_redraw_ = true;
+bool SchedulerStateMachine::HasUpdatedVisibleTilesThisDrawAttempt() const {
+  return draw_attempt_count_ ==
+         last_draw_attempt_count_update_visible_tiles_was_called_;
+}
+
+bool SchedulerStateMachine::HasActivatedPendingTreeThisDrawAttempt() const {
+  return draw_attempt_count_ ==
+         last_draw_attempt_count_tree_activation_attempted_;
+}
+
+void SchedulerStateMachine::HandleCommitInternal(bool commit_was_aborted) {
+  commit_count_++;
+  draw_attempt_count_++;
+
+  // If we are impl-side-painting but the commit was aborted, then we behave
+  // as if we are not impl-side-painting since there is no pending tree.
+  if (settings_.impl_side_painting && !commit_was_aborted) {
+    commit_state_ = COMMIT_STATE_WAITING_FOR_ACTIVATION;
+
+    if (output_surface_state_ == OUTPUT_SURFACE_WAITING_FOR_FIRST_COMMIT)
+      output_surface_state_ = OUTPUT_SURFACE_WAITING_FOR_FIRST_ACTIVATION;
+
+    if (forced_redraw_state_ == FORCED_REDRAW_STATE_WAITING_FOR_COMMIT)
+      forced_redraw_state_ = FORCED_REDRAW_STATE_WAITING_FOR_ACTIVATION;
+    else if (readback_state_ == READBACK_STATE_FORCED_COMMIT_PENDING)
+      readback_state_ = READBACK_STATE_WAITING_FOR_ACTIVATION;
+    else if (readback_state_ == READBACK_STATE_REPLACEMENT_COMMIT_PENDING)
+      readback_state_ = READBACK_STATE_REPLACEMENT_COMMIT_ACTIVATING;
+
+  } else {
+    if (output_surface_state_ == OUTPUT_SURFACE_WAITING_FOR_FIRST_COMMIT) {
+      output_surface_state_ = OUTPUT_SURFACE_ACTIVE;
+      needs_redraw_ = true;
+    }
+
+    if (forced_redraw_state_ == FORCED_REDRAW_STATE_WAITING_FOR_COMMIT)
+      forced_redraw_state_ = FORCED_REDRAW_STATE_WAITING_FOR_DRAW;
+    else if (readback_state_ == READBACK_STATE_FORCED_COMMIT_PENDING)
+      readback_state_ = READBACK_STATE_WAITING_FOR_DRAW_AND_READBACK;
+    else if (readback_state_ == READBACK_STATE_REPLACEMENT_COMMIT_PENDING)
+      readback_state_ = READBACK_STATE_IDLE;
+
+    if (draw_if_possible_failed_) {
+      last_begin_frame_count_draw_was_called_ = -1;
+      last_draw_attempt_count_draw_was_called_ = -1;
+    }
+
+    if (commit_was_aborted) {
+      if (forced_redraw_state_ == FORCED_REDRAW_STATE_WAITING_FOR_DRAW ||
+          readback_state_ == READBACK_STATE_FORCED_COMMIT_PENDING)
+        commit_state_ = COMMIT_STATE_WAITING_FOR_FIRST_DRAW;
+      else
+        commit_state_ = COMMIT_STATE_IDLE;
+    } else {
+      commit_state_ = COMMIT_STATE_WAITING_FOR_FIRST_DRAW;
+      active_tree_has_been_drawn_ = false;
+      needs_redraw_ = true;
+    }
   }
+
   texture_state_ = LAYER_TEXTURE_STATE_ACQUIRED_BY_IMPL_THREAD;
 }
 
@@ -150,12 +201,43 @@ bool SchedulerStateMachine::ScheduledToDraw() const {
 }
 
 bool SchedulerStateMachine::ShouldDraw() const {
-  if (needs_forced_redraw_)
+  if (HasDrawnThisDrawAttempt())
+    return false;
+
+  // After a readback, make sure not to draw again until we've replaced the
+  // readback commit with a real one.
+  if (readback_state_ == READBACK_STATE_REPLACEMENT_COMMIT_PENDING ||
+      readback_state_ == READBACK_STATE_REPLACEMENT_COMMIT_ACTIVATING)
+    return false;
+
+  // Draw outside of the BeginFrame deadline for readbacks.
+  if (readback_state_ == READBACK_STATE_WAITING_FOR_DRAW_AND_READBACK) {
+    DCHECK_EQ(commit_state_, COMMIT_STATE_WAITING_FOR_FIRST_DRAW);
     return true;
+  }
 
