Document reflection

third_party/WebKit/Source/core/layout/LayoutReplica.h

 /*
  * Copyright (C) 2008 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
@@ skipping 15 matching lines @@
  * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */
 
 #ifndef LayoutReplica_h
 #define LayoutReplica_h
 
 #include "core/layout/LayoutBox.h"
 
 namespace blink {
 
+// LayoutReplica is a synthetic object used to represent reflections.
+// https://www.webkit.org/blog/182/css-reflections/
+//
+// The object is part of the layout tree, however it is not fully inserted into
+// it: LayoutReplica::parent() will return the right information but the
+// parent's children() don't know about the LayoutReplica.
+// Note that its PaintLayer is fully inserted into the PaintLayer tree, which
+// requires some special casing in the painting code (e.g. in
+// PaintLayerStackingNode).
+//
+// LayoutReplica's parent() is the object with the -webkit-box-reflect.
+// LayoutReplica inherits its style from its parent() but also have an extra
+// 'transform' to paint the reflection correctly. This is done by
+// PaintLayerReflectionInfo.
+//
+// The object is created and managed by PaintLayerReflectionInfo. Also all of
+// its operations happen through PaintLayerReflectionInfo (e.g. layout, style
+// updates, ...).
+//
+// This class is a big hack. The original intent for it is unclear but has to do
+// with implementing the correct painting of reflection. It may be to apply a
+// 'transform' and offset during painting.
 class LayoutReplica final : public LayoutBox {
 public:
     static LayoutReplica* createAnonymous(Document*);
     ~LayoutReplica() override;
 
     const char* name() const override { return "LayoutReplica"; }
 
     PaintLayerType layerTypeRequired() const override { return NormalPaintLayer; }
 
     void layout() override;
 
     void paint(const PaintInfo&, const LayoutPoint&) const override;
 
 private:
     LayoutReplica();
 
     bool isOfType(LayoutObjectType type) const override { return type == LayoutObjectReplica || LayoutBox::isOfType(type); }
     void computePreferredLogicalWidths() override;
 
 };
 
 } // namespace blink
 
 #endif // LayoutReplica_h