How to get a fixed stepSize of AxisScale even after zooming

[beckjoh]

Hello,

I want to define a fixed step size for my x-scale (step=1). I can do this by using setAxisScale() method. But after zooming it's lost.
Here is my example code:

//create a plot
QwtPlot plot;
 
//create a curve
QwtPlotCurve curve = QwtPlotCurve();
double x[] = {0,1,2,3,4,5,6,7,8,9,10};
double y[] = {1,2,3,2,1,0,1,2,3,2,1};;
curve.setRawSamples(x, y, 11);
curve.attach(&plot);
 
//create zoom
QwtPlotMagnifier zoom = QwtPlotMagnifier(plot.canvas());
zoom.setAxisEnabled(QwtPlot::xBottom,true);
 
//set scale
plot.setAxisScale(QwtPlot::xBottom,0,10,1);
 
//show plot
plot.show();

//create a plot
QwtPlot plot;

//create a curve
QwtPlotCurve curve = QwtPlotCurve();
double x[] = {0,1,2,3,4,5,6,7,8,9,10};
double y[] = {1,2,3,2,1,0,1,2,3,2,1};;
curve.setRawSamples(x, y, 11);
curve.attach(&plot);

//create zoom
QwtPlotMagnifier zoom = QwtPlotMagnifier(plot.canvas());
zoom.setAxisEnabled(QwtPlot::xBottom,true);

//set scale
plot.setAxisScale(QwtPlot::xBottom,0,10,1);

//show plot
plot.show();

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What I want:
- fixed major ticks with a step=1, independant if I zoomed in or zoomed out

Is there an easy way to do that with just calling a method?
If not, how can I get around this the best way? Reimplementing ScaleEngine?

regards
Johannes

[Cah]

Do this....

connect(((QObject*)plot->axisWidget(QwtPlot::xBottom)) , SIGNAL(scaleDivChanged () ), this, SLOT(scaleDivChangedSlot () ));


implement the slot...

void scaleDivChangedSlot ()
{
//restore the scale to what ever you want
}

[Uwe]

Reimplementing ScaleEngine?

Yes - this is probably better, than calculating a scale you don't want first - fixing it later.

Simply overload QwtLinearScaleEngine::divideScale() - should be a couple of lines only.

Uwe

[beckjoh]

Thank you both for your answers!

First attempt i tried and it works, but I will try Uwe's solution too.

Johannes