Refactor PaintLayer location and offset calculation especially for floats

third_party/WebKit/Source/core/paint/PaintLayer.cpp

 /*
  * Copyright (C) 2006, 2007, 2008, 2009, 2010, 2011, 2012 Apple Inc. All rights
  * reserved.
  *
  * Portions are Copyright (C) 1998 Netscape Communications Corporation.
  *
  * Other contributors:
  *   Robert O'Callahan <roc+@cs.cmu.edu>
  *   David Baron <dbaron@fas.harvard.edu>
  *   Christian Biesinger <cbiesinger@web.de>
@@ skipping 782 matching lines @@
         localPoint.moveBy(toLayoutBox(curr)->physicalLocation());
       }
       curr = curr->container();
     }
     if (curr && curr->isTableRow()) {
       // Put ourselves into the row coordinate space.
       localPoint.moveBy(-toLayoutBox(curr)->physicalLocation());
     }
   }
 
-  // Subtract our parent's scroll offset.
-  if (PaintLayer* containingLayer =
-          layoutObject()->isOutOfFlowPositioned()
-              ? containingLayerForOutOfFlowPositioned()
-              : nullptr) {
-    // For positioned layers, we subtract out the enclosing positioned layer's
-    // scroll offset.
+  if (PaintLayer* containingLayer = this->containingLayer()) {
     if (containingLayer->layoutObject()->hasOverflowClip()) {
+      // Subtract our container's scroll offset.
       IntSize offset = containingLayer->layoutBox()->scrolledContentOffset();
       localPoint -= offset;
-    }
-
-    if (containingLayer->layoutObject()->isInFlowPositioned() &&
-        containingLayer->layoutObject()->isLayoutInline()) {
+    } else if (layoutObject()->isAbsolutePositioned() &&
+               containingLayer->layoutObject()->isInFlowPositioned() &&
+               containingLayer->layoutObject()->isLayoutInline()) {
+      // Adjust offset for absolute under in-flow positioned inline.
       LayoutSize offset =
           toLayoutInline(containingLayer->layoutObject())
               ->offsetForInFlowPositionedInline(*toLayoutBox(layoutObject()));
       localPoint += offset;
     }
-  } else if (parent() && parent()->layoutObject()->hasOverflowClip()) {
-    IntSize scrollOffset = parent()->layoutBox()->scrolledContentOffset();
-    localPoint -= scrollOffset;
   }
 
   if (layoutObject()->isInFlowPositioned()) {
     LayoutSize newOffset = layoutObject()->offsetForInFlowPosition();
     if (m_rareData || !newOffset.isZero())
       ensureRareData().offsetForInFlowPosition = newOffset;
     localPoint.move(newOffset);
   } else if (m_rareData) {
     m_rareData->offsetForInFlowPosition = LayoutSize();
   }
@@ skipping 27 matching lines @@
 
   const LayoutRect borderBox = toLayoutBox(layoutObject())->borderBoxRect();
   const ComputedStyle& style = layoutObject()->styleRef();
 
   return FloatPoint(floatValueForLength(style.perspectiveOriginX(),
                                         borderBox.width().toFloat()),
                     floatValueForLength(style.perspectiveOriginY(),
                                         borderBox.height().toFloat()));
 }
 
-PaintLayer* PaintLayer::containingLayerForOutOfFlowPositioned(
-    const PaintLayer* ancestor,
-    bool* skippedAncestor) const {
+PaintLayer* PaintLayer::containingLayer(const PaintLayer* ancestor,
+                                        bool* skippedAncestor) const {
   // If we have specified an ancestor, surely the caller needs to know whether
   // we skipped it.
   DCHECK(!ancestor || skippedAncestor);
   if (skippedAncestor)
     *skippedAncestor = false;
-  if (layoutObject()->style()->position() == FixedPosition) {
+
+  LayoutObject* layoutObject = this->layoutObject();

[chrishtr, 2017/01/25 21:06:40]

Are the changes here just refactoring? It seems to change the behavior of
PaintLayer::updateLayerPosition in particular, to take into account
columnSpanAll
and other factors.

