LayoutState doesn't need to store both layout and pagination offset.

third_party/WebKit/Source/core/layout/LayoutState.cpp

 /*
  * Copyright (C) 2007 Apple Inc.  All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 42 matching lines @@
     : m_containingBlockLogicalWidthChanged(containingBlockLogicalWidthChanged),
       m_next(layoutObject.view()->layoutState()),
       m_layoutObject(layoutObject) {
   if (layoutObject.isLayoutFlowThread())
     m_flowThread = toLayoutFlowThread(&layoutObject);
   else if (!layoutObject.isOutOfFlowPositioned())
     m_flowThread = m_next->flowThread();
   else
     m_flowThread = nullptr;
   layoutObject.view()->pushLayoutState(*this);
+  m_heightOffsetForTableHeaders = m_next->heightOffsetForTableHeaders();
+
+  if (pageLogicalHeight || layoutObject.isLayoutFlowThread()) {
+    // Entering a new pagination context.
+    m_pageLogicalHeight = pageLogicalHeight;
+    m_pageLogicalHeightChanged = pageLogicalHeightChanged;
+    m_paginationOffset = LayoutSize();
+    m_isPaginated = true;
+    return;
+  }
+
+  // Disable pagination for objects we don't support. For now this includes
+  // overflow:scroll/auto, inline blocks and writing mode roots. Additionally,
+  // pagination inside SVG is not allowed.
+  if (layoutObject.getPaginationBreakability() == LayoutBox::ForbidBreaks ||
+      (m_layoutObject.isSVG() && !m_layoutObject.isSVGRoot())) {
+    m_flowThread = nullptr;
+    m_pageLogicalHeight = LayoutUnit();
+    m_pageLogicalHeightChanged = false;
+    m_isPaginated = false;
+    return;
+  }
+
+  // Propagate the old page height and offset down.
+  m_pageLogicalHeight = m_next->m_pageLogicalHeight;
+  m_pageLogicalHeightChanged = m_next->m_pageLogicalHeightChanged;
+
+  m_isPaginated = m_pageLogicalHeight || m_flowThread;
+  if (!m_isPaginated)
+    return;
+
+  // Now adjust the pagination offset, so that we can easily figure out how far
+  // away we are from the start of the pagination context.
+  m_paginationOffset = m_next->m_paginationOffset;
   bool fixed = layoutObject.isOutOfFlowPositioned() &&
                layoutObject.style()->position() == FixedPosition;
-  if (fixed) {
-    // FIXME: This doesn't work correctly with transforms.
-    FloatPoint fixedOffset =
-        layoutObject.view()->localToAbsolute(FloatPoint(), IsFixed);
-    m_layoutOffset = LayoutSize(fixedOffset.x(), fixedOffset.y()) + offset;
-  } else {
-    m_layoutOffset = m_next->m_layoutOffset + offset;
-  }
-  m_heightOffsetForTableHeaders = m_next->heightOffsetForTableHeaders();
-
-  if (layoutObject.isOutOfFlowPositioned() && !fixed) {
-    if (LayoutObject* container = layoutObject.container()) {
-      if (container->style()->hasInFlowPosition() &&
-          container->isLayoutInline())
-        m_layoutOffset +=
-            toLayoutInline(container)->offsetForInFlowPositionedInline(
-                layoutObject);
-    }
-  }
-  // If we establish a new page height, then cache the offset to the top of the
-  // first page. We can compare this later on to figure out what part of the
-  // page we're actually on.
-  if (pageLogicalHeight || layoutObject.isLayoutFlowThread()) {
-    m_pageLogicalHeight = pageLogicalHeight;
-    bool isFlipped = layoutObject.style()->isFlippedBlocksWritingMode();
-    m_pageOffset = LayoutSize(
-        m_layoutOffset.width() +
-            (!isFlipped
-                 ? layoutObject.borderLeft() + layoutObject.paddingLeft()
-                 : layoutObject.borderRight() + layoutObject.paddingRight()),
-        m_layoutOffset.height() +
-            (!isFlipped
-                 ? layoutObject.borderTop() + layoutObject.paddingTop()
-                 : layoutObject.borderBottom() + layoutObject.paddingBottom()));
-    m_pageLogicalHeightChanged = pageLogicalHeightChanged;
-    m_isPaginated = true;
-  } else if (m_layoutObject.isSVG() && !m_layoutObject.isSVGRoot()) {
-    // Pagination inside SVG is not allowed.
-    m_flowThread = nullptr;
-    m_pageLogicalHeightChanged = false;
-    m_isPaginated = false;
-  } else {
-    // If we don't establish a new page height, then propagate the old page
-    // height and offset down.
-    m_pageLogicalHeight = m_next->m_pageLogicalHeight;
-    m_pageLogicalHeightChanged = m_next->m_pageLogicalHeightChanged;
-    m_pageOffset = m_next->m_pageOffset;
-
-    // Disable pagination for objects we don't support. For now this includes
-    // overflow:scroll/auto, inline blocks and writing mode roots.
-    if (layoutObject.getPaginationBreakability() == LayoutBox::ForbidBreaks) {
-      m_flowThread = nullptr;
-      m_pageLogicalHeight = LayoutUnit();
-      m_isPaginated = false;
-    } else {
-      m_isPaginated = m_pageLogicalHeight || m_flowThread;
+  if (fixed)
+    return;
+  m_paginationOffset = m_next->m_paginationOffset + offset;
+  if (!layoutObject.isOutOfFlowPositioned())
+    return;
+  if (LayoutObject* container = layoutObject.container()) {
+    if (container->style()->hasInFlowPosition() &&
+        container->isLayoutInline()) {
+      m_paginationOffset +=
+          toLayoutInline(container)->offsetForInFlowPositionedInline(
+              layoutObject);
     }
   }
 
   // FIXME: <http://bugs.webkit.org/show_bug.cgi?id=13443> Apply control clip if
   // present.
 }
 
 LayoutState::LayoutState(LayoutObject& root)
     : m_isPaginated(false),
       m_pageLogicalHeightChanged(false),
       m_containingBlockLogicalWidthChanged(false),
       m_flowThread(nullptr),
       m_next(root.view()->layoutState()),
       m_layoutObject(root) {
   ASSERT(!m_next);
   // We'll end up pushing in LayoutView itself, so don't bother adding it.
   if (root.isLayoutView())
     return;
 
   root.view()->pushLayoutState(*this);
-
-  LayoutObject* container = root.container();
-  FloatPoint absContentPoint =
-      container->localToAbsolute(FloatPoint(), UseTransforms);
-  m_layoutOffset = LayoutSize(absContentPoint.x(), absContentPoint.y());
 }
 
 LayoutState::~LayoutState() {
   if (m_layoutObject.view()->layoutState()) {
     ASSERT(m_layoutObject.view()->layoutState() == this);
     m_layoutObject.view()->popLayoutState();
   }
 }
 
 LayoutUnit LayoutState::pageLogicalOffset(
     const LayoutBox& child,
     const LayoutUnit& childLogicalOffset) const {
   if (child.isHorizontalWritingMode())
-    return m_layoutOffset.height() + childLogicalOffset - m_pageOffset.height();
-  return m_layoutOffset.width() + childLogicalOffset - m_pageOffset.width();
+    return m_paginationOffset.height() + childLogicalOffset;
+  return m_paginationOffset.width() + childLogicalOffset;
 }
 
 }  // namespace blink