void SVGUseElement::buildShadowAndInstanceTree(SVGShadowTreeRootElement* shadowRoot) { struct ShadowTreeUpdateBlocker { ShadowTreeUpdateBlocker(SVGUseElement* currentUseElement) : useElement(currentUseElement) { useElement->setUpdatesBlocked(true); } ~ShadowTreeUpdateBlocker() { useElement->setUpdatesBlocked(false); } SVGUseElement* useElement; }; // When cloning the target nodes, they may decide to synchronize style and/or animated SVG attributes. // That causes calls to SVGElementInstance::updateAllInstancesOfElement(), which mark the shadow tree for recreation. // Solution: block any updates to the shadow tree while we're building it. ShadowTreeUpdateBlocker blocker(this); String id = SVGURIReference::getTarget(href()); Element* targetElement = document()->getElementById(id); if (!targetElement) { // The only time we should get here is when the use element has not been // given a resource to target. ASSERT(m_resourceId.isEmpty()); return; } // Do not build the shadow/instance tree for <use> elements living in a shadow tree. // The will be expanded soon anyway - see expandUseElementsInShadowTree(). ContainerNode* parent = parentNode(); while (parent) { if (parent->isShadowRoot()) return; parent = parent->parentNodeGuaranteedHostFree(); } SVGElement* target = 0; if (targetElement && targetElement->isSVGElement()) target = static_cast<SVGElement*>(targetElement); detachInstance(); // Do not allow self-referencing. // 'target' may be null, if it's a non SVG namespaced element. if (!target || target == this) return; // Why a seperated instance/shadow tree? SVG demands it: // The instance tree is accesable from JavaScript, and has to // expose a 1:1 copy of the referenced tree, whereas internally we need // to alter the tree for correct "use-on-symbol", "use-on-svg" support. // Build instance tree. Create root SVGElementInstance object for the first sub-tree node. // // Spec: If the 'use' element references a simple graphics element such as a 'rect', then there is only a // single SVGElementInstance object, and the correspondingElement attribute on this SVGElementInstance object // is the SVGRectElement that corresponds to the referenced 'rect' element. m_targetElementInstance = SVGElementInstance::create(this, target); // Eventually enter recursion to build SVGElementInstance objects for the sub-tree children bool foundProblem = false; buildInstanceTree(target, m_targetElementInstance.get(), foundProblem); // SVG specification does not say a word about <use> & cycles. My view on this is: just ignore it! // Non-appearing <use> content is easier to debug, then half-appearing content. if (foundProblem) { detachInstance(); return; } // Assure instance tree building was successfull ASSERT(m_targetElementInstance); ASSERT(!m_targetElementInstance->shadowTreeElement()); ASSERT(m_targetElementInstance->correspondingUseElement() == this); ASSERT(m_targetElementInstance->correspondingElement() == target); // Build shadow tree from instance tree // This also handles the special cases: <use> on <symbol>, <use> on <svg>. buildShadowTree(shadowRoot, target, m_targetElementInstance.get()); #if ENABLE(SVG) && ENABLE(SVG_USE) // Expand all <use> elements in the shadow tree. // Expand means: replace the actual <use> element by what it references. expandUseElementsInShadowTree(shadowRoot, shadowRoot); // Expand all <symbol> elements in the shadow tree. // Expand means: replace the actual <symbol> element by the <svg> element. expandSymbolElementsInShadowTree(shadowRoot, shadowRoot); #endif // Now that the shadow tree is completly expanded, we can associate // shadow tree elements <-> instances in the instance tree. associateInstancesWithShadowTreeElements(shadowRoot->firstChild(), m_targetElementInstance.get()); // If no shadow tree element is present, this means that the reference root // element was removed, as it is disallowed (ie. <use> on <foreignObject>) // Do NOT leave an inconsistent instance tree around, instead destruct it. if (!m_targetElementInstance->shadowTreeElement()) { shadowRoot->removeAllChildren(); detachInstance(); return; } // Consistency checks - this is assumed in updateContainerOffset(). ASSERT(m_targetElementInstance->shadowTreeElement()->parentNode() == shadowRoot); // Eventually dump instance tree #ifdef DUMP_INSTANCE_TREE String text; unsigned int depth = 0; dumpInstanceTree(depth, text, m_targetElementInstance.get()); fprintf(stderr, "\nDumping <use> instance tree:\n%s\n", text.latin1().data()); #endif // Eventually dump shadow tree #ifdef DUMP_SHADOW_TREE ExceptionCode ec = 0; RefPtr<XMLSerializer> serializer = XMLSerializer::create(); String markup = serializer->serializeToString(shadowRoot, ec); ASSERT(!ec); fprintf(stderr, "Dumping <use> shadow tree markup:\n%s\n", markup.latin1().data()); #endif // Transfer event listeners assigned to the referenced element to our shadow tree elements. transferEventListenersToShadowTree(m_targetElementInstance.get()); // Update container offset/size updateContainerOffsets(); updateContainerSizes(); // Update relative length information updateRelativeLengthsInformation(); }