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Thread: Refreshing a Custom QwtScaleDraw

  1. #1
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    Default Refreshing a Custom QwtScaleDraw

    Hi, I have reimplemented QwtScaleDraw.

    When I start plotting data I would like the current time to be displayed. Not the time when the application started.

    I reset my QTime, It does eventually display the right time after the plot starts to auto scale.

    Thanks in advance
    Brendan

    Qt Code:
    1. class TimeScaleDraw: public QwtScaleDraw
    2. {
    3. public:
    4. TimeScaleDraw();
    5. void start();
    6. virtual QwtText label(double) const;
    7.  
    8. private:
    9. QTime m_base_time;
    10. };
    11.  
    12. TimeScaleDraw::TimeScaleDraw()
    13. {
    14. start();
    15. }
    16.  
    17. QwtText TimeScaleDraw::label(double v) const
    18. {
    19. QTime upTime = m_base_time.addMSecs((int)v);
    20.  
    21. return upTime.toString("H:mm:ss.zzz");
    22. }
    23.  
    24. void TimeScaleDraw::start()
    25. {
    26. m_base_time.start();
    27. //TODO: DO SOMETHING HERE TO REFRESH QwtScaleDraw???
    28. }
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  2. #2
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    Default Re: Refreshing a Custom QwtScaleDraw

    QwtPlot::replot()

    Uwe

  3. #3
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    Default Re: Refreshing a Custom QwtScaleDraw

    I tried calling qwtPlot->replot() after start() was called, this didn't make any difference.

    I have also tried passing the QwtPlot pointer to the class and running replot() with that pointer. This didn't make any difference.

    When I added QwtPlot::replot() to the class it gave the following error:
    "cannot call member function 'virtual void QwtPlot::replot()' without object"
    I tried adding friend classes etc.

    I don't seem to have the same problem with my custom QwtPlotPicker.

    Please excuse my stupidity in advance

  4. #4
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    Default Re: Refreshing a Custom QwtScaleDraw

    Qt Code:
    1. TimeScaleDraw* scaleDraw = dynamic_cast<TimeScaleDraw*>( plot->axisScaleDraw( ... ) );
    2. scaleDraw->start();
    3. scaleDraw->invalidateCache();
    4. plot->replot();
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    HTH,
    Uwe

  5. The following user says thank you to Uwe for this useful post:

    grantbj74 (19th March 2012)

  6. #5
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    Default Re: Refreshing a Custom QwtScaleDraw

    The scaleDraw->invalidateCache() gives a protected error when compiling.

    If I put invalidateCache() inside a new function that changes appearance in TimeScaleDraw class: eg ms, sec, clock etc it changes straight away.

    However if invalidateCache() is put in the end of start() time still doesn't update until the plot starts moving etc. I guess this isn't too much of an issue.

    I just use the following for time atm:
    Qt Code:
    1. QwtText TimeScaleDraw::label(double /*v*/) const
    2. {
    3. return m_base_time.toString("H:mm:ss.zzz");
    4. }
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  7. #6
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    Default Re: Refreshing a Custom QwtScaleDraw

    The call to invalidateCache() won't cause a replot on its own, it is just a method to ensure that the labels are recalculated the next time there -is- a replot. So after you construct your TimeScaleDraw class, call replot() from where ever you are in the code.

  8. #7
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    Default Re: Refreshing a Custom QwtScaleDraw

    Yeah I was calling replot() last but made no difference.

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