how to get axis range when autoscale is on?

[hind]

Are you reinventing a QwtPlotMarker::HLine marker ?

Uwe

Sorry but I didn't think I need a QwtPlotMarker::HLine marker because the regression line I was drawing could have any slope. I checked the doc of QwtPlotMarker again but found no useful info on this. Tell me if I missed something. Thanks again!

Are you reinventing a QwtPlotMarker::HLine marker ?

Uwe

Sorry but I didn't think I need a QwtPlotMarker::HLine marker because the regression line I was drawing could have any slope. I checked the doc of QwtPlotMarker again but found no useful info on this. Tell me if I missed something. Thanks again!

[Uwe]

Well, how is your regression line defined: y = m * x + t ?

For such a thing I would implement my own plot item. In its draw method you know the geometry of the canvas and using QLineF you can easily calculate the cutting points of the line with the canvas borders.
The rescaler example shows a plot item that draws a rectangle ( only an example, with QwtPlotShapeItem this could be done as well ). Your plot item will - of course - be different, but not more difficult.

Uwe