QPainter创建路径
路径的交叉并补可以通过函数或者操作符进行操作，如下：
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//函数
QPainterPath subtracted(const QPainterPath &p) const; //差集
QPainterPath united(const QPainterPath &p) const; //并集
QPainterPath intersected(const QPainterPath &p) const;//交集
//操作符
QPainterPath operator&(const QPainterPath &other) const;
QPainterPath &operator&=(const QPainterPath &other);
QPainterPath operator+(const QPainterPath &other) const;
QPainterPath &operator+=(const QPainterPath &other);
QPainterPath operator-(const QPainterPath &other) const;
QPainterPath &operator-=(const QPainterPath &other);
示例代码：
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void QwIFNTProgressBar::Pate_Test3(QPainter& painter)
{
painter.save();
painter.setWindow(0, 0, 400, 400);
painter.translate(200,0);
painter.scale(0.8, 0.8);
painter.setRenderHint(QPainter::Antialiasing);
QPainterPath path;
path.lineTo(100, 0);
path.cubicTo(200, 0, 100, 50, 200, 100);
path.closeSubpath();
path.addRect(50, 50, 50, 50);
QPainterPath path2;
path2.addEllipse(80, 30, 50, 50);
path = path.subtracted(path2);
QPoint offsetPoint(20, 20);
painter.translate(offsetPoint);
painter.setBrush(Qt::lightGray);
painter.drawPath(path);
painter.setBrush(Qt::NoBrush);
painter.drawRect(path.boundingRect());
QPen pen;
pen.setWidth(5);
pen.setColor(Qt::red);
painter.setPen(pen);
painter.drawPoint(QPoint(100, 0) );
painter.drawPoint(QPoint(200, 0) );
painter.drawPoint(QPoint(100, 50) );
painter.drawPoint(QPoint(200, 100) );
painter.restore();
}