-  if (!ScheduledToDraw())
+  // If we've lost the output surface or draw is suspended, we want to be able
+  // to abort a draw and make forward progress to unblock the main thread.
+  if (output_surface_state_ != OUTPUT_SURFACE_ACTIVE ||
+      DrawSuspendedUntilCommit()) {
+    return !active_tree_has_been_drawn_ &&
+           (commit_state_ == COMMIT_STATE_WAITING_FOR_FIRST_DRAW ||
+            commit_state_ == COMMIT_STATE_WAITING_FOR_ACTIVATION ||
+            (output_surface_state_ != OUTPUT_SURFACE_ACTIVE &&
+             !active_tree_is_null_));
+  }
+
+  // Except for the cases above, do not draw outside of the BeginFrame deadline.
+  if (begin_frame_state_ != BEGIN_FRAME_STATE_INSIDE_DEADLINE)
     return false;
-  if (!inside_begin_frame_)
+
+  // Only handle forced redraws due to timeouts on the regular deadline.
+  if (forced_redraw_state_ == FORCED_REDRAW_STATE_WAITING_FOR_DRAW) {
+    DCHECK_EQ(commit_state_, COMMIT_STATE_WAITING_FOR_FIRST_DRAW);
+    return true;
+  }
+
+  if (!ScheduledToDraw())
     return false;
   if (HasDrawnThisFrame())
     return false;
@@ -164,18 +246,45 @@ bool SchedulerStateMachine::ShouldDraw() const {
   return true;
 }
 
-bool SchedulerStateMachine::ShouldAttemptTreeActivation() const {
-  return has_pending_tree_ && inside_begin_frame_ &&
-         !HasAttemptedTreeActivationThisFrame();
+bool SchedulerStateMachine::ShouldActivatePendingTree() const {
+  // Some quick early outs.
+  if (!has_pending_tree_)
+    return false;
+  if (HasActivatedPendingTreeThisDrawAttempt())
+    return false;
+
+  // If this is our first activation, we don't want to activate early.
+  if (output_surface_state_ == OUTPUT_SURFACE_WAITING_FOR_FIRST_ACTIVATION)
+    return pending_tree_is_ready_for_activation_;
+
+  // In these cases, we want to activate even if the pending tree isn't ready

[enne (OOO), 2013/08/02 19:41:25]

This looks really good.  This is what I was trying to get at with the TODO(enne)
in this file and am kind of surprised it hasn't bitten us sooner.

+  // because we aren't going to draw the pending tree or need to make
+  // forward progress to unblock the main thread.
+  if (!visible_ ||
+      output_surface_state_ == OUTPUT_SURFACE_LOST ||
+      output_surface_state_ == OUTPUT_SURFACE_CREATING ||
+      output_surface_state_ == OUTPUT_SURFACE_WAITING_FOR_FIRST_COMMIT)
+    return true;
+
+  // After this line, we only want to activate if we are ready to activate.
+  if (!pending_tree_is_ready_for_activation_)
+    return false;
+

[enne (OOO), 2013/08/02 19:41:25]

This comment doesn't really add much, and I don't understand why you wouldn't
want to activate here.  Can you explain this more?

[brianderson, 2013/08/02 23:04:31]

Good catch! This needlessly delays activation. I probably would have caught this
myself if I tried writing a better comment in the first place. =)

+  // Do not activate in BEGIN_FRAME_STATE_IDLE
+  if (begin_frame_state_ == BEGIN_FRAME_STATE_IDLE)
+    return false;
+
+  // We do not want to activate a second tree before drawing the first one.

[enne (OOO), 2013/08/02 19:41:25]

How is that possible? Maybe I'm misreading other parts of this patch, but
previous we wouldn't send a new begin frame message to the main thread to start
a commit until we'd drawn from the previous commit.  And you can't activate
until you've started another commit.

It seems like that's still the case given that you check for COMMIT_STATE_IDLE
in SchedulerStateMachine::ShouldSendBeginFrameToMainThread().  Am I missing
something?

[brianderson, 2013/08/02 23:04:31]

In this patch, the draw no longer has to occur before we send the begin frame to
the main thread.  When impl-side-painting, there is a new
COMMIT_STATE_WAITING_FOR_ACTIVATION that transitions to COMMIT_STATE_IDLE on
activation rather than to COMMIT_STATE_WAITING_FOR_FIRST_DRAW. So it is now
possible for us to start (and finish) another commit before we've drawn the
previous one.

+  return active_tree_has_been_drawn_ || active_tree_is_null_;

[enne (OOO), 2013/08/02 19:41:25]

There are other reasons that the active tree might not have drawn (e.g.
everything in CanDraw).  It seems like maybe active_tree_is_null_ in this check
should be replaced by !can_draw_?

