小問題~~~~關於畫圓

[bibisamdi]

QCanvasPolygonalItem* i = new QCanvasEllipse (50,50,&canvas);

i->setBrush( QColor(rand()%32*8,rand()%32*8,rand()% 32*8) );

i->move(rand()%canvas.width(),rand()%canvas.height());
i->setZ(rand()%256);
i->show();

我用上面的程式碼來畫圓 可是我想畫空心的圓~~~~畫在canvas上

請問一下 應該要怎麼畫 才能畫出空心的~~~~謝謝