cc : Reland move screen space scale factor to root transform node

third_party/WebKit/Source/platform/graphics/compositing/PaintArtifactCompositor.cpp

 // Copyright 2015 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 "platform/graphics/compositing/PaintArtifactCompositor.h"
 
 #include "cc/layers/content_layer_client.h"
 #include "cc/layers/layer.h"
 #include "cc/layers/picture_layer.h"
 #include "cc/playback/display_item_list.h"
@@ skipping 435 matching lines @@
   };
   Vector<BlinkEffectAndCcIdPair> m_effectStack;
 
 #if DCHECK_IS_ON()
   HashSet<const EffectPaintPropertyNode*> m_effectNodesConverted;
   bool m_isFirstEffectEver;
 #endif
 };
 
 void PropertyTreeManager::setDeviceScaleFactor(float deviceScaleFactor) {
-  auto& rootTransformNode = *transformTree().Node(kSecondaryRootNodeId);
-  rootTransformNode.local.Scale(deviceScaleFactor, deviceScaleFactor);
+  // TODO(jaydasika): We shouldn't set ToScreeen and FromScreen of root
+  // transform

[pdr., 2016/11/02 20:27:25]

Nit: the comment wrapping is a little weird here. Please rewrap to something
like:

// TODO(jaydasika): We shouldn't set ToScreeen and FromScreen of root
// transform node here. They should be set while updating transform
// tree in cc.

[jaydasika, 2016/11/02 20:45:47]

Done.

+  // node here. They should be set while updating transform tree in cc.
+  gfx::Transform toScreen;
+  toScreen.Scale(deviceScaleFactor, deviceScaleFactor);
+  transformTree().SetToScreen(kRealRootNodeId, toScreen);
+  gfx::Transform fromScreen;
+  bool invertible = toScreen.GetInverse(&fromScreen);
+  DCHECK(invertible);

[pdr., 2016/11/02 20:27:25]

Why is invertible required now but wasn't in your previous patch?

Do we need to update ancestors_are_invertible?

[jaydasika, 2016/11/02 20:45:47]

In the previous patch, it was
if (!toScreen.GetInverse(to_screen)
  ancestors_are_invertible = false
I realized that since its just a scale matrix, inverse will always exist and so
I changed it to DCHECK (ancestors_are_invertible is initliazed to true so we
don't have to explicitly set it to true here).

+  transformTree().SetFromScreen(kRealRootNodeId, fromScreen);
+  transformTree().set_needs_update(true);
 }
 
 int PropertyTreeManager::compositorIdForTransformNode(
     const TransformPaintPropertyNode* transformNode) {
   if (!transformNode)
     return kSecondaryRootNodeId;
 
   auto it = m_transformNodeMap.find(transformNode);
   if (it != m_transformNodeMap.end())
     return it->value;
@@ skipping 296 matching lines @@
   m_contentLayerClients.clear();
   m_contentLayerClients.swap(newContentLayerClients);
 
   // Mark the property trees as having been rebuilt.
   layerTree->property_trees()->sequence_number = kPropertyTreeSequenceNumber;
   layerTree->property_trees()->needs_rebuild = false;
   layerTree->property_trees()->ResetCachedData();
 }
 
 }  // namespace blink