cc: Simplify the logic for deciding to update tile priorities.

cc/layer_tree_impl.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/layer_tree_impl.h"
 
 #include "base/debug/trace_event.h"
 #include "cc/heads_up_display_layer_impl.h"
 #include "cc/layer_tree_host_common.h"
 #include "cc/layer_tree_host_impl.h"
@@ skipping 11 matching lines @@
       has_transparent_background_(false),
       page_scale_factor_(1),
       page_scale_delta_(1),
       sent_page_scale_delta_(1),
       min_page_scale_factor_(0),
       max_page_scale_factor_(0),
       scrolling_layer_id_from_previous_tree_(0),
       contents_textures_purged_(false),
       viewport_size_invalid_(false),
       needs_update_draw_properties_(true),
+      needs_update_tile_priorities_(false),
       needs_full_tree_sync_(true) {
 }
 
 LayerTreeImpl::~LayerTreeImpl() {
   // Need to explicitly clear the tree prior to destroying this so that
   // the LayerTreeImpl pointer is still valid in the LayerImpl dtor.
   root_layer_.reset();
 }
 
 static LayerImpl* findRootScrollLayer(LayerImpl* layer)
@@ skipping 170 matching lines @@
 }
 
 struct UpdateTilePrioritiesForLayer {
   void operator()(LayerImpl *layer) {
     layer->updateTilePriorities();
   }
 };
 
 void LayerTreeImpl::UpdateDrawProperties(UpdateDrawPropertiesReason reason) {
   if (!needs_update_draw_properties_) {
-    if (reason == UPDATE_ACTIVE_TREE_FOR_DRAW && RootLayer())
+    if (needs_update_tile_priorities_ && RootLayer()) {
+      DCHECK_EQ(UPDATE_ACTIVE_TREE_FOR_DRAW, reason);

[enne (OOO), 2013/03/04 20:16:39]

The change that added this UpdateDrawProperties reason had good performance
benefits, but I still feel like it's a lot of complexity to keep in your head
about at what point what gets updated and why.

Given that this patch provides needs_update_tile_priorities, can you get rid of
UpdateDrawPropertiesReason using the new flag instead? For instance, it's a
little weird that you have needs_update_tile_priorities, but
update_tile_priorities isn't always equal to it.

       LayerTreeHostCommon::callFunctionForSubtree<UpdateTilePrioritiesForLayer>(
           RootLayer());
+      needs_update_tile_priorities_ = false;
+    }
     return;
   }
 
   needs_update_draw_properties_ = false;
+  needs_update_tile_priorities_ = true;
   render_surface_layer_list_.clear();
 
   // For maxTextureSize.
   if (!layer_tree_host_impl_->renderer())
       return;
 
   if (!RootLayer())
     return;
 
   if (root_scroll_layer_) {
     root_scroll_layer_->setImplTransform(ImplTransform());
     // Setting the impl transform re-sets this.
     needs_update_draw_properties_ = false;
   }
 
   {
     TRACE_EVENT1("cc", "LayerTreeImpl::UpdateDrawProperties", "IsActive", IsActiveTree());
     bool update_tile_priorities =
         reason == UPDATE_PENDING_TREE ||
         reason == UPDATE_ACTIVE_TREE_FOR_DRAW;
     LayerTreeHostCommon::calculateDrawProperties(
         RootLayer(),
         device_viewport_size(),
         device_scale_factor(),
         total_page_scale_factor(),
         MaxTextureSize(),
         settings().canUseLCDText,
         render_surface_layer_list_,
         update_tile_priorities);
+
+    if (update_tile_priorities)
+      needs_update_tile_priorities_ = false;
   }
 
   DCHECK(!needs_update_draw_properties_) <<
       "calcDrawProperties should not set_needs_update_draw_properties()";
 }
 
 static void ClearRenderSurfacesOnLayerImplRecursive(LayerImpl* current)
 {
     DCHECK(current);
     for (size_t i = 0; i < current->children().size(); ++i)
@@ skipping 198 matching lines @@
 
 DebugRectHistory* LayerTreeImpl::debug_rect_history() const {
   return layer_tree_host_impl_->debugRectHistory();
 }
 
 AnimationRegistrar* LayerTreeImpl::animationRegistrar() const {
   return layer_tree_host_impl_->animationRegistrar();
 }
 
 } // namespace cc