Generate scroll/clip display item hierarchy for SPv2

Source/core/paint/LayerFixedPositionRecorder.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 "config.h"
 #include "core/paint/LayerFixedPositionRecorder.h"
 
 #include "core/layout/LayoutBoxModelObject.h"
 #include "platform/RuntimeEnabledFeatures.h"
 #include "platform/graphics/GraphicsContext.h"
 #include "platform/graphics/paint/DisplayItemList.h"
-#include "platform/graphics/paint/FixedPositionContainerDisplayItem.h"
 #include "platform/graphics/paint/FixedPositionDisplayItem.h"
 
 namespace blink {
 
-LayerFixedPositionRecorder::LayerFixedPositionRecorder(GraphicsContext& graphicsContext, const LayoutBoxModelObject& layoutObject)
+LayerFixedPositionRecorder::LayerFixedPositionRecorder(GraphicsContext& graphicsContext, const LayoutBoxModelObject& layoutObject, const LayoutBoxModelObject& anchor)
     : m_graphicsContext(graphicsContext)
     , m_layoutObject(layoutObject)
-    , m_isFixedPosition(layoutObject.style()->position() == FixedPosition)
-    , m_isFixedPositionContainer(layoutObject.canContainFixedPositionObjects())
 {
+    ASSERT(layoutObject.style()->position() == FixedPosition);
+
     if (!RuntimeEnabledFeatures::slimmingPaintV2Enabled())
         return;
 
     if (m_graphicsContext.displayItemList()->displayItemConstructionIsDisabled())
         return;
 
-    if (m_isFixedPosition)
-        m_graphicsContext.displayItemList()->createAndAppend<BeginFixedPositionDisplayItem>(m_layoutObject);
-
-    // TODO(trchen): Adding a pair of display items on every transformed
-    // element can be expensive. Investigate whether we can optimize out some
-    // of them if applicable.
-    if (m_isFixedPositionContainer)
-        m_graphicsContext.displayItemList()->createAndAppend<BeginFixedPositionContainerDisplayItem>(m_layoutObject);
+    m_graphicsContext.displayItemList()->createAndAppend<BeginFixedPositionDisplayItem>(m_layoutObject, anchor);
 }
 
 LayerFixedPositionRecorder::~LayerFixedPositionRecorder()
 {
     if (!RuntimeEnabledFeatures::slimmingPaintV2Enabled())
         return;
 
     if (m_graphicsContext.displayItemList()->displayItemConstructionIsDisabled())
         return;
 
-    if (m_isFixedPositionContainer) {
-        if (m_graphicsContext.displayItemList()->lastDisplayItemIsNoopBegin())
-            m_graphicsContext.displayItemList()->removeLastDisplayItem();
-        else
-            m_graphicsContext.displayItemList()->createAndAppend<EndFixedPositionDisplayItem>(m_layoutObject);
-    }
-
-    if (m_isFixedPosition) {
-        if (m_graphicsContext.displayItemList()->lastDisplayItemIsNoopBegin())
-            m_graphicsContext.displayItemList()->removeLastDisplayItem();
-        else
-            m_graphicsContext.displayItemList()->createAndAppend<EndFixedPositionDisplayItem>(m_layoutObject);
-    }
+    if (m_graphicsContext.displayItemList()->lastDisplayItemIsNoopBegin())
+        m_graphicsContext.displayItemList()->removeLastDisplayItem();
+    else
+        m_graphicsContext.displayItemList()->createAndAppend<EndFixedPositionDisplayItem>(m_layoutObject);
 }
 
 } // namespace blink