Refactor PaintLayer location and offset calculation especially for floats

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

 /*
  * Copyright (C) 2003, 2009, 2012 Apple Inc. All rights reserved.
  * Copyright (C) 2013 Intel Corporation. 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 319 matching lines @@
   bool hasVisibleBoxDecorations() const;
   // True if this layer container layoutObjects that paint.
   bool hasNonEmptyChildLayoutObjects() const;
 
   // Will ensure that isAllScrollingContentComposited() is up to date.
   void updateScrollingStateAfterCompositingChange();
   bool isAllScrollingContentComposited() const {
     return m_isAllScrollingContentComposited;
   }
 
-  // Gets the ancestor layer that serves as the containing block of this layer.
-  // This is either another out of flow positioned layer, or one that contains
-  // paint.  If |ancestor| is specified, |*skippedAncestor| will be set to true
-  // if |ancestor| is found in the ancestry chain between this layer and the
+  // Gets the ancestor layer that serves as the containing block (in the sense
+  // of LayoutObject::container() instead of LayoutObject::containingBlock())
+  // of this layer. Normally the parent layer is the containing layer, except
+  // for out of flow positioned, floating and multicol spanner layers whose
+  // parent layer might not be the containing block.

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

I think "might not be the containing block" is incorrect. "might not be the
parent"?

[Xianzhu, 2017/01/25 22:14:10]

I think it's correct, but may be confusing. Would like to change it to "...whose
containing layer might be an ancestor of the parent layer".

[chrishtr, 2017/01/27 00:36:22]

Oh. You're saying parent() != container() in some cases. I thought you were
saying something else.

Your rephrasing sounds good to me.

+  // If |ancestor| is specified, |*skippedAncestor| will be set to true if
+  // |ancestor| is found in the ancestry chain between this layer and the
   // containing block layer; if not found, it will be set to false. Either both
   // |ancestor| and |skippedAncestor| should be nullptr, or none of them should.
-  PaintLayer* containingLayerForOutOfFlowPositioned(
-      const PaintLayer* ancestor = nullptr,
-      bool* skippedAncestor = nullptr) const;
+  PaintLayer* containingLayer(const PaintLayer* ancestor = nullptr,
+                              bool* skippedAncestor = nullptr) const;
 
   bool isPaintInvalidationContainer() const;
 
   // Do *not* call this method unless you know what you are dooing. You probably
   // want to call enclosingCompositingLayerForPaintInvalidation() instead.
   // If includeSelf is true, may return this.
   PaintLayer* enclosingLayerWithCompositedLayerMapping(IncludeSelfOrNot) const;
 
   // Returns the enclosing layer root into which this layer paints, inclusive of
   // this one. Note that the enclosing layer may or may not have its own
@@ skipping 841 matching lines @@
   unsigned m_hasRootScrollerAsDescendant : 1;
 
   LayoutBoxModelObject* m_layoutObject;
 
   PaintLayer* m_parent;
   PaintLayer* m_previous;
   PaintLayer* m_next;
   PaintLayer* m_first;
   PaintLayer* m_last;
 
-  // Our (x,y) coordinates are in our parent layer's coordinate space.
+  // Our (x,y) coordinates are in our containing layer's coordinate space.
   LayoutPoint m_location;
 
   // The layer's size.
   //
   // If the associated LayoutBoxModelObject is a LayoutBox, it's its border
   // box. Otherwise, this is the LayoutInline's lines' bounding box.
   IntSize m_size;
 
   // Cached normal flow values for absolute positioned elements with static
   // left/top values.
@@ skipping 24 matching lines @@
 
 }  // namespace blink
 
 #ifndef NDEBUG
 // Outside the WebCore namespace for ease of invocation from gdb.
 CORE_EXPORT void showLayerTree(const blink::PaintLayer*);
 CORE_EXPORT void showLayerTree(const blink::LayoutObject*);
 #endif
 
 #endif  // Layer_h