Rewrite blink->cc scroll offset logic for SPV2

third_party/WebKit/Source/platform/graphics/compositing/PropertyTreeManager.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/PropertyTreeManager.h"
 
 #include "cc/layers/layer.h"
 #include "cc/trees/clip_node.h"
 #include "cc/trees/effect_node.h"
 #include "cc/trees/property_tree.h"
@@ skipping 254 matching lines @@
       scrollNode->userScrollableVertical();
   compositorNode.transform_id =
       ensureCompositorTransformNode(scrollNode->scrollOffsetTranslation());
   compositorNode.main_thread_scrolling_reasons =
       scrollNode->mainThreadScrollingReasons();
 
   auto result = m_scrollNodeMap.set(scrollNode, id);
   DCHECK(result.isNewEntry);
   scrollTree().set_needs_update(true);
 
+  // Blink creates a 2d transform node just for scroll offset whereas cc's
+  // transform node has a special scroll offset field. To handle this we
+  // adjust the compositor transform node to remove the 2d scroll translation
+  // and instead set a scroll offset.
+  cc::TransformNode& compositorTransformNode =
+      *transformTree().Node(compositorNode.transform_id);
+  DCHECK(compositorTransformNode.local.IsIdentityOr2DTranslation());
+  compositorTransformNode.local.MakeIdentity();
+  auto* scrollOffsetTransform = scrollNode->scrollOffsetTranslation();
+  auto scrollOffset = scrollOffsetTransform->matrix().to2DTranslation();
+  compositorTransformNode.scroll_offset =
+      gfx::ScrollOffset(-scrollOffset.width(), -scrollOffset.height());
+  compositorTransformNode.scrolls = true;
+
   return id;
 }
 
-void PropertyTreeManager::updateScrollOffset(int layerId, int scrollId) {
-  cc::ScrollNode& scrollNode = *scrollTree().Node(scrollId);
-  cc::TransformNode& transformNode =
-      *transformTree().Node(scrollNode.transform_id);
-
-  transformNode.scrolls = true;
-
-  // Blink creates a 2d transform node just for scroll offset whereas cc's
-  // transform node has a special scroll offset field. To handle this we
-  // adjust cc's transform node to remove the 2d scroll translation and
-  // let the cc scroll tree update the cc scroll offset.
-  DCHECK(transformNode.local.IsIdentityOr2DTranslation());
-  auto offset = transformNode.local.To2dTranslation();
-  transformNode.local.MakeIdentity();
-  scrollTree().SetScrollOffset(layerId,

[ajuma, 2017/01/20 21:35:48]

With this removed, is the scroll offset getting set on the scroll tree at all?
(If not, I'd expect main-thread-driven scrolling to work, but compositor-driven
scrolling to be broken.)

-                               gfx::ScrollOffset(-offset.x(), -offset.y()));
-  scrollTree().set_needs_update(true);
-}
-
 int PropertyTreeManager::switchToEffectNode(
     const EffectPaintPropertyNode& nextEffect) {
   const EffectPaintPropertyNode* ancestor =
       GeometryMapper::lowestCommonAncestor(currentEffectNode(), &nextEffect);
   DCHECK(ancestor) << "Malformed effect tree. All nodes must be descendant of "
                       "EffectPaintPropertyNode::root().";
   while (currentEffectNode() != ancestor)
     m_effectStack.pop_back();
 
   // Now the current effect is the lowest common ancestor of previous effect
@@ skipping 72 matching lines @@
   m_effectStack.push_back(BlinkEffectAndCcIdPair{nextEffect, effectNode.id});
 
   dummyLayer->set_property_tree_sequence_number(kPropertyTreeSequenceNumber);
   dummyLayer->SetTransformTreeIndex(kSecondaryRootNodeId);
   dummyLayer->SetClipTreeIndex(outputClipId);
   dummyLayer->SetEffectTreeIndex(effectNode.id);
   dummyLayer->SetScrollTreeIndex(kRealRootNodeId);
 }
 
 }  // namespace blink