Why the background is not transparent?

[SkripT]

Hi, I use the following code to obtain a window with the shape of the pixmap "tux.png". The problem is that the background is painted in black color. Where's the mistake? Thanks.

#include <QtGui>
 
int main( int argc, char **argv )
{
    QApplication a( argc, argv );
 
    QPixmap p("../tux.png");
    if (p.mask().isNull())
    {
	QImage img("../tux.png");
	if ( img.hasAlphaChannel() ) 
	    p.setMask(QBitmap::fromImage(img.createAlphaMask()));
	 else
	    p.setMask( QBitmap::fromImage(img.createHeuristicMask()));
    }
    QWidget w(0, Qt::FramelessWindowHint);
    QPalette palette = w.palette();
	palette.setBrush(QPalette::Window, QBrush(p));
	w.setPalette(palette);
    w.setFixedSize(p.size() );
     w.setMask(p.mask());
    w.show();
 
    return a.exec();
}

#include <QtGui>

int main( int argc, char **argv )
{
    QApplication a( argc, argv );

    QPixmap p("../tux.png");
    if (p.mask().isNull())
    {
	QImage img("../tux.png");
	if ( img.hasAlphaChannel() ) 
	    p.setMask(QBitmap::fromImage(img.createAlphaMask()));
	 else
	    p.setMask( QBitmap::fromImage(img.createHeuristicMask()));
    }
    QWidget w(0, Qt::FramelessWindowHint);
    QPalette palette = w.palette();
	palette.setBrush(QPalette::Window, QBrush(p));
	w.setPalette(palette);
    w.setFixedSize(p.size() );
     w.setMask(p.mask());
    w.show();
    
    return a.exec();
}

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