Have srcset respond to viewport changes

Source/core/html/HTMLImageElement.h

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  * Copyright (C) 2004, 2008, 2010 Apple Inc. All rights reserved.
  * Copyright (C) 2010 Google Inc. All rights reserved.
  *
  * 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 HTMLImageElement_h
 #define HTMLImageElement_h
 
+#include "core/frame/ViewportChangeNotifier.h"
 #include "core/html/HTMLElement.h"
 #include "core/html/HTMLImageLoader.h"
 #include "core/html/canvas/CanvasImageSource.h"
 #include "platform/graphics/GraphicsTypes.h"
 #include "wtf/WeakPtr.h"
 
 namespace WebCore {
 
 class HTMLFormElement;
 class ImageCandidate;
@@ skipping 57 matching lines @@
     virtual const KURL& sourceURL() const OVERRIDE;
 
     // public so that HTMLPictureElement can call this as well.
     void selectSourceURL(ImageLoader::UpdateFromElementBehavior);
 protected:
     explicit HTMLImageElement(Document&, HTMLFormElement* = 0, bool createdByParser = false);
 
     virtual void didMoveToNewDocument(Document& oldDocument) OVERRIDE;
 
 private:
+    class ImageViewportChangeListener FINAL : public ViewportChangeListener {

[esprehn, 2014/07/14 08:39:50]

Why is the mediaQuery thing not handling this directly?

+    public:
+        static PassRefPtrWillBeRawPtr<ImageViewportChangeListener> create(HTMLImageElement* element)
+        {
+            return adoptRefWillBeNoop(new ImageViewportChangeListener(element));
+        }
+
+        virtual void viewportChanged() OVERRIDE
+        {
+            // Re-selecting the source URL in order to pick a more fitting resource
+            // And update the image's intrinsic dimensions when the viewport changes.
+            // Picking of a better fitting resource is UA dependant, not spec required.
+            m_element->selectSourceURL(ImageLoader::UpdateForce);
+        }
+
+        explicit ImageViewportChangeListener(HTMLImageElement* element)
+            : m_element(element)
+        {
+            ASSERT(element);
+        }
+
+        void trace(Visitor* visitor)

[sof, 2014/07/14 20:38:09]

This is an OVERRIDE (of ViewportChangeListener::trace()). Move the definition of
it into the .cpp file and manually delegate the trace() --

void trace(Visitor* visitor)
{
    visitor->trace(m_element);
    ViewportChangeListener::trace(visitor);
}

+        {
+            visitor->trace(m_element);
+        }
+
+    private:
+        RawPtrWillBeMember<HTMLImageElement> m_element;
+    };
+
     virtual bool areAuthorShadowsAllowed() const OVERRIDE { return false; }
 
     virtual void parseAttribute(const QualifiedName&, const AtomicString&) OVERRIDE;
     virtual bool isPresentationAttribute(const QualifiedName&) const OVERRIDE;
     virtual void collectStyleForPresentationAttribute(const QualifiedName&, const AtomicString&, MutableStylePropertySet*) OVERRIDE;
 
     virtual void attach(const AttachContext& = AttachContext()) OVERRIDE;
     virtual RenderObject* createRenderer(RenderStyle*) OVERRIDE;
 
     virtual bool canStartSelection() const OVERRIDE;
@@ skipping 20 matching lines @@
 #if ENABLE(OILPAN)
     Member<HTMLFormElement> m_form;
 #else
     WeakPtr<HTMLFormElement> m_form;
 #endif
     CompositeOperator m_compositeOperator;
     AtomicString m_bestFitImageURL;
     float m_imageDevicePixelRatio;
     bool m_formWasSetByParser;
     bool m_elementCreatedByParser;
+    // Intrinsic sizing is viewport dependant if the 'w' descriptor was used for the picked resource.
+    bool m_intrinsicSizingViewportDependant;
+    // Effective size is viewport dependant if the sizes attribute's effective size used v* length units.
+    bool m_effectiveSizeViewportDependant;
+    RefPtrWillBeMember<ImageViewportChangeListener> m_viewportListener;

[esprehn, 2014/07/14 08:39:50]

I don't think we want to make every <img> bigger like this.

 };
 
 } //namespace
 
 #endif