Use Shadow DOM to display fallback content for images

Source/core/html/HTMLImageElement.cpp

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  * Copyright (C) 2004, 2005, 2006, 2007, 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 14 matching lines @@
 
 #include "bindings/core/v8/ScriptEventListener.h"
 #include "core/CSSPropertyNames.h"
 #include "core/HTMLNames.h"
 #include "core/MediaTypeNames.h"
 #include "core/css/MediaQueryMatcher.h"
 #include "core/css/MediaValuesDynamic.h"
 #include "core/css/parser/SizesAttributeParser.h"
 #include "core/dom/Attribute.h"
 #include "core/dom/NodeTraversal.h"
+#include "core/dom/shadow/ShadowRoot.h"
 #include "core/fetch/ImageResource.h"
 #include "core/frame/UseCounter.h"
 #include "core/html/HTMLAnchorElement.h"
 #include "core/html/HTMLCanvasElement.h"
 #include "core/html/HTMLFormElement.h"
+#include "core/html/HTMLImageFallbackHelper.h"
 #include "core/html/HTMLSourceElement.h"
 #include "core/html/canvas/CanvasRenderingContext.h"
 #include "core/html/parser/HTMLParserIdioms.h"
 #include "core/html/parser/HTMLSrcsetParser.h"
 #include "core/inspector/ConsoleMessage.h"
+#include "core/rendering/RenderBlockFlow.h"
 #include "core/rendering/RenderImage.h"
 #include "platform/ContentType.h"
 #include "platform/MIMETypeRegistry.h"
 #include "platform/RuntimeEnabledFeatures.h"
 
 namespace blink {
 
 using namespace HTMLNames;
 
 class HTMLImageElement::ViewportChangeListener final : public MediaQueryListListener {
@@ skipping 22 matching lines @@
     RawPtrWillBeMember<HTMLImageElement> m_element;
 };
 
 HTMLImageElement::HTMLImageElement(Document& document, HTMLFormElement* form, bool createdByParser)
     : HTMLElement(imgTag, document)
     , m_imageLoader(HTMLImageLoader::create(this))
     , m_imageDevicePixelRatio(1.0f)
     , m_formWasSetByParser(false)
     , m_elementCreatedByParser(createdByParser)
     , m_intrinsicSizingViewportDependant(false)
+    , m_useFallbackContent(false)
+    , m_isFallbackImage(false)
 {
+    setHasCustomStyleCallbacks();
     if (form && form->inDocument()) {
 #if ENABLE(OILPAN)
         m_form = form;
 #else
         m_form = form->createWeakPtr();
 #endif
         m_formWasSetByParser = true;
         m_form->associate(*this);
         m_form->didAssociateByParser();
     }
@@ skipping 130 matching lines @@
         UseCounter::count(document(), UseCounter::SrcsetWDescriptor);
     } else if (!candidate.srcOrigin()) {
         UseCounter::count(document(), UseCounter::SrcsetXDescriptor);
     }
     if (renderer() && renderer()->isImage())
         toRenderImage(renderer())->setImageDevicePixelRatio(m_imageDevicePixelRatio);
 }
 
 void HTMLImageElement::parseAttribute(const QualifiedName& name, const AtomicString& value)
 {
-    if (name == altAttr) {
-        if (renderer() && renderer()->isImage())
-            toRenderImage(renderer())->updateAltText();
+    if (name == altAttr || name == titleAttr) {
+        if (userAgentShadowRoot()) {
+            Element* text = userAgentShadowRoot()->getElementById("alttext");
+            String value = altText();
+            if (text && text->textContent() != value)
+                text->setTextContent(altText());
+        }
     } else if (name == srcAttr || name == srcsetAttr || name == sizesAttr) {
         selectSourceURL(ImageLoader::UpdateIgnorePreviousError);
     } else if (name == usemapAttr) {
         setIsLink(!value.isNull());
     } else {
         HTMLElement::parseAttribute(name, value);
     }
 }
 
-const AtomicString& HTMLImageElement::altText() const
+String HTMLImageElement::altText() const
 {
     // lets figure out the alt text.. magic stuff
     // http://www.w3.org/TR/1998/REC-html40-19980424/appendix/notes.html#altgen
     // also heavily discussed by Hixie on bugzilla
     const AtomicString& alt = fastGetAttribute(altAttr);
     if (!alt.isNull())
         return alt;
     // fall back to title attribute
     return fastGetAttribute(titleAttr);
 }
@@ skipping 45 matching lines @@
         return candidate;
     }
     return ImageCandidate();
 }
 
 RenderObject* HTMLImageElement::createRenderer(RenderStyle* style)
 {
     if (style->hasContent())
         return RenderObject::createObject(this, style);
 
