Avoid using SVGElementInstance in calcViewport

Source/core/svg/SVGUseElement.cpp

Index: Source/core/svg/SVGUseElement.cpp
diff --git a/Source/core/svg/SVGUseElement.cpp b/Source/core/svg/SVGUseElement.cpp
index ecdea38ef69b5fd4692b2d62d0236f271d2b4403..a638624ce3a2bf97d5a18742170af593ee1952b9 100644
--- a/Source/core/svg/SVGUseElement.cpp
+++ b/Source/core/svg/SVGUseElement.cpp
@@ -400,6 +400,25 @@ void SVGUseElement::buildPendingResource()
     ASSERT(!m_needsShadowTreeRecreation);
 }
 
+inline void transferUseWidthAndHeightIfNeeded(const SVGUseElement& use, Element& element)

[pdr., 2014/04/29 04:30:59]

It may be better to put the relevant code from this function into
expandSymbolElementsInShadowTree and expandUseElementsInShadowTree instead of
breaking it into a function.

+{
+    if (isSVGSymbolElement(element)) {
+        // Spec (<use> on <symbol>): This generated 'svg' will always have explicit values for attributes width and height.
+        // If attributes width and/or height are provided on the 'use' element, then these attributes
+        // will be transferred to the generated 'svg'. If attributes width and/or height are not specified,
+        // the generated 'svg' element will use values of 100% for these attributes.
+        element.setAttribute(SVGNames::widthAttr, use.hasAttribute(SVGNames::widthAttr) ? use.getAttribute(SVGNames::widthAttr) : "100%");
+        element.setAttribute(SVGNames::heightAttr, use.hasAttribute(SVGNames::heightAttr) ? use.getAttribute(SVGNames::heightAttr) : "100%");
+    } else if (isSVGSVGElement(element)) {
+        // Spec (<use> on <svg>): If attributes width and/or height are provided on the 'use' element, then these
+        // values will override the corresponding attributes on the 'svg' in the generated tree.
+        if (use.hasAttribute(SVGNames::widthAttr))

[Erik Dahlström (inactive), 2014/04/29 13:01:02]

Will this work if the width/height attributes are animated with SMIL? In those
cases the transferred values should really be the animated (current) value.

Will this patch mean worse performance for svgs that modify (either in script or
by other means) the width/height on <use> a lot?

+            element.setAttribute(SVGNames::widthAttr, use.getAttribute(SVGNames::widthAttr));
+        if (use.hasAttribute(SVGNames::heightAttr))
+            element.setAttribute(SVGNames::heightAttr, use.getAttribute(SVGNames::heightAttr));
+    }
+}
+
 void SVGUseElement::buildShadowAndInstanceTree(SVGElement* target)
 {
     ASSERT(!m_targetElementInstance);
@@ -452,13 +471,14 @@ void SVGUseElement::buildShadowAndInstanceTree(SVGElement* target)
     ASSERT(shadowTreeRootElement);
 
     // Build shadow tree from instance tree
-    // This also handles the special cases: <use> on <symbol>, <use> on <svg>.
+    // This clones the element corresponding to the target element instance
     buildShadowTree(target, m_targetElementInstance.get());
 
     // Expand all <use> elements in the shadow tree.
     // Expand means: replace the actual <use> element by what it references.
     expandUseElementsInShadowTree(shadowTreeRootElement);
 
+    transferUseWidthAndHeightIfNeeded(*this, *toSVGElement(shadowTreeRootElement->firstChild()));
     // Expand all <symbol> elements in the shadow tree.
     // Expand means: replace the actual <symbol> element by the <svg> element.
     expandSymbolElementsInShadowTree(shadowTreeRootElement);
@@ -702,6 +722,8 @@ void SVGUseElement::expandUseElementsInShadowTree(Node* element)
         if (target && !isDisallowedElement(target)) {
             RefPtr<Element> newChild = target->cloneElementWithChildren();
             ASSERT(newChild->isSVGElement());
+            transferUseWidthAndHeightIfNeeded(*use, *newChild);

[pdr., 2014/04/29 04:30:59]

I think the use width/height code would go here.

+
             cloneParent->appendChild(newChild.release());
         }