cc: Throttle tile priority updates to once a frame.

cc/picture_layer_impl.cc

Index: cc/picture_layer_impl.cc
diff --git a/cc/picture_layer_impl.cc b/cc/picture_layer_impl.cc
index 80bf1fa3ae2e9fef727ef7356e69bace6e4678f5..258c43bbebd206fe02c3d92ad52053e5e8986951 100644
--- a/cc/picture_layer_impl.cc
+++ b/cc/picture_layer_impl.cc
@@ -9,6 +9,7 @@
 #include "cc/checkerboard_draw_quad.h"
 #include "cc/debug_border_draw_quad.h"
 #include "cc/debug_colors.h"
+#include "cc/frame_rate_counter.h"
 #include "cc/layer_tree_impl.h"
 #include "cc/math_util.h"
 #include "cc/quad_sink.h"
@@ -27,6 +28,8 @@ namespace cc {
 PictureLayerImpl::PictureLayerImpl(LayerTreeImpl* treeImpl, int id)
     : LayerImpl(treeImpl, id),
       pile_(PicturePileImpl::Create()),
+      last_source_frame_number_(0),
+      last_impl_frame_number_(0),
       last_update_time_(0),
       last_content_scale_(0),
       ideal_contents_scale_(0),
@@ -66,6 +69,7 @@ void PictureLayerImpl::pushPropertiesTo(LayerImpl* base_layer) {
   layer_impl->SetIsMask(is_mask_);
   layer_impl->TransferTilingSet(tilings_.Pass());
   layer_impl->pile_ = pile_;
+  layer_impl->last_impl_frame_number_ = 0;
   pile_ = PicturePileImpl::Create();
   pile_->set_slow_down_raster_scale_factor(
       layerTreeImpl()->debug_state().slowDownRasterScaleFactor);
@@ -193,7 +197,25 @@ void PictureLayerImpl::dumpLayerProperties(std::string*, int indent) const {
   // TODO(enne): implement me
 }
 
-void PictureLayerImpl::didUpdateTransforms() {
+void PictureLayerImpl::updateTilePriorities() {
+  int current_source_frame_number = layerTreeImpl()->source_frame_number();
+  bool first_update_in_new_source_frame =
+      current_source_frame_number > last_source_frame_number_;

[qinmin, 2013/01/25 05:07:53]

i think it is possible for current_source_frame_number to overflow, so this
statement will not be true when that happens

[danakj, 2013/01/25 05:09:01]

ya you're right, i already switched it to != in the last patch. good catch tho!

+
+  int current_impl_frame_number =
+      layerTreeImpl()->frame_rate_counter()->currentFrameNumber();
+  bool first_frame_in_new_impl_tree =
+      last_impl_frame_number_ == 0 ||
+      current_impl_frame_number == last_impl_frame_number_;
+
+  // In pending tree, this is always called. We update priorities:
+  // - Immediately after a commit (first_update_in_new_source_frame).
+  // - On animation ticks after the first frame in the tree.
+  // In active tree, this is only called during draw. We update priorities:
+  // - On draws after the first frame in the tree.
+  if (first_frame_in_new_impl_tree && !first_update_in_new_source_frame)
+    return;
+
   gfx::Transform current_screen_space_transform =
       screenSpaceTransform();
   double current_time =
@@ -214,6 +236,8 @@ void PictureLayerImpl::didUpdateTransforms() {
       current_screen_space_transform,
       time_delta);
 
+  last_source_frame_number_ = current_source_frame_number;
+  last_impl_frame_number_ = current_impl_frame_number;
   last_screen_space_transform_ = current_screen_space_transform;
   last_update_time_ = current_time;
   last_bounds_ = bounds();