cc: Don't activate pending tree until all tiles are ready

cc/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/layer_tree_host_impl.h"
 
 #include <algorithm>
 
 #include "base/basictypes.h"
 #include "base/debug/trace_event.h"
@@ skipping 990 matching lines @@
     m_client->onCanDrawStateChanged(canDraw());
     m_client->onHasPendingTreeStateChanged(pendingTree());
 }
 
 void LayerTreeHostImpl::activatePendingTreeIfNeeded()
 {
     if (!pendingTree())
         return;
 
     int total_pending = m_tileManager->GetTilesInBinCount(NOW_BIN, PENDING_TREE);
+    int drawable_pending = m_tileManager->GetDrawableTilesInBinCount(NOW_BIN, PENDING_TREE);
     int total_active = m_tileManager->GetTilesInBinCount(NOW_BIN, ACTIVE_TREE);

[nduca, 2013/01/05 04:51:49]

The more I stare at this, the more I think we should give per-layer activation a
try...

-    int drawable_pending = m_tileManager->GetDrawableTilesInBinCount(NOW_BIN, PENDING_TREE);
-    int drawable_active = m_tileManager->GetDrawableTilesInBinCount(NOW_BIN, ACTIVE_TREE);
 
-    if (total_pending && total_active) {
-        float percent_pending = drawable_pending / static_cast<float>(total_pending);
-        float percent_active = drawable_active / static_cast<float>(total_active);
-        if (percent_pending < percent_active)
-            return;
-    }
+    // It's always fine to activate to or from an empty tree.  Otherwise, only
+    // activate once all high res visible tiles are ready on the pending tree.
+    if (total_pending && total_active && total_pending != drawable_pending)
+        return;
 
-    // If there are no pending total tiles (i.e. an empty tree), we should
-    // commit immediately.  Similarly, if there are no active tree tiles.
     activatePendingTree();
 }
 
 void LayerTreeHostImpl::activatePendingTree()
 {
     CHECK(m_pendingTree);
     m_activeTree.swap(m_pendingTree);
     // TODO(enne): consider recycling this tree to prevent layer churn
     m_pendingTree.reset();
     m_client->onCanDrawStateChanged(canDraw());
@@ skipping 672 matching lines @@
     ScrollbarAnimationController* scrollbarController = layer->scrollbarAnimationController();
     double monotonicTime = (time - base::TimeTicks()).InSecondsF();
     if (scrollbarController && scrollbarController->animate(monotonicTime))
         m_client->setNeedsRedrawOnImplThread();
 
     for (size_t i = 0; i < layer->children().size(); ++i)
         animateScrollbarsRecursive(layer->children()[i], time);
 }
 
 }  // namespace cc