cc: Add support for partial swaps when using impl-side painting.

cc/trees/layer_tree_host_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/trees/layer_tree_host_impl.h"
 
 #include <algorithm>
 #include <limits>
 
 #include "base/basictypes.h"
@@ skipping 1177 matching lines @@
 void LayerTreeHostImpl::DidModifyTilePriorities() {
   DCHECK(settings_.impl_side_painting);
   // Mark priorities as dirty and schedule a ManageTiles().
   tile_priorities_dirty_ = true;
   client_->SetNeedsManageTilesOnImplThread();
 }
 
 void LayerTreeHostImpl::DidInitializeVisibleTile() {
   // TODO(reveman): Determine tiles that changed and only damage
   // what's necessary.
-  SetFullRootLayerDamage();
+  gfx::Rect rect = tile_manager_->GetDamagedRect();
+  if (rect.width() * rect.height() <=
+      DrawViewportSize().width() * DrawViewportSize().height())

[sohanjg, 2014/04/01 12:03:11]

we may optimize this check.

+    SetViewportDamage(rect);
+  else
+    SetFullRootLayerDamage();
+  tile_manager_->ResetDamagedRect();
+
   if (client_ && !client_->IsInsideDraw())
     client_->DidInitializeVisibleTileOnImplThread();
 }
 
 void LayerTreeHostImpl::NotifyReadyToActivate() {
   client_->NotifyReadyToActivate();
 }
 
 void LayerTreeHostImpl::SetMemoryPolicy(const ManagedMemoryPolicy& policy) {
   SetManagedMemoryPolicy(policy, zero_budget_);
@@ skipping 376 matching lines @@
   CHECK(!pending_tree_);
   if (recycle_tree_)
     recycle_tree_.swap(pending_tree_);
   else
     pending_tree_ = LayerTreeImpl::create(this);
   client_->OnCanDrawStateChanged(CanDraw());
   TRACE_EVENT_ASYNC_BEGIN0("cc", "PendingTree:waiting", pending_tree_.get());
 }
 
 void LayerTreeHostImpl::UpdateVisibleTiles() {
-  if (tile_manager_ && tile_manager_->UpdateVisibleTiles())
+  if (tile_manager_ && tile_manager_->UpdateVisibleTiles()) {
     DidInitializeVisibleTile();
+  }
   need_to_update_visible_tiles_before_draw_ = false;
 }
 
 void LayerTreeHostImpl::ActivatePendingTree() {
   CHECK(pending_tree_);
   TRACE_EVENT_ASYNC_END0("cc", "PendingTree:waiting", pending_tree_.get());
 
   need_to_update_visible_tiles_before_draw_ = true;
 
   active_tree_->SetRootLayerScrollOffsetDelegate(NULL);
@@ skipping 1412 matching lines @@
   swap_promise_monitor_.erase(monitor);
 }
 
 void LayerTreeHostImpl::NotifySwapPromiseMonitorsOfSetNeedsRedraw() {
   std::set<SwapPromiseMonitor*>::iterator it = swap_promise_monitor_.begin();
   for (; it != swap_promise_monitor_.end(); it++)
     (*it)->OnSetNeedsRedrawOnImpl();
 }
 
 }  // namespace cc