[brianderson, 2013/08/02 23:04:31]

In cases where can_draw_ is false, ACTION_DRAW_AND_SWAP_ABORT will set
active_tree_has_been_drawn_ to true, which will in turn unblock activation. I
will add a comment to explain.

At one point I was using can_draw_ to unblock activation, but that resulted in
checkerboarding when switching to a new tab.

[enne (OOO), 2013/08/05 19:37:43]

In that case, shouldn't that logic to set active_tree_has_been_drawn to true
when it can't be drawn mean that you don't need the active_tree_is_null clause
here?

[brianderson, 2013/08/05 21:56:19]

As it is currently coded, ShouldDraw() will not return true when
active_tree_is_null_, which is why the active_tree_is_null_ clause is needed
here.

I just tried removing the checks for active_tree_is_null_ in ShouldDraw() and
ShouldActivatePendingTree(). It appears to work and results in less code.
Conceptually though, it seems strange to try to draw when there is no active
tree. The intention of the ACTION_DRAW_AND_SWAP_ABORT was to unblock a draw that
was initiated but could never happen.

 }
 
 bool SchedulerStateMachine::ShouldUpdateVisibleTiles() const {
   if (!settings_.impl_side_painting)
     return false;
-  if (HasUpdatedVisibleTilesThisFrame())
+  if (HasUpdatedVisibleTilesThisDrawAttempt())
     return false;
 
-  return ShouldAttemptTreeActivation() || ShouldDraw() ||
+  return ShouldActivatePendingTree() || ShouldDraw() ||
          swap_used_incomplete_tile_;
 }
 
@@ -194,89 +303,136 @@ bool SchedulerStateMachine::ShouldAcquireLayerTexturesForMainThread() const {
   return false;
 }
 
+bool SchedulerStateMachine::ShouldSendBeginFrameToMainThread() const {
+  if (HasSentBeginFrameToMainThreadThisFrame())
+    return false;
+
+  // Only send BeginFrame to the main thread when idle.
+  if (commit_state_ != COMMIT_STATE_IDLE)
+    return false;
+
+  // We can't accept a commit if we have a pending tree.
+  if (has_pending_tree_)
+    return false;
+
+  // We want to handle readback commits ASAP.
+  if (readback_state_ == READBACK_STATE_FORCED_COMMIT_REQUESTED)
+    return !CommitPending();
+
+  // We want to start the first commit after we get a new output surface
+  // immediately.
+  if (output_surface_state_ == OUTPUT_SURFACE_WAITING_FOR_FIRST_COMMIT
+      && needs_commit_)
+    return true;
+
+  // We usually want to slave the main thread's BeginFrame to the impl thread's
+  // BeginFrame. However, if we aren't expecting a BeginFrame on the impl
+  // thread, we should send a BeginFrame to the main thread anyway to make
+  // progress.
+  // TODO(brianderson): Also allow sending BeginFrame to main thread while idle
+  // when the main thread isn't consuming user input.
+  if (begin_frame_state_ == BEGIN_FRAME_STATE_IDLE &&
+      BeginFrameNeededByImplThread())
+    return false;
+
+  // Do not send begin frame to main thread in the deadline until we have drawn.
+  // We have a train to catch!
+  if (begin_frame_state_ == BEGIN_FRAME_STATE_INSIDE_DEADLINE &&
+      !HasDrawnThisFrame())
+    return false;
+
+  // If not impl-side-painting, do not send a BeginFrame to the main thread if
+  // we haven't drawn the active tree. Otherwise, the commit overwrite the
+  // active tree before we have a chance to draw it.
+  if (!settings_.impl_side_painting &&
+      !active_tree_has_been_drawn_ &&
+      !active_tree_is_null_)
+    return false;
+
+  bool can_commit = needs_commit_ &&
+      (visible_ ||
+       forced_redraw_state_ == FORCED_REDRAW_STATE_WAITING_FOR_COMMIT);
+  return can_commit &&
+          (forced_redraw_state_ == FORCED_REDRAW_STATE_WAITING_FOR_COMMIT ||
+           HasInitializedOutputSurface());
+}
+
 SchedulerStateMachine::Action SchedulerStateMachine::NextAction() const {
   if (ShouldAcquireLayerTexturesForMainThread())
     return ACTION_ACQUIRE_LAYER_TEXTURES_FOR_MAIN_THREAD;
 
