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Thread: Qwt Plot Picker as position indicator

  1. #1
    Join Date
    Aug 2012
    Qt products

    Default Qwt Plot Picker as position indicator

    Hi everyone!
    I use qwt plot in my project showing audio waveform. I need a qwt plot picker now to represent the current playback position. But I dont know how to set the value of a picker because AFAIK it responds to mouse movement or selecting polygons and stuff. All I want is a vertical line representing the current playback position but the QwtPlotMarker is not good for this because it uses replot() and in bigger files there are too many replots. QwtPlotPicker doesnt use replot I think. So this is maybe the solution but I can't find any code to set the picker's value manually and the bode example shows only the mouse movement tracking but I dont need it at all. I want a vertical line on my plot which doesnt use replot!!! please help me! Thanks in advance!

  2. #2
    Join Date
    Feb 2006
    Munich, Germany
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    Default Re: Qwt Plot Picker as position indicator

    In one of the Qwt support channels I posted once a complete implementation of such a thing ( basically it was a picker with a QwtPickerTrackerMachine, where the append and move calls were set manually instead of being triggered by user input ). Of course this is a hack - but check the archives.

    Today I would recommend to use QwtPlotOverlay from SVN trunk ( copy it to your code when you want to use Qwt 6.0 ):
    Qt Code:
    1. class YourIndicator: public QwtPlotOverlay
    2. {
    3. public:
    4. void setPosition( double x )
    5. {
    6. m_position = x;
    7. updateOverlay();
    8. }
    10. virtual void drawOverlay( QPainter *painter ) const
    11. {
    12. const QwtPlot *plot = dynamic_cast<const QwtPlot *>( parent()->parent() );
    13. const double x = plot->canvasMap( QwtPlot::xBottom ).transform( m_position );
    15. painter->setPen( ... );
    16. painter->drawLine( x, 0, x, height() );
    17. }
    19. private:
    20. double m_position;
    21. }
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    When it is time I will add something like above to the examples.


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