摘要：
在找到这个类之前，我有一个手动编写方法。其原理是将QwtPlotZoomer的缩放信号与QwtPlot类中写入的插槽连接起来，并重写QwtPlot类中的resizeEvent事件：void TrackPlot:：zoomedSlot｛QPointFcenterPoint=rectF.center（）；doubleRatio=rectF.width（）/rectF.height（）；doublehvRatio=double/double；如果｛doublescaleFactor=hvRatio/atio＞1？
需要用到QwtPlotRescaler类，用法如下：
QwtPlotRescaler *plotRescaler = new QwtPlotRescaler(canvas, yLeft, QwtPlotRescaler::Fitting ); plotRescaler->setExpandingDirection(QwtPlotRescaler::ExpandBoth);
其构造函数可以设置参考坐标轴，及其缩放动作，默认其他轴与参考轴的比例为1.0。setExpandingDirection函数可以指定在固定好参考轴后，另一轴拉伸时的模式，QwtPlotRescaler::ExpandBoth参数是指向两边扩展。
在找到这个类前，我有一个手动写法，原理是将QwtPlotZoomer的zoomed(const QRectF &)信号与在它所在的QwtPlot类中编写的槽相连，并重写QwtPlot类中的resizeEvent事件：
void TrackPlot::zoomedSlot(const QRectF &rectF) { QPointF centerPoint = rectF.center(); double Ratio = rectF.width() / rectF.height(); double hvRatio = double(canvas()->width()) / double(canvas()->height()); if(Ratio > 1) { double scaleFactor = hvRatio / Ratio > 1 ? hvRatio / Ratio : 1; setAxisScale(xBottom, centerPoint.x() - scaleFactor * rectF.width() / 2.0, centerPoint.x() + scaleFactor * rectF.width() / 2.0); double step = axisStepSize(xBottom); setAxisScale(yLeft, centerPoint.y() - scaleFactor * rectF.width() / (2.0 * hvRatio), scaleFactor * centerPoint.y() + scaleFactor * rectF.width() / (2.0 * hvRatio), step); } else { double scaleFactor = Ratio / hvRatio > 1 ? Ratio / hvRatio : 1; setAxisScale(yLeft, centerPoint.y() - scaleFactor * rectF.height() / 2.0, centerPoint.y() + scaleFactor * rectF.height() / 2.0); double step = axisStepSize(yLeft); setAxisScale(xBottom, centerPoint.x() - scaleFactor * rectF.height() * hvRatio / 2.0, centerPoint.x() + scaleFactor * rectF.height() * hvRatio / 2.0, step); } replot(); } void TrackPlot::resizeEvent(QResizeEvent *ev) { QwtPlot::resizeEvent(ev); if(ev->oldSize().width() > 5) { double hRatio = double(ev->size().width()) / double(ev->oldSize().width()); double vRatio = double(ev->size().height()) / double(ev->oldSize().height()); if(hRatio != 1) printf(""); double xLowBound = axisScaleDiv(xBottom).lowerBound(); double xUpperBound = axisScaleDiv(xBottom).upperBound(); double yLowBound = axisScaleDiv(yLeft).lowerBound(); double yUpperBound = axisScaleDiv(yLeft).upperBound(); setAxisScale(xBottom, hRatio * xLowBound, hRatio * xUpperBound); double ystep = axisStepSize(xBottom); setAxisScale(yLeft, vRatio * yLowBound, vRatio * yUpperBound, ystep); replot(); } else { double minX = axisScaleDiv(xBottom).lowerBound(); double maxX = axisScaleDiv(xBottom).upperBound(); double minY = axisScaleDiv(yLeft).lowerBound(); double maxY = axisScaleDiv(yLeft).upperBound(); QRectF rectF = QRectF(minX, minY, maxX - minX, maxY - minY); QPointF centerPoint = rectF.center(); double Ratio = rectF.width() / rectF.height(); double hvRatio = double(canvas()->width()) / double(canvas()->height()); if(Ratio > 1) { double scaleFactor = hvRatio / Ratio > 1 ? hvRatio / Ratio : 1; setAxisScale(xBottom, centerPoint.x() - scaleFactor * rectF.width() / 2.0, centerPoint.x() + scaleFactor * rectF.width() / 2.0); double step = axisStepSize(xBottom); setAxisScale(yLeft, centerPoint.y() - scaleFactor * rectF.width() / (2.0 * hvRatio), scaleFactor * centerPoint.y() + scaleFactor * rectF.width() / (2.0 * hvRatio), step); } else { double scaleFactor = Ratio / hvRatio > 1 ? Ratio / hvRatio : 1; setAxisScale(yLeft, centerPoint.y() - scaleFactor * rectF.height() / 2.0, centerPoint.y() + scaleFactor * rectF.height() / 2.0); double step = axisStepSize(yLeft); setAxisScale(xBottom, centerPoint.x() - scaleFactor * rectF.height() * hvRatio / 2.0, centerPoint.x() + scaleFactor * rectF.height() * hvRatio / 2.0, step); } replot(); } }