   switch (commit_state_) {
-    case COMMIT_STATE_IDLE: {
-      if (output_surface_state_ != OUTPUT_SURFACE_ACTIVE &&
-          needs_forced_redraw_)
-        return ACTION_DRAW_FORCED;
-      if (output_surface_state_ != OUTPUT_SURFACE_ACTIVE &&
-          needs_forced_commit_)
-        // TODO(enne): Should probably drop the active tree on force commit.
-        return has_pending_tree_ ? ACTION_NONE
-                                 : ACTION_SEND_BEGIN_FRAME_TO_MAIN_THREAD;
+    case COMMIT_STATE_IDLE:
+      if (ShouldSendBeginFrameToMainThread())
+        return ACTION_SEND_BEGIN_FRAME_TO_MAIN_THREAD;
       if (output_surface_state_ == OUTPUT_SURFACE_LOST && can_start_)
         return ACTION_BEGIN_OUTPUT_SURFACE_CREATION;
       if (output_surface_state_ == OUTPUT_SURFACE_CREATING)
         return ACTION_NONE;
       if (ShouldUpdateVisibleTiles())
         return ACTION_UPDATE_VISIBLE_TILES;
-      if (ShouldAttemptTreeActivation())
-        return ACTION_ACTIVATE_PENDING_TREE_IF_NEEDED;
+      if (ShouldActivatePendingTree())
+        return ACTION_ACTIVATE_PENDING_TREE;
       if (ShouldDraw()) {
-        return needs_forced_redraw_ ? ACTION_DRAW_FORCED
-                                    : ACTION_DRAW_IF_POSSIBLE;
+        if (output_surface_state_ != OUTPUT_SURFACE_ACTIVE ||
+            DrawSuspendedUntilCommit())
+          return ACTION_DRAW_AND_SWAP_ABORT;
+        else
+          return ACTION_DRAW_AND_SWAP_IF_POSSIBLE;
       }
-      bool can_commit_this_frame =
-          visible_ &&
-          current_frame_number_ >
-              last_frame_number_where_begin_frame_sent_to_main_thread_;
-      if (needs_commit_ && ((can_commit_this_frame &&
-                             output_surface_state_ == OUTPUT_SURFACE_ACTIVE) ||
-                            needs_forced_commit_))
-        // TODO(enne): Should probably drop the active tree on force commit.
-        return has_pending_tree_ ? ACTION_NONE
-                                 : ACTION_SEND_BEGIN_FRAME_TO_MAIN_THREAD;
       return ACTION_NONE;
-    }
+
     case COMMIT_STATE_FRAME_IN_PROGRESS:
       if (ShouldUpdateVisibleTiles())
         return ACTION_UPDATE_VISIBLE_TILES;
-      if (ShouldAttemptTreeActivation())
-        return ACTION_ACTIVATE_PENDING_TREE_IF_NEEDED;
+      if (ShouldActivatePendingTree())
+        return ACTION_ACTIVATE_PENDING_TREE;
       if (ShouldDraw()) {
-        return needs_forced_redraw_ ? ACTION_DRAW_FORCED
-                                    : ACTION_DRAW_IF_POSSIBLE;
+        if (output_surface_state_ != OUTPUT_SURFACE_ACTIVE ||
+            DrawSuspendedUntilCommit())
+          return ACTION_DRAW_AND_SWAP_ABORT;
+        else
+          return ACTION_DRAW_AND_SWAP_IF_POSSIBLE;
       }
       return ACTION_NONE;
 
     case COMMIT_STATE_READY_TO_COMMIT:
       return ACTION_COMMIT;
 
-    case COMMIT_STATE_WAITING_FOR_FIRST_DRAW: {
+    case COMMIT_STATE_WAITING_FOR_ACTIVATION: {
       if (ShouldUpdateVisibleTiles())
         return ACTION_UPDATE_VISIBLE_TILES;
-      if (ShouldAttemptTreeActivation())
-        return ACTION_ACTIVATE_PENDING_TREE_IF_NEEDED;
-      if (ShouldDraw() || output_surface_state_ == OUTPUT_SURFACE_LOST) {
-        return needs_forced_redraw_ ? ACTION_DRAW_FORCED
-                                    : ACTION_DRAW_IF_POSSIBLE;
+      if (ShouldActivatePendingTree())
+        return ACTION_ACTIVATE_PENDING_TREE;
+      if (ShouldDraw()) {
+        if (output_surface_state_ != OUTPUT_SURFACE_ACTIVE ||
+            DrawSuspendedUntilCommit())
+          return ACTION_DRAW_AND_SWAP_ABORT;
+        else
+          return ACTION_DRAW_AND_SWAP_IF_POSSIBLE;
       }
-      // COMMIT_STATE_WAITING_FOR_FIRST_DRAW wants to enforce a draw. If
-      // can_draw_ is false or textures are not available, proceed to the next
-      // step (similar as in COMMIT_STATE_IDLE).
-      bool can_commit =
-          needs_forced_commit_ ||
-          (visible_ &&
-           current_frame_number_ >
-               last_frame_number_where_begin_frame_sent_to_main_thread_);
-      if (needs_commit_ && can_commit && DrawSuspendedUntilCommit())
-        return has_pending_tree_ ? ACTION_NONE
-                                 : ACTION_SEND_BEGIN_FRAME_TO_MAIN_THREAD;
       return ACTION_NONE;
     }
 