[Xianzhu, 2017/01/25 22:03:00]

This changes old lines 822-824 for floating and columnSpanAll from:
  if (parent() && parent()->layoutObject()->hasOverflowClip())
    localPoint -= parent()->layoutBox()->scrolledContentOffset();

to
  if (containingLayer && containingLayer->layoutObject()->hasOverflowClip())
    localPoint -= containingLayer->layoutBox()->scrolledContentOffset();

This seems to fix a bug in the following case (in which previously we missed
adjustment of the scroll offset of the outer div for the float div):
  <div style="overflow: scroll">
    <span style="position: relative">
      <div style="float: left"></div>
    </span>
  </div>

Will add a test case for it, and also look into columnSpanAll in the similar
situation.

+  if (layoutObject->isColumnSpanAll() ||
+      layoutObject->isFloatingWithNonContainingBlockParent()) {
+    Optional<LayoutObject::AncestorSkipInfo> skipInfo;
+    if (skippedAncestor)
+      skipInfo.emplace(ancestor->layoutObject());
+    if (auto containingBlock = layoutObject->containingBlock(
+            skippedAncestor ? &*skipInfo : nullptr)) {
+      if (skippedAncestor && skipInfo->ancestorSkipped())
+        *skippedAncestor = true;
+      return containingBlock->enclosingLayer();
+    }
+    return nullptr;
+  }
+
+  if (layoutObject->isOutOfFlowPositioned()) {
+    auto canContainThisLayer =
+        layoutObject->isFixedPositioned()
+            ? &LayoutObject::canContainFixedPositionObjects
+            : &LayoutObject::canContainAbsolutePositionObjects;
+
     PaintLayer* curr = parent();
-    while (curr && !curr->layoutObject()->canContainFixedPositionObjects()) {
+    while (curr && !(curr->layoutObject()->*canContainThisLayer)()) {
       if (skippedAncestor && curr == ancestor)
         *skippedAncestor = true;
       curr = curr->parent();
     }
-
     return curr;
   }
 
-  PaintLayer* curr = parent();
-  while (curr && !curr->layoutObject()->canContainAbsolutePositionObjects()) {
-    if (skippedAncestor && curr == ancestor)
-      *skippedAncestor = true;
-    curr = curr->parent();
-  }
-
-  return curr;
+  return parent();
 }
 
 PaintLayer* PaintLayer::enclosingTransformedAncestor() const {
   PaintLayer* curr = parent();
   while (curr && !curr->isRootLayer() && !curr->transform())
     curr = curr->parent();
 
   return curr;
 }
 
 LayoutPoint PaintLayer::computeOffsetFromTransformedAncestor() const {
   TransformState transformState(TransformState::ApplyTransformDirection,
                                 FloatPoint());
   layoutObject()->mapLocalToAncestor(
       transformAncestor() ? transformAncestor()->layoutObject() : nullptr,
       transformState, 0);
   transformState.flatten();
   return LayoutPoint(transformState.lastPlanarPoint());
 }
 
 PaintLayer* PaintLayer::compositingContainer() const {
-  if (!stackingNode()->isStacked()) {
-    // Floats have special painting order, which has complicated semantics.
-    // See the comments around FloatObject::setShouldPaint.
-    if (m_layoutObject->isFloating() && m_layoutObject->parent() &&
-        !m_layoutObject->parent()->isLayoutBlockFlow())
-      return m_layoutObject->containingBlock()->enclosingLayer();
-
-    return parent();
-  }
+  if (!stackingNode()->isStacked())
+    return containingLayer();
   if (PaintLayerStackingNode* ancestorStackingNode =
           stackingNode()->ancestorStackingContextNode())
     return ancestorStackingNode->layer();
   return nullptr;
 }
 
 bool PaintLayer::isPaintInvalidationContainer() const {
   return compositingState() == PaintsIntoOwnBacking ||
          compositingState() == PaintsIntoGroupedBacking;
 }
@@ skipping 461 matching lines @@
 }
 
