Qt绘图控件qwt绘制等比例坐标图

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();
}
}