-    case COMMIT_STATE_WAITING_FOR_FIRST_FORCED_DRAW:
+    case COMMIT_STATE_WAITING_FOR_FIRST_DRAW: {
       if (ShouldUpdateVisibleTiles())
         return ACTION_UPDATE_VISIBLE_TILES;
-      if (ShouldAttemptTreeActivation())
-        return ACTION_ACTIVATE_PENDING_TREE_IF_NEEDED;
-      if (needs_forced_redraw_)
-        return ACTION_DRAW_FORCED;
+      if (ShouldActivatePendingTree())
+        return ACTION_ACTIVATE_PENDING_TREE;
+      if (ShouldDraw()) {
+        if (forced_redraw_state_ == FORCED_REDRAW_STATE_WAITING_FOR_DRAW)
+          return ACTION_DRAW_AND_SWAP_FORCED;
+        else if (readback_state_ ==
+                 READBACK_STATE_WAITING_FOR_DRAW_AND_READBACK)
+          return ACTION_DRAW_AND_READBACK;
+        else if (output_surface_state_ != OUTPUT_SURFACE_ACTIVE ||
+                 DrawSuspendedUntilCommit())
+          return ACTION_DRAW_AND_SWAP_ABORT;
+        else
+          return ACTION_DRAW_AND_SWAP_IF_POSSIBLE;
+      }
       return ACTION_NONE;
+    }
   }
   NOTREACHED();
   return ACTION_NONE;
@@ -288,60 +444,56 @@ void SchedulerStateMachine::UpdateState(Action action) {
       return;
 
     case ACTION_UPDATE_VISIBLE_TILES:
-      last_frame_number_where_update_visible_tiles_was_called_ =
-          current_frame_number_;
+      last_draw_attempt_count_update_visible_tiles_was_called_ =
+          draw_attempt_count_;
       return;
 
-    case ACTION_ACTIVATE_PENDING_TREE_IF_NEEDED:
-      last_frame_number_where_tree_activation_attempted_ =
-          current_frame_number_;
+    case ACTION_ACTIVATE_PENDING_TREE:
+      last_draw_attempt_count_tree_activation_attempted_ =
+          draw_attempt_count_;
       return;
 
     case ACTION_SEND_BEGIN_FRAME_TO_MAIN_THREAD:
       DCHECK(!has_pending_tree_);
-      if (!needs_forced_commit_) {
-        DCHECK(visible_);
-        DCHECK_GT(current_frame_number_,
-                  last_frame_number_where_begin_frame_sent_to_main_thread_);
-      }
+      DCHECK(visible_ ||
+             readback_state_ == READBACK_STATE_FORCED_COMMIT_REQUESTED ||
+             forced_redraw_state_ == FORCED_REDRAW_STATE_WAITING_FOR_COMMIT ||
+             output_surface_state_ == OUTPUT_SURFACE_WAITING_FOR_FIRST_COMMIT);
       commit_state_ = COMMIT_STATE_FRAME_IN_PROGRESS;
       needs_commit_ = false;
-      needs_forced_commit_ = false;
-      last_frame_number_where_begin_frame_sent_to_main_thread_ =
-          current_frame_number_;
+      if (readback_state_ == READBACK_STATE_FORCED_COMMIT_REQUESTED)
+        readback_state_ = READBACK_STATE_FORCED_COMMIT_PENDING;
+      last_begin_frame_count_begin_frame_sent_to_main_thread_ =
+          begin_frame_count_;
       return;
 
     case ACTION_COMMIT:
-      commit_count_++;
-      if (expect_immediate_begin_frame_for_main_thread_)
-        commit_state_ = COMMIT_STATE_WAITING_FOR_FIRST_FORCED_DRAW;
-      else
-        commit_state_ = COMMIT_STATE_WAITING_FOR_FIRST_DRAW;
-      // When impl-side painting, we draw on activation instead of on commit.
-      if (!settings_.impl_side_painting)
-        needs_redraw_ = true;
-      if (draw_if_possible_failed_)
-        last_frame_number_where_draw_was_called_ = -1;
-      SetPostCommitFlags();
+      HandleCommitInternal(false);
       return;
 
