Obtaining infos from magnified plot

[mastupristi]

I have QwtPlot and QwtPlotMagnifier. I can zoom only x axes. When I zoom in I can see only a portion of my curve. How can I obtain which portion of curve I see in the plot canvas? That is, xMin and xMax of the drowed portion?

thanks

[cnbp173]

IIRC you can use invTransform(int axisID, int pos) on the QwtPlot to return the double value of the x-axis for start and finish.

The plot goes from 1 to 1000 (int), so 1 will be xMin and 1000 will be xMax.

I'm sure Uwe will be along to confirm shortly!

Cheers

[mastupristi]

The plot goes from 1 to 1000 (int), so 1 will be xMin and 1000 will be xMax.

I tried with 1000 as xMax, but it seems that is incorrect...
I tried using QwtScaleMap::transform(), applied with different windows size, and it seems thax xMax and xMin are pixel positions.
So I don't think I can successfully use invTransform, because I don't know xMin and xMax.

thanks

[cnbp173]

The way I currently do it (although I'm a bit rusty) is to link the signal zoomed(const QwtDoubleRect &) to a function and then you can take the left() and right() of the resultant QwtDoubleRect to give the xMin and xMax.

Not sure if this signal exists for the QwtMagnifier.

[Uwe]

a) All navigation operations (zooming, panning) ... finally end in a call of QwtPlot::setAxisScale() changing the scales of the scale widgets. Whenever a scale widget gets a new scale it emits QwtScaleWidget::scaleDivChanged(). With plot->axisScaleDiv() you can get the current scale divisions with all ticks and the left/right borders.

b) With plot->canvas()->contentsRect() you find the area of the plot canvas in widget coordinates. With plot->canvasMap()->invTransform() you can translate it into plot coordinates.

Uwe