ok 成功了
QImage imgback("c:/tmp.png");
QBrush qb(imgback);
QPainterPath path;
path.moveTo(10,100);
path.lineTo(200,50);
path.lineTo(220,80);
path.lineTo(200,110);
path.lineTo(200,90);
path.closeSubpath();
QImage img(300,300,QImage::Format_ARGB32);
QPainter g(&img);
g.setBrush(qb);
g.drawPath(path);
QPainter p(this);
p.drawImage(0,0,img);