third_party/WebKit/Source/core/html/HTMLImageFallbackHelper.cpp

   1 // Copyright 2014 The Chromium Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style license that can be
   3 // found in the LICENSE file.
   4
   5 #include "config.h"
   6 #include "core/html/HTMLImageFallbackHelper.h"
   7
   8 #include "core/HTMLNames.h"
   9 #include "core/InputTypeNames.h"
  10 #include "core/dom/ElementRareData.h"
  11 #include "core/dom/Text.h"
  12 #include "core/dom/shadow/ShadowRoot.h"
  13 #include "core/fetch/ImageResource.h"
  14 #include "core/html/HTMLDivElement.h"
  15 #include "core/html/HTMLElement.h"
  16 #include "core/html/HTMLImageElement.h"
  17 #include "core/html/HTMLImageLoader.h"
  18 #include "core/html/HTMLInputElement.h"
  19 #include "core/html/HTMLStyleElement.h"
  20 #include "wtf/PassOwnPtr.h"
  21 #include "wtf/text/StringBuilder.h"
  22
  23 namespace blink {
  24
  25 using namespace HTMLNames;
  26
  27 static bool noImageSourceSpecified(const Element& element)
  28 {
  29     bool noSrcSpecified = !element.hasAttribute(srcAttr) || element.getAttribute(srcAttr).isNull() || element.getAttribute(srcAttr).isEmpty();
  30     bool noSrcsetSpecified = !element.hasAttribute(srcsetAttr) || element.getAttribute(srcsetAttr).isNull() || element.getAttribute(srcsetAttr).isEmpty();
  31     return noSrcSpecified && noSrcsetSpecified;
  32 }
  33
  34 void HTMLImageFallbackHelper::createAltTextShadowTree(Element& element)
  35 {
  36     ShadowRoot& root = element.ensureUserAgentShadowRoot();
  37
  38     RefPtrWillBeRawPtr<HTMLDivElement> container = HTMLDivElement::create(element.document());
  39     root.appendChild(container);
  40     container->setAttribute(idAttr, AtomicString("alttext-container", AtomicString::ConstructFromLiteral));
  41     container->setInlineStyleProperty(CSSPropertyOverflow, CSSValueHidden);
  42     container->setInlineStyleProperty(CSSPropertyBorderWidth, 1, CSSPrimitiveValue::UnitType::Pixels);
  43     container->setInlineStyleProperty(CSSPropertyBorderStyle, CSSValueSolid);
  44     container->setInlineStyleProperty(CSSPropertyBorderColor, CSSValueSilver);
  45     container->setInlineStyleProperty(CSSPropertyDisplay, CSSValueInlineBlock);
  46     container->setInlineStyleProperty(CSSPropertyBoxSizing, CSSValueBorderBox);
  47     container->setInlineStyleProperty(CSSPropertyPadding, 1, CSSPrimitiveValue::UnitType::Pixels);
  48
  49     RefPtrWillBeRawPtr<HTMLImageElement> brokenImage = HTMLImageElement::create(element.document());
  50     container->appendChild(brokenImage);
  51     brokenImage->setIsFallbackImage();
  52     brokenImage->setAttribute(idAttr, AtomicString("alttext-image", AtomicString::ConstructFromLiteral));
  53     brokenImage->setAttribute(widthAttr, AtomicString("16", AtomicString::ConstructFromLiteral));
  54     brokenImage->setAttribute(heightAttr, AtomicString("16", AtomicString::ConstructFromLiteral));
  55     brokenImage->setAttribute(alignAttr, AtomicString("left", AtomicString::ConstructFromLiteral));
  56     brokenImage->setInlineStyleProperty(CSSPropertyMargin, 0, CSSPrimitiveValue::UnitType::Pixels);
  57
  58     RefPtrWillBeRawPtr<HTMLDivElement> altText = HTMLDivElement::create(element.document());
  59     container->appendChild(altText);
  60     altText->setAttribute(idAttr, AtomicString("alttext", AtomicString::ConstructFromLiteral));
  61     altText->setInlineStyleProperty(CSSPropertyOverflow, CSSValueHidden);
  62     altText->setInlineStyleProperty(CSSPropertyDisplay, CSSValueBlock);
  63
  64     RefPtrWillBeRawPtr<Text> text = Text::create(element.document(), toHTMLElement(element).altText());
  65     altText->appendChild(text);
  66 }
  67
  68 PassRefPtr<ComputedStyle> HTMLImageFallbackHelper::customStyleForAltText(Element& element, PassRefPtr<ComputedStyle> newStyle)
  69 {
  70     // If we have an author shadow root or have not created the UA shadow root yet, bail early. We can't
  71     // use ensureUserAgentShadowRoot() here because that would alter the DOM tree during style recalc.
  72     if (element.authorShadowRoot() || !element.userAgentShadowRoot())
  73         return newStyle;
  74
  75     Element* placeHolder = element.userAgentShadowRoot()->getElementById("alttext-container");
  76     Element* brokenImage = element.userAgentShadowRoot()->getElementById("alttext-image");
  77     // Input elements have a UA shadow root of their own. We may not have replaced it with fallback content yet.
  78     if (!placeHolder || !brokenImage)
  79         return newStyle;
  80
  81
  82     if (element.document().inQuirksMode()) {
  83         // Mimic the behaviour of the image host by setting symmetric dimensions if only one dimension is specified.
  84         if (newStyle->width().isSpecifiedOrIntrinsic() && newStyle->height().isAuto())
  85             newStyle->setHeight(newStyle->width());
  86         else if (newStyle->height().isSpecifiedOrIntrinsic() && newStyle->width().isAuto())
  87             newStyle->setWidth(newStyle->height());
  88         if (newStyle->width().isSpecifiedOrIntrinsic() && newStyle->height().isSpecifiedOrIntrinsic()) {
  89             placeHolder->setInlineStyleProperty(CSSPropertyVerticalAlign, CSSValueBaseline);
  90         }
  91     }
  92
  93     // If the image has specified dimensions allow the alt-text container expand to fill them.
  94     if (newStyle->width().isSpecifiedOrIntrinsic() && newStyle->height().isSpecifiedOrIntrinsic()) {
  95         placeHolder->setInlineStyleProperty(CSSPropertyWidth, 100, CSSPrimitiveValue::UnitType::Percentage);
  96         placeHolder->setInlineStyleProperty(CSSPropertyHeight, 100, CSSPrimitiveValue::UnitType::Percentage);
  97     }
  98
  99     // Make sure the broken image icon appears on the appropriate side of the image for the element's writing direction.
 100     brokenImage->setInlineStyleProperty(CSSPropertyFloat, AtomicString(newStyle->direction() == LTR ? "left" : "right"));
 101
 102     // This is an <img> with no attributes, so don't display anything.
 103     if (noImageSourceSpecified(element) && !newStyle->width().isSpecifiedOrIntrinsic() && !newStyle->height().isSpecifiedOrIntrinsic() && toHTMLElement(element).altText().isEmpty())
 104         newStyle->setDisplay(NONE);
 105
 106     // This preserves legacy behaviour originally defined when alt-text was managed by LayoutImage.
 107     if (noImageSourceSpecified(element))
 108         brokenImage->setInlineStyleProperty(CSSPropertyDisplay, CSSValueNone);
 109     else
 110         brokenImage->setInlineStyleProperty(CSSPropertyDisplay, CSSValueInline);
 111
 112     return newStyle;
 113 }
 114
 115 } // namespace blink