-    case ACTION_DRAW_FORCED:
-    case ACTION_DRAW_IF_POSSIBLE:
-      needs_redraw_ = false;
-      needs_forced_redraw_ = false;
-      draw_if_possible_failed_ = false;
-      swap_used_incomplete_tile_ = false;
-      if (inside_begin_frame_)
-        last_frame_number_where_draw_was_called_ = current_frame_number_;
-      if (commit_state_ == COMMIT_STATE_WAITING_FOR_FIRST_FORCED_DRAW) {
-        DCHECK(expect_immediate_begin_frame_for_main_thread_);
+    case ACTION_DRAW_AND_SWAP_IF_POSSIBLE:
+    case ACTION_DRAW_AND_SWAP_FORCED:
+    case ACTION_DRAW_AND_READBACK:
+    case ACTION_DRAW_AND_SWAP_ABORT:
+      if (forced_redraw_state_ == FORCED_REDRAW_STATE_WAITING_FOR_DRAW) {
+        commit_state_ = COMMIT_STATE_IDLE;
+        forced_redraw_state_ = FORCED_REDRAW_STATE_IDLE;
+      } else if (readback_state_ ==
+                 READBACK_STATE_WAITING_FOR_DRAW_AND_READBACK) {
+        DCHECK(!has_pending_tree_);
         commit_state_ = COMMIT_STATE_FRAME_IN_PROGRESS;
-        expect_immediate_begin_frame_for_main_thread_ = false;
+        readback_state_ = READBACK_STATE_REPLACEMENT_COMMIT_PENDING;
       } else if (commit_state_ == COMMIT_STATE_WAITING_FOR_FIRST_DRAW) {
         commit_state_ = COMMIT_STATE_IDLE;
       }
+      needs_redraw_ = false;
+      draw_if_possible_failed_ = false;
+      swap_used_incomplete_tile_ = false;
+      last_begin_frame_count_draw_was_called_ = begin_frame_count_;
+      last_draw_attempt_count_draw_was_called_ = draw_attempt_count_;
       if (texture_state_ == LAYER_TEXTURE_STATE_ACQUIRED_BY_IMPL_THREAD)
         texture_state_ = LAYER_TEXTURE_STATE_UNLOCKED;
+      active_tree_has_been_drawn_ = true;
       return;
 
     case ACTION_BEGIN_OUTPUT_SURFACE_CREATION:
@@ -357,49 +509,88 @@ void SchedulerStateMachine::UpdateState(Action action) {
   }
 }
 
+void SchedulerStateMachine::AdvanceBeginFrameStateWhenNoActionsRemain() {
+  switch (begin_frame_state_) {
+    case BEGIN_FRAME_STATE_INSIDE_BEGIN_FRAME:
+        begin_frame_state_ = BEGIN_FRAME_STATE_DEADLINE_PENDING;
+        break;
+    case BEGIN_FRAME_STATE_INSIDE_DEADLINE:
+        begin_frame_state_ = BEGIN_FRAME_STATE_IDLE;
+        break;
+    case BEGIN_FRAME_STATE_IDLE:
+    case BEGIN_FRAME_STATE_DEADLINE_PENDING:
+        break;
+  }
+}
+
 void SchedulerStateMachine::SetMainThreadNeedsLayerTextures() {
   DCHECK(!main_thread_needs_layer_textures_);
   DCHECK_NE(texture_state_, LAYER_TEXTURE_STATE_ACQUIRED_BY_MAIN_THREAD);
   main_thread_needs_layer_textures_ = true;
 }
 
+bool SchedulerStateMachine::BeginFrameNeededByImplThread() const {
+  return BeginFrameNeededToDrawByImplThread() ||
+         BeginFrameProactivelyNeededByImplThread();
+}
+
 bool SchedulerStateMachine::BeginFrameNeededToDrawByImplThread() const {
   // If we can't draw, don't tick until we are notified that we can draw again.
   if (!can_draw_)
     return false;
 
-  if (needs_forced_redraw_)
+  if (forced_redraw_state_ == FORCED_REDRAW_STATE_WAITING_FOR_DRAW)
     return true;
 
   if (visible_ && swap_used_incomplete_tile_)
     return true;
 
-  return needs_redraw_ && visible_ &&
-         output_surface_state_ == OUTPUT_SURFACE_ACTIVE;
+  return needs_redraw_ && visible_ && HasInitializedOutputSurface();
 }
 
-bool SchedulerStateMachine::ProactiveBeginFrameWantedByImplThread() const {
-  // Do not be proactive when invisible.
-  if (!visible_ || output_surface_state_ != OUTPUT_SURFACE_ACTIVE)
+bool SchedulerStateMachine::BeginFrameProactivelyNeededByImplThread() const {
+  if (settings_.using_synchronous_renderer_compositor)
+    return false;
+
+  if (!settings_.throttle_frame_production)
+    return false;
+
+  if (!visible_ || !HasInitializedOutputSurface())
     return false;
 
