C++ LayoutObject::canHaveChildren方法代码示例

bool Text::textLayoutObjectIsNeeded(const ComputedStyle& style, const LayoutObject& parent)
{
    if (!parent.canHaveChildren())
        return false;

    if (isEditingText())
        return true;

    if (!length())
        return false;

    if (style.display() == NONE)
        return false;

    if (!containsOnlyWhitespace())
        return true;

    if (!canHaveWhitespaceChildren(parent, this))
        return false;

    // pre-wrap in SVG never makes layoutObject.
    if (style.whiteSpace() == PRE_WRAP && parent.isSVG())
        return false;

    // pre/pre-wrap/-bb-pre-wrap-text/pre-line always make layoutObjects.
    if (style.preserveNewline())
        return true;

    // childNeedsDistributionRecalc() here is rare, only happens JS calling surroundContents() etc. from DOMNodeInsertedIntoDocument etc.
    if (document().childNeedsDistributionRecalc())
        return true;

    const LayoutObject* prev = LayoutTreeBuilderTraversal::previousSiblingLayoutObject(*this);
    if (prev && prev->isBR()) // <span><br/> <br/></span>
        return false;

    if (parent.isLayoutInline()) {
        // <span><div/> <div/></span>
        if (prev && !prev->isInline() && !prev->isOutOfFlowPositioned())
            return false;
    } else {
        if (parent.isLayoutBlock() && !parent.childrenInline() && (!prev || !prev->isInline()))
            return false;

        // Avoiding creation of a layoutObject for the text node is a non-essential memory optimization.
        // So to avoid blowing up on very wide DOMs, we limit the number of siblings to visit.
        unsigned maxSiblingsToVisit = 50;

        LayoutObject* first = parent.slowFirstChild();
        while (first && first->isFloatingOrOutOfFlowPositioned() && maxSiblingsToVisit--)
            first = first->nextSibling();
        if (!first || first == layoutObject() || LayoutTreeBuilderTraversal::nextSiblingLayoutObject(*this) == first) {
            // Whitespace at the start of a block just goes away.  Don't even
            // make a layout object for this text.
            return false;
        }
    }
    return true;
}

bool LayoutTreeBuilderForElement::shouldCreateLayoutObject() const
{
    if (!m_layoutObjectParent)
        return false;

    // FIXME: Should the following be in SVGElement::layoutObjectIsNeeded()?
    if (m_node->isSVGElement()) {
        // SVG elements only render when inside <svg>, or if the element is an <svg> itself.
        if (!isSVGSVGElement(*m_node) && (!m_layoutObjectParent->node() || !m_layoutObjectParent->node()->isSVGElement()))
            return false;
        if (!toSVGElement(m_node)->isValid())
            return false;
    }

    LayoutObject* parentLayoutObject = this->parentLayoutObject();
    if (!parentLayoutObject)
        return false;
    if (!parentLayoutObject->canHaveChildren())
        return false;

    return m_node->layoutObjectIsNeeded(style());
}