Generate SVG with viewBox attribute

[Aaron Weber]

I'm trying to render a PDF page (from PDFBox) to SVG image, and in order to
assist with browsers auto-scaling the resultant image, I find that the
viewBox attribute should be set in the svg (root) element.  Currently using
Java 8 and Batik 1.16.

I have looked at an old question in the list about this, but the mail
archive seems incomplete and what I've tried from it does not work.  If I
try to add the attribute before rendering the page via SVGGraphics2D, it
simply does not appear in the resultant output.  If I try to add it after
rendering the page, it actually ALSO does not appear, and my content of the
element is also gone.

FWIW: I think this would be a great method to add to SVGGeneratorContext.

My code is as follows.  Can someone point out how to edit the XML/SVG such
that the viewBox attribute is included successfully in the output?

            PDFRenderer r = new PDFRenderer(document);

            PDPage page = document.getPage(PageNumber - 1);
            PDRectangle rect = page.getMediaBox();
            int w = Math.round(rect.getWidth());
            int h = Math.round(rect.getHeight());
            String viewboxInfo = String.format("0 0 %d %d", w, h);

            String svgNS = "http://www.w3.org/2000/svg";;
            DOMImplementation impl =
GenericDOMImplementation.getDOMImplementation();
            Document myFactory = impl.createDocument(svgNS, "svg", null);

            SVGGeneratorContext ctx =
SVGGeneratorContext.createDefault(myFactory);
            ctx.setEmbeddedFontsOn(true);
            SVGGraphics2D g2d = new SVGGraphics2D(ctx, true);

            r.renderPageToGraphics(PageNumber - 1, g2d);

            Element root = g2d.getRoot();
            root.setAttribute("viewBox", viewboxInfo);

            try (Writer out = new
OutputStreamWriter(Files.newOutputStream(new File(tgtFilePath).toPath()),
"UTF-8"))
            {
                g2d.stream(out, true);
            }

Thanks.
-AJ