synchronize the X-axis of two plots

[eehmke]

I have two QwtPlot diagrams that are in a vertical layout. The X axes have the same scale. The Y-axes have different scales and the bottom diagram has a second Y-axis at the right side. This leads to the effect that the X positions are not aligned to each other, making it difficult to interpret the corresponding values. How can I make sure that all corresponding X positions are aligned?

[Spitfire]

Is your problem the second Y axis that makes the plot smaller thus disaligning the plots?
If yes, then you could use setContentsMargin() on the plot without extra Y axis and set the right margin to the axis widget width.
If no, then I didn't understood your problem.

[eehmke]

Is your problem the second Y axis that makes the plot smaller thus disaligning the plots?
If yes, then you could use setContentsMargin() on the plot without extra Y axis and set the right margin to the axis widget width.

Thanks, will try that.
It's not only that the first plot does not have a right Y axis. Also the left Y axes have different size because the scale is different (large numbers as major ticks). The contentmargin of the plots seems always to be (0, 0, 0, 0)

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Added after 20 minutes:

Ok it works when I put some experimental values into the content margin. Next step would be to calculate them from the font size used to draw the scale ticks. Thanks!

[Spitfire]

You can tackle different sizes of Y axis widget by setting minimum extent:

QwtScaleDraw* sd = plot->axisScaleDraw( QwtPlot::yLeft );
sd->setMinimumExtent( 50 ); // magic number
plot->setAxisScaleDraw( QwtPlot::yLeft, sd );

QwtScaleDraw* sd = plot->axisScaleDraw( QwtPlot::yLeft );
sd->setMinimumExtent( 50 ); // magic number
plot->setAxisScaleDraw( QwtPlot::yLeft, sd );

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this way the widget will be at least that wide. Using that you can ensure that width of the widget is the same across different plots.