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.
@@ skipping 16 matching lines @@
 #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;
+class MediaQueryList;
 
 class HTMLImageElement FINAL : public HTMLElement, public CanvasImageSource {
 public:
+    class Listener;
+
     static PassRefPtrWillBeRawPtr<HTMLImageElement> create(Document&);
     static PassRefPtrWillBeRawPtr<HTMLImageElement> create(Document&, HTMLFormElement*, bool createdByParser);
     static PassRefPtrWillBeRawPtr<HTMLImageElement> createForJSConstructor(Document&, int width, int height);
 
     virtual ~HTMLImageElement();
     virtual void trace(Visitor*) OVERRIDE;
 
     int width(bool ignorePendingStylesheets = false);
     int height(bool ignorePendingStylesheets = false);
 
@@ skipping 72 matching lines @@
     virtual void removedFrom(ContainerNode*) OVERRIDE;
     virtual bool shouldRegisterAsNamedItem() const OVERRIDE { return true; }
     virtual bool shouldRegisterAsExtraNamedItem() const OVERRIDE { return true; }
     virtual bool isInteractiveContent() const OVERRIDE;
     virtual Image* imageContents() OVERRIDE;
 
     void resetFormOwner();
     ImageCandidate findBestFitImageFromPictureParent();
     void setBestFitURLAndDPRFromImageCandidate(const ImageCandidate&);
     HTMLImageLoader& imageLoader() const { return *m_imageLoader; }
+    void notifyMediaQueryChanged();
+    void createMediaQueryListIfDoesNotExist();
 
     OwnPtrWillBeMember<HTMLImageLoader> m_imageLoader;
 #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<Listener> m_listener;

[sof, 2014/07/15 10:27:30]

Whenever a traceable Member is added to a class, you need to trace() it in the
class' trace() method. Both the Members here aren't traced.

+    RefPtrWillBeMember<MediaQueryList> m_mediaQueryList;
 };

[Yoav Weiss, 2014/07/15 09:46:31]

If the extra memory on HTMLImageElement is an issue here (considering that
m_listener and m_mediaQueryList) are created only for images that need them, I'd
appreciate some advice on how to reduce that footprint.
Possible optimizations include:
* Instruct the compiler to pack the 4 booleans on HTMLImageElement.
* Create a single raw pointer that would hold both m_listener and
m_mediaQueryList. (Note that they are created only when they are actually
needed, so when the image is viewport dependent)
* Avoid storing m_mediaQueryList and create it each time the source is
recalculated.

 
 } //namespace
 
 #endif