   // We should proactively request a BeginFrame if a commit or a tree activation
   // is pending.
-  return (needs_commit_ || needs_forced_commit_ ||
-          commit_state_ != COMMIT_STATE_IDLE || has_pending_tree_);
+  return (needs_commit_ ||
+          commit_state_ != COMMIT_STATE_IDLE ||
+          has_pending_tree_);
 }
 
-void SchedulerStateMachine::DidEnterBeginFrame(const BeginFrameArgs& args) {
-  current_frame_number_++;
-  inside_begin_frame_ = true;
+void SchedulerStateMachine::OnBeginFrame(const BeginFrameArgs& args) {
+  begin_frame_count_++;
+  draw_attempt_count_++;
   last_begin_frame_args_ = args;
+  begin_frame_state_ = BEGIN_FRAME_STATE_INSIDE_BEGIN_FRAME;
+}
+
+bool SchedulerStateMachine::ShouldTriggerBeginFrameDeadlineEarly() const {
+  // TODO(brianderson): This should take into account multiple commit sources.
+  return begin_frame_state_ == BEGIN_FRAME_STATE_DEADLINE_PENDING &&
+         !active_tree_has_been_drawn_;
+}
+
+bool SchedulerStateMachine::InsideBeginFrame() const {
+  return begin_frame_state_ != BEGIN_FRAME_STATE_IDLE;
 }
 
-void SchedulerStateMachine::DidLeaveBeginFrame() {
-  inside_begin_frame_ = false;
+void SchedulerStateMachine::OnBeginFrameDeadline() {
+  DCHECK_EQ(begin_frame_state_, BEGIN_FRAME_STATE_DEADLINE_PENDING);
+  draw_attempt_count_++;
+  begin_frame_state_ = BEGIN_FRAME_STATE_INSIDE_DEADLINE;
 }
 
-void SchedulerStateMachine::SetVisible(bool visible) { visible_ = visible; }
+void SchedulerStateMachine::SetVisible(bool visible) {
+  visible_ = visible;
+}
 
 void SchedulerStateMachine::SetNeedsRedraw() { needs_redraw_ = true; }
 
@@ -407,10 +598,6 @@ void SchedulerStateMachine::DidSwapUseIncompleteTile() {
   swap_used_incomplete_tile_ = true;
 }
 
-void SchedulerStateMachine::SetNeedsForcedRedraw() {
-  needs_forced_redraw_ = true;
-}
-
 void SchedulerStateMachine::DidDrawIfPossibleCompleted(bool success) {
   draw_if_possible_failed_ = !success;
   if (draw_if_possible_failed_) {
@@ -423,7 +610,7 @@ void SchedulerStateMachine::DidDrawIfPossibleCompleted(bool success) {
       consecutive_failed_draws_ = 0;
       // We need to force a draw, but it doesn't make sense to do this until
       // we've committed and have new textures.
-      needs_forced_redraw_after_next_commit_ = true;
+      forced_redraw_state_ = FORCED_REDRAW_STATE_WAITING_FOR_COMMIT;
     }
   } else {
     consecutive_failed_draws_ = 0;
@@ -432,26 +619,27 @@ void SchedulerStateMachine::DidDrawIfPossibleCompleted(bool success) {
 
 void SchedulerStateMachine::SetNeedsCommit() { needs_commit_ = true; }
 
-void SchedulerStateMachine::SetNeedsForcedCommit() {
-  needs_forced_commit_ = true;
-  expect_immediate_begin_frame_for_main_thread_ = true;
+void SchedulerStateMachine::SetNeedsForcedCommitForReadback() {
+  DCHECK_EQ(readback_state_, READBACK_STATE_IDLE);
+  if (commit_state_ == COMMIT_STATE_FRAME_IN_PROGRESS)
+    readback_state_ = READBACK_STATE_FORCED_COMMIT_PENDING;
+  else
+    readback_state_ = READBACK_STATE_FORCED_COMMIT_REQUESTED;
 }
 
 void SchedulerStateMachine::FinishCommit() {
   DCHECK(commit_state_ == COMMIT_STATE_FRAME_IN_PROGRESS ||
-         (expect_immediate_begin_frame_for_main_thread_ &&
-          commit_state_ != COMMIT_STATE_IDLE))
+         readback_state_ == READBACK_STATE_FORCED_COMMIT_PENDING)
       << ToString();
   commit_state_ = COMMIT_STATE_READY_TO_COMMIT;
 }
 
