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

// Copyright 2014 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#include "core/html/HTMLImageFallbackHelper.h"

#include "core/HTMLNames.h"
#include "core/InputTypeNames.h"
#include "core/dom/ElementRareData.h"
#include "core/dom/Text.h"
#include "core/dom/shadow/ShadowRoot.h"
#include "core/html/HTMLDivElement.h"
#include "core/html/HTMLElement.h"
#include "core/html/HTMLImageElement.h"
#include "core/html/HTMLImageLoader.h"
#include "core/html/HTMLInputElement.h"
#include "core/html/HTMLStyleElement.h"
#include "wtf/text/StringBuilder.h"

namespace blink {

using namespace HTMLNames;

static bool noImageSourceSpecified(const Element& element) {
  bool noSrcSpecified = !element.hasAttribute(srcAttr) ||
                        element.getAttribute(srcAttr).isNull() ||
                        element.getAttribute(srcAttr).isEmpty();
  bool noSrcsetSpecified = !element.hasAttribute(srcsetAttr) ||
                           element.getAttribute(srcsetAttr).isNull() ||
                           element.getAttribute(srcsetAttr).isEmpty();
  return noSrcSpecified && noSrcsetSpecified;
}

void HTMLImageFallbackHelper::createAltTextShadowTree(Element& element) {
  ShadowRoot& root = element.ensureUserAgentShadowRoot();

  HTMLDivElement* container = HTMLDivElement::create(element.document());
  root.appendChild(container);
  container->setAttribute(idAttr, AtomicString("alttext-container"));
  container->setInlineStyleProperty(CSSPropertyOverflow, CSSValueHidden);
  container->setInlineStyleProperty(CSSPropertyBorderWidth, 1,
                                    CSSPrimitiveValue::UnitType::Pixels);
  container->setInlineStyleProperty(CSSPropertyBorderStyle, CSSValueSolid);
  container->setInlineStyleProperty(CSSPropertyBorderColor, CSSValueSilver);
  container->setInlineStyleProperty(CSSPropertyDisplay, CSSValueInlineBlock);
  container->setInlineStyleProperty(CSSPropertyBoxSizing, CSSValueBorderBox);
  container->setInlineStyleProperty(CSSPropertyPadding, 1,
                                    CSSPrimitiveValue::UnitType::Pixels);

  HTMLImageElement* brokenImage = HTMLImageElement::create(element.document());
  container->appendChild(brokenImage);
  brokenImage->setIsFallbackImage();
  brokenImage->setAttribute(idAttr, AtomicString("alttext-image"));
  brokenImage->setAttribute(widthAttr, AtomicString("16"));
  brokenImage->setAttribute(heightAttr, AtomicString("16"));
  brokenImage->setAttribute(alignAttr, AtomicString("left"));
  brokenImage->setInlineStyleProperty(CSSPropertyMargin, 0,
                                      CSSPrimitiveValue::UnitType::Pixels);

  HTMLDivElement* altText = HTMLDivElement::create(element.document());
  container->appendChild(altText);
  altText->setAttribute(idAttr, AtomicString("alttext"));
  altText->setInlineStyleProperty(CSSPropertyOverflow, CSSValueHidden);
  altText->setInlineStyleProperty(CSSPropertyDisplay, CSSValueBlock);

  Text* text =
      Text::create(element.document(), toHTMLElement(element).altText());
  altText->appendChild(text);
}

PassRefPtr<ComputedStyle> HTMLImageFallbackHelper::customStyleForAltText(
    Element& element,
    PassRefPtr<ComputedStyle> newStyle) {
  // If we have an author shadow root or have not created the UA shadow root
  // yet, bail early. We can't use ensureUserAgentShadowRoot() here because that
  // would alter the DOM tree during style recalc.
  if (element.authorShadowRoot() || !element.userAgentShadowRoot())
    return newStyle;

  Element* placeHolder =
      element.userAgentShadowRoot()->getElementById("alttext-container");
  Element* brokenImage =
      element.userAgentShadowRoot()->getElementById("alttext-image");
  // Input elements have a UA shadow root of their own. We may not have replaced
  // it with fallback content yet.
  if (!placeHolder || !brokenImage)
    return newStyle;

  if (element.document().inQuirksMode()) {
    // Mimic the behaviour of the image host by setting symmetric dimensions if
    // only one dimension is specified.
    if (newStyle->width().isSpecifiedOrIntrinsic() &&
        newStyle->height().isAuto())
      newStyle->setHeight(newStyle->width());
    else if (newStyle->height().isSpecifiedOrIntrinsic() &&
             newStyle->width().isAuto())
      newStyle->setWidth(newStyle->height());
    if (newStyle->width().isSpecifiedOrIntrinsic() &&
        newStyle->height().isSpecifiedOrIntrinsic()) {
      placeHolder->setInlineStyleProperty(CSSPropertyVerticalAlign,
                                          CSSValueBaseline);
    }
  }

  // If the image has specified dimensions allow the alt-text container expand
  // to fill them.
  if (newStyle->width().isSpecifiedOrIntrinsic() &&
      newStyle->height().isSpecifiedOrIntrinsic()) {
    placeHolder->setInlineStyleProperty(
        CSSPropertyWidth, 100, CSSPrimitiveValue::UnitType::Percentage);
    placeHolder->setInlineStyleProperty(
        CSSPropertyHeight, 100, CSSPrimitiveValue::UnitType::Percentage);
  }

  // Make sure the broken image icon appears on the appropriate side of the
  // image for the element's writing direction.
  brokenImage->setInlineStyleProperty(
      CSSPropertyFloat,
      AtomicString(newStyle->direction() == TextDirection::Ltr ? "left"
                                                               : "right"));

  // This is an <img> with no attributes, so don't display anything.
  if (noImageSourceSpecified(element) &&
      !newStyle->width().isSpecifiedOrIntrinsic() &&
      !newStyle->height().isSpecifiedOrIntrinsic() &&
      toHTMLElement(element).altText().isEmpty())
    newStyle->setDisplay(EDisplay::None);

  // This preserves legacy behaviour originally defined when alt-text was
  // managed by LayoutImage.
  if (noImageSourceSpecified(element))
    brokenImage->setInlineStyleProperty(CSSPropertyDisplay, CSSValueNone);
  else
    brokenImage->setInlineStyleProperty(CSSPropertyDisplay, CSSValueInline);

  return newStyle;
}

}  // namespace blink