How to set QBrush half transparent ?

When QBrush uses setTexture(QPixmap &), how to set it transparent ?
I have tried this :

QPixmap pix("D:/1.png");
QBitmap mask= pix.createMaskFromColor(QColor(255,0,255),Qt::Mask InColor);
pix.setMask(mask);

it doesn't work.

Try setting QColor's alpha-channel: http://qt-project.org/doc/qt-4.8/qcolor.html#QColor-2

o , how ,exactly ?

QColor(255,0,255,128)