I need to make a plot with a fixed aspect ratio. It seems that QwtPlotRescaler is intended for this too, but I cannot make it work at all. I made a very simple example:
Qt Code: 
  1. MainWindow::MainWindow(QWidget *parent) :
  2.     QMainWindow(parent),
  3.     ui(new Ui::MainWindow)
  4. {
  5.     ui->setupUi(this);
  6.     this->setLayout(new QVBoxLayout(this));
  7.     QwtPlot *plot = new QwtPlot(this);
  8.  
  9.     QwtPlotCurve *curve = new QwtPlotCurve();
  10.     QPolygonF points;
  11.     points.append(QPointF(0, 0));
  12.     points.append(QPointF(1, 1));
  13.     curve->setSamples(points);
  14.     curve->attach(plot);
  15.  
  16.     // QwtPlotRescaler section start
  17.     QwtPlotRescaler *rescaler = new QwtPlotRescaler(plot->canvas());
  18.     rescaler->setReferenceAxis(QwtPlot::xBottom);
  19.     rescaler->setAspectRatio(QwtPlot::yLeft, 1.0);
  20.     rescaler->setRescalePolicy(QwtPlotRescaler::Expanding);
  21.     rescaler->setEnabled(true);
  22.     rescaler->rescale();
  23.     plot->plotLayout()->setAlignCanvasToScales(true);
  24.    // QwtPlotRescaler section end
  25.  
  26.     this->setCentralWidget(plot);
  27. }
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Without QwtPlotRescaler section I get what I expect: a simple plot with a single straight line going from (0, 0) to (1, 1) and two axes, both from 0 to 1. After adding QwtPlotRescaler section I get an empty plot - no line, no axes, no ticks.