 // Returns the layer reached on the walk up towards the ancestor.
 static inline const PaintLayer* accumulateOffsetTowardsAncestor(
     const PaintLayer* layer,
     const PaintLayer* ancestorLayer,
     LayoutPoint& location) {
   DCHECK(ancestorLayer != layer);
 
   const LayoutBoxModelObject* layoutObject = layer->layoutObject();
-  EPosition position = layoutObject->style()->position();
 
-  if (position == FixedPosition &&
+  if (layoutObject->isFixedPositioned() &&
       (!ancestorLayer || ancestorLayer == layoutObject->view()->layer())) {
     // If the fixed layer's container is the root, just add in the offset of the
     // view. We can obtain this by calling localToAbsolute() on the LayoutView.
     FloatPoint absPos = layoutObject->localToAbsolute();
     location += LayoutSize(absPos.x(), absPos.y());
     return ancestorLayer;
   }
 
-  PaintLayer* parentLayer = nullptr;
-  if (position == AbsolutePosition || position == FixedPosition ||
-      (layoutObject->isFloating() && layoutObject->parent() &&
-       !layoutObject->parent()->isLayoutBlockFlow())) {
-    bool foundAncestorFirst = false;
-    if (layoutObject->isFloating()) {
-      Optional<LayoutObject::AncestorSkipInfo> skipInfo;
-      if (ancestorLayer)
-        skipInfo.emplace(ancestorLayer->layoutObject());
-      if (auto* containingBlock = layoutObject->containingBlock(
-              ancestorLayer ? &*skipInfo : nullptr)) {
-        parentLayer = containingBlock->enclosingLayer();
-        foundAncestorFirst = ancestorLayer && skipInfo->ancestorSkipped();
-      }
-    } else {
-      parentLayer = layer->containingLayerForOutOfFlowPositioned(
-          ancestorLayer, &foundAncestorFirst);
-    }
+  bool foundAncestorFirst;
+  PaintLayer* containingLayer =
+      layer->containingLayer(ancestorLayer, &foundAncestorFirst);
 
-    if (foundAncestorFirst) {
-      // Found ancestorLayer before the container of the out-of-flow object, so
-      // compute offset of both relative to the container and subtract.
+  if (foundAncestorFirst) {
+    // Found ancestorLayer before the containing layer, so compute offset of
+    // both relative to the container and subtract.
+    LayoutPoint thisCoords;
+    layer->convertToLayerCoords(containingLayer, thisCoords);
 
-      LayoutPoint thisCoords;
-      layer->convertToLayerCoords(parentLayer, thisCoords);
+    LayoutPoint ancestorCoords;
+    ancestorLayer->convertToLayerCoords(containingLayer, ancestorCoords);
 
-      LayoutPoint ancestorCoords;
-      ancestorLayer->convertToLayerCoords(parentLayer, ancestorCoords);
-
-      location += (thisCoords - ancestorCoords);
-      return ancestorLayer;
-    }
-  } else if (layoutObject->isColumnSpanAll()) {
-    LayoutBlock* multicolContainer = layoutObject->containingBlock();
-    DCHECK(toLayoutBlockFlow(multicolContainer)->multiColumnFlowThread());
-    parentLayer = multicolContainer->layer();
-    DCHECK(parentLayer);
-  } else {
-    parentLayer = layer->parent();
+    location += (thisCoords - ancestorCoords);
+    return ancestorLayer;
   }
 
-  if (!parentLayer)
+  if (!containingLayer)
     return nullptr;
 
   location += layer->location();
-  return parentLayer;
+  return containingLayer;
 }
 
 void PaintLayer::convertToLayerCoords(const PaintLayer* ancestorLayer,
                                       LayoutPoint& location) const {
   if (ancestorLayer == this)
     return;
 
   const PaintLayer* currLayer = this;
   while (currLayer && currLayer != ancestorLayer)
     currLayer =
@@ skipping 1758 matching lines @@
 }
 
 void showLayerTree(const blink::LayoutObject* layoutObject) {
   if (!layoutObject) {
     LOG(INFO) << "Cannot showLayerTree. Root is (nil)";
     return;
   }
   showLayerTree(layoutObject->enclosingLayer());
 }
 #endif