 void SchedulerStateMachine::BeginFrameAbortedByMainThread(bool did_handle) {
   DCHECK_EQ(commit_state_, COMMIT_STATE_FRAME_IN_PROGRESS);
-  if (expect_immediate_begin_frame_for_main_thread_) {
-    expect_immediate_begin_frame_for_main_thread_ = false;
+  if (readback_state_ == READBACK_STATE_FORCED_COMMIT_REQUESTED) {
+    readback_state_ = READBACK_STATE_IDLE;
   } else if (did_handle) {
-    commit_state_ = COMMIT_STATE_IDLE;
-    SetPostCommitFlags();
+    HandleCommitInternal(true);
   } else {
     commit_state_ = COMMIT_STATE_IDLE;
     SetNeedsCommit();
@@ -463,33 +651,67 @@ void SchedulerStateMachine::DidLoseOutputSurface() {
       output_surface_state_ == OUTPUT_SURFACE_CREATING)
     return;
   output_surface_state_ = OUTPUT_SURFACE_LOST;
+  needs_redraw_ = false;
+}
+
+void SchedulerStateMachine::NotifyReadyToActivate() {
+  if (has_pending_tree_)
+    pending_tree_is_ready_for_activation_ = true;
 }
 
-void SchedulerStateMachine::SetHasPendingTree(bool has_pending_tree) {
+void SchedulerStateMachine::SetHasTrees(bool has_pending_tree,
+                                        bool active_tree_is_null) {
+  active_tree_is_null_ = active_tree_is_null;
+  if (has_pending_tree_ && !has_pending_tree) {
+    // There is a new active tree.
+    draw_attempt_count_++;
+    pending_tree_is_ready_for_activation_ = false;
+    active_tree_has_been_drawn_ = false;
+    needs_redraw_ = true;
+
+    if (draw_if_possible_failed_) {
+      last_begin_frame_count_draw_was_called_ = -1;
+      last_draw_attempt_count_draw_was_called_ = -1;
+    }
+
+    if (output_surface_state_ == OUTPUT_SURFACE_WAITING_FOR_FIRST_ACTIVATION)
+      output_surface_state_ = OUTPUT_SURFACE_ACTIVE;
+
+    DCHECK_EQ(COMMIT_STATE_WAITING_FOR_ACTIVATION, commit_state_);
+    if (forced_redraw_state_ == FORCED_REDRAW_STATE_WAITING_FOR_ACTIVATION) {
+      commit_state_ = COMMIT_STATE_WAITING_FOR_FIRST_DRAW;
+      forced_redraw_state_ = FORCED_REDRAW_STATE_WAITING_FOR_DRAW;
+    } else if (readback_state_ == READBACK_STATE_WAITING_FOR_ACTIVATION) {
+      commit_state_ = COMMIT_STATE_WAITING_FOR_FIRST_DRAW;
+      readback_state_ = READBACK_STATE_WAITING_FOR_DRAW_AND_READBACK;
+    } else {
+      commit_state_ = COMMIT_STATE_IDLE;
+      if (readback_state_ == READBACK_STATE_REPLACEMENT_COMMIT_ACTIVATING)
+        readback_state_ = READBACK_STATE_IDLE;
+    }
+  } else if (!has_pending_tree_ && has_pending_tree) {
+    // There is a new pending tree.
+    pending_tree_is_ready_for_activation_ = false;
+  }
+
   has_pending_tree_ = has_pending_tree;
 }
 
-void SchedulerStateMachine::SetCanDraw(bool can) { can_draw_ = can; }
+void SchedulerStateMachine::SetCanDraw(bool can_draw) {
+  can_draw_ = can_draw;
+}
 
 void SchedulerStateMachine::DidCreateAndInitializeOutputSurface() {
   DCHECK_EQ(output_surface_state_, OUTPUT_SURFACE_CREATING);
-  output_surface_state_ = OUTPUT_SURFACE_ACTIVE;
-
-  if (did_create_and_initialize_first_output_surface_) {
-    // TODO(boliu): See if we can remove this when impl-side painting is always
-    // on. Does anything on the main thread need to update after recreate?
+  output_surface_state_ = OUTPUT_SURFACE_WAITING_FOR_FIRST_COMMIT;
+  if (did_create_and_initialize_first_output_surface_)
     needs_commit_ = true;
-    // If anything has requested a redraw, we don't want to actually draw
-    // when the output surface is restored until things have a chance to
-    // sort themselves out with a commit.
-    needs_redraw_ = false;
-  }
-  needs_redraw_after_next_commit_ = true;
   did_create_and_initialize_first_output_surface_ = true;
 }
 
 bool SchedulerStateMachine::HasInitializedOutputSurface() const {
-  return output_surface_state_ == OUTPUT_SURFACE_ACTIVE;
+  return output_surface_state_ != OUTPUT_SURFACE_LOST &&
+         output_surface_state_ != OUTPUT_SURFACE_CREATING;
 }
 
 void SchedulerStateMachine::SetMaximumNumberOfFailedDrawsBeforeDrawIsForced(