Move toClipPath to SVGGeometryElement.

Source/core/svg/SVGUseElement.h

 /*
  * Copyright (C) 2004, 2005, 2006, 2007, 2008 Nikolas Zimmermann <zimmermann@kde.org>
  * Copyright (C) 2004, 2005, 2006, 2007 Rob Buis <buis@kde.org>
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
  * License as published by the Free Software Foundation; either
  * version 2 of the License, or (at your option) any later version.
  *
  * This library is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  * Library General Public License for more details.
  *
  * You should have received a copy of the GNU Library General Public License
  * along with this library; see the file COPYING.LIB.  If not, write to
  * the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
  * Boston, MA 02110-1301, USA.
  */
 
 #ifndef SVGUseElement_h
 #define SVGUseElement_h
 
 #include "core/events/EventSender.h"
 #include "core/fetch/DocumentResource.h"
 #include "core/svg/SVGAnimatedLength.h"
+#include "core/svg/SVGGeometryElement.h"
 #include "core/svg/SVGGraphicsElement.h"
 #include "core/svg/SVGURIReference.h"
 #include "platform/heap/Handle.h"
 
 namespace blink {
 
 typedef EventSender<SVGUseElement> SVGUseEventSender;
 
 class SVGUseElement final : public SVGGraphicsElement,
                             public SVGURIReference,
                             public DocumentResourceClient {
     DEFINE_WRAPPERTYPEINFO();
     WILL_BE_USING_GARBAGE_COLLECTED_MIXIN(SVGUseElement);
 public:
     static PassRefPtrWillBeRawPtr<SVGUseElement> create(Document&);
     virtual ~SVGUseElement();
 
     void invalidateShadowTree();
 
-    LayoutObject* layoutObjectClipChild() const;
+    SVGGeometryElement* layoutObjectClipChild(Path&) const;

[pdr., 2015/06/09 05:15:58]

Sadness... the original code is worse than I expected and has real bugs. This
may require many patches and I understand if you'd like to work on something
else. If you're up for it, I'll sketch out a good first patch below:

SVGClipPainter::applyClippingToContext has two "modes":
1) A "path-only" approach (tryPathOnlyClipping) which calls
SVGUseElement::toClipPath
2) A mask approach (drawClipMaskContent) which ends up calling
SVGUseElement::layoutObjectClipChild
Our goal is to unify these so they use the same code. The following might be a
good design:

const SVGGraphicsElement* SVGUseElement::targetGraphicsElementForClipping();
You should write a comment in the header file describing what we are returning
and why. You may want to reference the spec, particularly this part: "If a <use>
element is a child of a clipPath element, it must directly reference <path>,
<text> or basic shapes elements." You probably want to actually check for the
allowed references too... something like isSVGTextElement() || isSVGTSpanElement
|| isSVGGeometryElement. You may also want to mention how we will return null if
an allowed element is not available.

Lets leave SVGUseElement::toClipPath for now, but make it non-virtual. Also
change the implementation to call our new targetGraphicsElementForClipping
function, but make sure to check isSVGGeometryElement because path-only clipping
doesn't work for text.

[hyunjunekim2, 2015/06/10 14:00:42]

I will try again for your advice.

 
     SVGAnimatedLength* x() const { return m_x.get(); }
     SVGAnimatedLength* y() const { return m_y.get(); }
     SVGAnimatedLength* width() const { return m_width.get(); }
     SVGAnimatedLength* height() const { return m_height.get(); }
 
     virtual void buildPendingResource() override;
 
     void dispatchPendingEvent(SVGUseEventSender*);
 
     DECLARE_VIRTUAL_TRACE();
 
 private:
     explicit SVGUseElement(Document&);
 
     virtual bool isPresentationAttribute(const QualifiedName&) const override;
     virtual void collectStyleForPresentationAttribute(const QualifiedName&, const AtomicString&, MutableStylePropertySet*) override;
     virtual bool isPresentationAttributeWithSVGDOM(const QualifiedName&) const override;
 
     virtual bool isStructurallyExternal() const override { return !hrefString().isNull() && isExternalURIReference(hrefString(), document()); }
 
     virtual InsertionNotificationRequest insertedInto(ContainerNode*) override;
     virtual void removedFrom(ContainerNode*) override;
 
     virtual void svgAttributeChanged(const QualifiedName&) override;
 
     virtual LayoutObject* createLayoutObject(const ComputedStyle&) override;
-    virtual void toClipPath(Path&) override;
 
     void clearResourceReferences();
     void buildShadowAndInstanceTree(SVGElement* target);
 
     void scheduleShadowTreeRecreation();
     virtual bool haveLoadedRequiredResources() override { return !isStructurallyExternal() || m_haveFiredLoadEvent; }
 
     virtual bool selfHasRelativeLengths() const override;
 
     // Instance tree handling
@@ skipping 20 matching lines @@
 
     bool m_haveFiredLoadEvent;
     bool m_needsShadowTreeRecreation;
     RefPtrWillBeMember<SVGElement> m_targetElementInstance;
     ResourcePtr<DocumentResource> m_resource;
 };
 
 } // namespace blink
 
 #endif // SVGUseElement_h