+    if (m_useFallbackContent)
+        return new RenderBlockFlow(this);
+
     RenderImage* image = new RenderImage(this);
     image->setImageResource(RenderImageResource::create());
     image->setImageDevicePixelRatio(m_imageDevicePixelRatio);
     return image;
 }
 
 bool HTMLImageElement::canStartSelection() const
 {
     if (shadow())
         return HTMLElement::canStartSelection();
 
     return false;
 }
 
 void HTMLImageElement::attach(const AttachContext& context)
 {
     HTMLElement::attach(context);
 
     if (renderer() && renderer()->isImage()) {
         RenderImage* renderImage = toRenderImage(renderer());
         RenderImageResource* renderImageResource = renderImage->imageResource();
         if (renderImageResource->hasImage())
             return;
 
-        // If we have no image at all because we have no src attribute, set
-        // image height and width for the alt text instead.
         if (!imageLoader().image() && !renderImageResource->cachedImage())
-            renderImage->setImageSizeForAltText();
-        else
-            renderImageResource->setImageResource(imageLoader().image());
-
+            return;
+        renderImageResource->setImageResource(imageLoader().image());
     }
 }
 
 Node::InsertionNotificationRequest HTMLImageElement::insertedInto(ContainerNode* insertionPoint)
 {
     if (!m_formWasSetByParser || NodeTraversal::highestAncestorOrSelf(*insertionPoint) != NodeTraversal::highestAncestorOrSelf(*m_form.get()))
         resetFormOwner();
     if (m_listener)
         document().mediaQueryMatcher().addViewportListener(m_listener);
 
     bool imageWasModified = false;
     if (RuntimeEnabledFeatures::pictureEnabled() && document().isActive()) {
         ImageCandidate candidate = findBestFitImageFromPictureParent();
         if (!candidate.isEmpty()) {
             setBestFitURLAndDPRFromImageCandidate(candidate);
             imageWasModified = true;
         }
     }
 
     // If we have been inserted from a renderer-less document,
     // our loader may have not fetched the image, so do it now.
     if ((insertionPoint->inDocument() && !imageLoader().image()) || imageWasModified)
-        imageLoader().updateFromElement(ImageLoader::UpdateNormal, m_elementCreatedByParser ? ImageLoader::ForceLoadImmediately : ImageLoader::LoadNormally);
+        imageLoader().updateFromElement(ImageLoader::UpdateNormal);
 
     return HTMLElement::insertedInto(insertionPoint);
 }
 
 void HTMLImageElement::removedFrom(ContainerNode* insertionPoint)
 {
     if (!m_form || NodeTraversal::highestAncestorOrSelf(*m_form.get()) != NodeTraversal::highestAncestorOrSelf(*this))
         resetFormOwner();
     if (m_listener)
         document().mediaQueryMatcher().removeViewportListener(m_listener);
@@ skipping 258 matching lines @@
             effectiveSize = parser.length();
         }
         ImageCandidate candidate = bestFitSourceForImageAttributes(document().devicePixelRatio(), effectiveSize, fastGetAttribute(srcAttr), fastGetAttribute(srcsetAttr), &document());
         setBestFitURLAndDPRFromImageCandidate(candidate);
     }
     if (m_intrinsicSizingViewportDependant && !m_listener) {
         m_listener = ViewportChangeListener::create(this);
         document().mediaQueryMatcher().addViewportListener(m_listener);
     }
     imageLoader().updateFromElement(behavior);
+
+    if (imageLoader().image() || (imageLoader().hasPendingActivity() && !imageSourceURL().isEmpty()))
+        ensurePrimaryContent();
+    else
+        ensureFallbackContent();
 }
 
 const KURL& HTMLImageElement::sourceURL() const
 {
     return cachedImage()->response().url();
 }
 
+void HTMLImageElement::didAddUserAgentShadowRoot(ShadowRoot&)
+{
+    HTMLImageFallbackHelper::createAltTextShadowTree(*this);
 }
+
+void HTMLImageElement::ensureFallbackContent()
+{
+    if (m_useFallbackContent || m_isFallbackImage)
+        return;
+    setUseFallbackContent();
+    reattachFallbackContent();
+}
+
+void HTMLImageElement::ensurePrimaryContent()
+{
+    if (!m_useFallbackContent)
+        return;
+    m_useFallbackContent = false;
+    reattachFallbackContent();
+}
+
+void HTMLImageElement::reattachFallbackContent()
+{
+    // This can happen inside of attach() in the middle of a recalcStyle so we need to
+    // reattach synchronously here.
+    if (document().inStyleRecalc())
+        reattach();
+    else
+        lazyReattachIfAttached();
+}
+
+PassRefPtr<RenderStyle> HTMLImageElement::customStyleForRenderer()
+{
+    RefPtr<RenderStyle> newStyle = originalStyleForRenderer();
+
+    if (!m_useFallbackContent)
+        return newStyle;
+    return HTMLImageFallbackHelper::customStyleForAltText(*this, newStyle);
+}
+
+void HTMLImageElement::setUseFallbackContent()
+{
+    m_useFallbackContent = true;
+    if (document().inStyleRecalc())
+        return;
+    ensureUserAgentShadowRoot();
+}
+}