Create Transparent PNG Image

I want to convert SVG to PNG without background (transparent)
I use QtWebKit to acquire this

But it's not work, are you give me some idea to fix it ?

svg2png.h

Code:

#ifndef WEBKIT_SVG_RENDERER
#define WEBKIT_SVG_RENDERER
 
#include <QWebView>
 
class WebKitSVGRenderer : public QWebView
{
    Q_OBJECT
 
public:
    QString fileName;
    QSize targetSize;
    WebKitSVGRenderer(QWidget *parent = 0);
 
private slots:
    void saveResult(bool ok);
};
 
#endif // WEBKIT_SVG_RENDERER

svg2png.cpp

Code:

#include "svg2png.h"
 
#include <iostream>
 
#include <QtGui>
#include <QtWebKit>
 
// large enough to enclose the SVG icons
#define MAGIC_SIZE 4095
 
WebKitSVGRenderer::WebKitSVGRenderer(QWidget *parent) : QWebView(parent)
{
    connect(this, SIGNAL(loadFinished(bool)), this, SLOT(saveResult(bool)));
    setFixedSize(MAGIC_SIZE, MAGIC_SIZE);
 
    QPalette pal = palette();
    pal.setColor(QPalette::Background, Qt::transparent);
    setPalette(pal);
}
 
#define EVAL_JS(x) page()->mainFrame()->evaluateJavaScript((x))
 
void WebKitSVGRenderer::saveResult(bool ok)
{
    // crude error-checking
    if (!ok) {
        std::cerr << "Failed loading " << qPrintable(url().toString()) << std::endl;
        QApplication::instance()->exit(1);
        return;
    }
 
    // ensure it is an SVG
    QString root = EVAL_JS("document.rootElement.nodeName").toString();
    if (root.isEmpty() || root.compare("svg", Qt::CaseInsensitive)) {
        std::cerr << "Not an SVG! " << qPrintable(url().toString()) << std::endl;
        close();
        return;
    }
 
    // get the dimension, i.e. the width and height attributes
    // Note: if an attribute is not defined WebKit would return the view's dimension
    // hence the hack of checking for the MAGIC_SIZE
    double ww = EVAL_JS("document.rootElement.width.baseVal.value").toDouble();
    double hh = EVAL_JS("document.rootElement.height.baseVal.value").toDouble();
    if (ww == 0.0 || hh == 0.0 || ww == MAGIC_SIZE || hh == MAGIC_SIZE) {
        std::cerr << "SVG does not specify proper width and height! " << std::endl;
        close();
        return;
    }
 
    // try to give the best output file
    if (fileName.isEmpty()) {
        fileName = QFileInfo(url().path()).completeBaseName();
        if (fileName.isEmpty())
            fileName = "result";
        fileName += ".png";
    }
 
    // create the target surface
    QSize t = targetSize.isValid() ? targetSize : QSize(ww, hh);
    QImage img(t, QImage::Format_ARGB32_Premultiplied);
    img.fill(Qt::transparent);
 
    // prepare the painter
    QPainter p(&img);
    qreal xs = targetSize.isValid() ? targetSize.width() / ww : 1.0;
    qreal ys = targetSize.isValid() ? targetSize.height() / hh : 1.0;
    p.scale(xs, ys);
 
    // the best quality
    p.setRenderHint(QPainter::Antialiasing);
    p.setRenderHint(QPainter::TextAntialiasing);
    p.setRenderHint(QPainter::SmoothPixmapTransform);
 
    page()->mainFrame()->render(&p);
    p.end();
 
    if (img.save(fileName, "png"))
        std::cout << "Result saved to " << qPrintable(fileName) << std::endl;
    else
        std::cout << "Failed to save to " << qPrintable(fileName) << std::endl;
 
    close();
}
 
static void usage()
{
    std::cout << "Rasterize an SVG icon to a PNG image" << std::endl << std::endl;
    std::cout << "  svg2png  input.svg [output.png [width height]]" << std::endl << std::endl;
    std::cout << "Examples: " << std::endl;
    std::cout << "  svg2png tiger.svg" << std::endl;
    std::cout << "  svg2png icon.svg icon.png 256 256" << std::endl;
    std::cout << std::endl;
}
 
int main(int argc, char * argv[])
{
    if ((argc < 2) || (argc == 4)) {
        usage();
        return 0;
    }
 
    QApplication a(argc, argv);
 
    WebKitSVGRenderer renderer;
    if (argc < 3)
        renderer.fileName = QString::fromLatin1(argv[2]);
    if (argc == 5) {
        int w = QString::fromLatin1(argv[3]).toInt();
        int h = QString::fromLatin1(argv[4]).toInt();
        renderer.targetSize = QSize(w, h);
        if (!renderer.targetSize.isValid() || w <= 0 || h <= 0) {
            std::cerr << "Please specify a valid target size !" << std::endl;
            return 0;
        }
    }
 
    QString str = QFileInfo(QString::fromLatin1(argv[1])).absoluteFilePath();
    renderer.load(QUrl::fromLocalFile(str));
 
    return a.exec();
}