void RenderSVGResourceMarker::calcViewport()
{
    if (!selfNeedsLayout())
        return;

    SVGMarkerElement* marker = toSVGMarkerElement(element());
    ASSERT(marker);

    SVGLengthContext lengthContext(marker);
    float w = marker->markerWidthCurrentValue().value(lengthContext);
    float h = marker->markerHeightCurrentValue().value(lengthContext);
    m_viewport = FloatRect(0, 0, w, h);
}