下面是The Scribe Classes 中举例用的一段代码,大家可以亲自到Qt Assistant里面去看：
QTextLayout textLayout(text, font);
qreal margin = 10;
qreal radius = qMin(width()/2.0, height()/2.0) - margin;
QFontMetrics fm(font);
qreal lineHeight = fm.height();
qreal y = 0;
textLayout.beginLayout();
while (1) {
// create a new line
QTextLine line = textLayout.createLine();
if (!line.isValid())
break;
qreal x1 = qMax(0.0, pow(pow(radius,2)-pow(radius-y,2), 0.5));
qreal x2 = qMax(0.0, pow(pow(radius,2)-pow(radius-(y+lineHeight),2), 0.5));
qreal x = qMax(x1, x2) + margin;
qreal lineWidth = (width() - margin) - x;
line.setLineWidth(lineWidth);
line.setPosition(QPointF(x, margin+y));
y += line.height();
}
textLayout.endLayout();
QPainter painter;
painter.begin(this);
painter.setRenderHint(QPainter::Antialiasing);
painter.fillRect(rect(), Qt::white);
painter.setBrush(QBrush(Qt::black));
painter.setPen(QPen(Qt::black));
textLayout.draw(&painter, QPoint(0,0));
painter.setBrush(QBrush(QColor("#a6ce39")));
painter.setPen(QPen(Qt::black));
painter.drawEllipse(QRectF(-radius, margin, 2*radius, 2*radius));
painter.end();
我的问题是：上面红色标记的两行用的pow()这个函数在Qt Assistant里面找不到，这是为什么？
如果，他不是系统提供的函数，又为何不说明其作用是什么？我花了大半天都不知道，他到底要表现什么用意？？？？？？？？？？？？？？？？？？？？？？？？？？？？？？
