How to set previous Zoom positions using Qwt

[seguprasad]

Hi All,

I am zooming the selected region of the plot using the QwtPlotZoomer.How can i set the previous zoomed position using QwtPlotZoomer.

Thanks,

[bhs-ittech]

From reading the QwtPlotZoomer Class Reference

I'd say you should use:

class abc 
{
...
QwtPlotZoomer *some_zoomer;
...
public:
void last_zoom(void) {
  if(0 == some_zoomer->zoomRectIndex()) return;
  some_zoomer->zoom(-1);
}
...
};

class abc 
{
...
QwtPlotZoomer *some_zoomer;
...
public:
void last_zoom(void) {
  if(0 == some_zoomer->zoomRectIndex()) return;
  some_zoomer->zoom(-1);
}
...
};

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hope this helps

for more info see http://qwt.sourceforge.net/ or
http://qwt.sourceforge.net/class_qwt_plot_zoomer.html

[seguprasad]

Thanks for your response...

That is working only for zooming,if i need to implement for panning.How can i set the previous panned position.

Thanks,

[Uwe]

You need to implement a navigation history, where you have all zoomer and panner operations. One solution is to forward the rectangles of your panner into the zoom stack. Something like this:

virtual void YourPanner::moveCanvas(int dx, int dy)
{
    QwtPlotPanner::moveCanvas(dx, dy);
 
    QStack<QwtDoubleRect> &zoomStack =
        const_cast< QStack<QwtDoubleRect> >zoomer->zoomStack();
    zoomStack.push(zoomer->scaleRect());
    zoomer->zoom(1);  
}

virtual void YourPanner::moveCanvas(int dx, int dy)
{
    QwtPlotPanner::moveCanvas(dx, dy);

    QStack<QwtDoubleRect> &zoomStack =
        const_cast< QStack<QwtDoubleRect> >zoomer->zoomStack();
    zoomStack.push(zoomer->scaleRect());
    zoomer->zoom(1);  
}

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Of course this is only a workaround for a design problem of Qwt, that should better organize the navigation history inside the plot widget.

Uwe