QT怎么实现圆形按钮

QT如何实现圆形按钮?
请看这张图片: http://hi.csdn.net/attachment/201006/28/2702037_1277732191x7A4.png  
是方形的一张图,但里面的蓝色区域是圆形的........

我想把我的程序中的按钮的icon设成这张图片,以实现windows自带的播放器Media player里的播放按钮那样的效果.......请教各位大侠怎样实现?

[解决办法]

C/C++ code

 class Button : public QGraphicsWidget {     Q_OBJECT public:     Button(const QPixmap &pixmap, QGraphicsItem *parent = 0)         : QGraphicsWidget(parent), _pix(pixmap)     {         setAcceptHoverEvents(true);         setCacheMode(DeviceCoordinateCache);     }     QRectF boundingRect() const     {         return QRectF(-65, -65, 130, 130);     }     QPainterPath shape() const     {         QPainterPath path;         path.addEllipse(boundingRect());         return path;     }     void paint(QPainter *painter, const QStyleOptionGraphicsItem *option, QWidget *)     {         bool down = option->state & QStyle::State_Sunken;         QRectF r = boundingRect();         QLinearGradient grad(r.topLeft(), r.bottomRight());         grad.setColorAt(down ? 1 : 0, option->state & QStyle::State_MouseOver ? Qt::white : Qt::lightGray);         grad.setColorAt(down ? 0 : 1, Qt::darkGray);         painter->setPen(Qt::darkGray);         painter->setBrush(grad);         painter->drawEllipse(r);         QLinearGradient grad2(r.topLeft(), r.bottomRight());         grad.setColorAt(down ? 1 : 0, Qt::darkGray);         grad.setColorAt(down ? 0 : 1, Qt::lightGray);         painter->setPen(Qt::NoPen);         painter->setBrush(grad);         if (down)             painter->translate(2, 2);         painter->drawEllipse(r.adjusted(5, 5, -5, -5));         painter->drawPixmap(-_pix.width()/2, -_pix.height()/2, _pix);     } signals:     void pressed(); protected:     void mousePressEvent(QGraphicsSceneMouseEvent *)     {         emit pressed();         update();     }     void mouseReleaseEvent(QGraphicsSceneMouseEvent *)     {         update();     } private:     QPixmap _pix; };
[解决办法]
C/C++ code
QPushButton *playButton = new QPushButton;playButton->setIcon(QIcon(...));
[解决办法]
一种方式像2楼一样， 另一种方式采用遮罩也行`··
C/C++ code
...QPixmap pixmap;QPushButton* pushButton = new QPushButton;pushButton->setIcon(pixmap);pushButton->setMask(pixMap.createHeuristicMask());...