Hello,

i use in my QwtPlot a curve tracker like in the playground example "CurveTracker".

Qt Code: 
  1. #include "curvetracker.h"
  2. #include <qwt_picker_machine.h>
  3. #include <qwt_series_data.h>
  4. #include <qwt_plot.h>
  5. #include <qwt_plot_curve.h>
  6.  
  7. struct compareX
  8. {
  9.     inline bool operator()( const double x, const QPointF &pos ) const
  10.     {
  11.         return ( x < pos.x() );
  12.     }
  13. };
  14.  
  15. CurveTracker::CurveTracker( QWidget *canvas ):
  16.     QwtPlotPicker( canvas )
  17. {
  18.     setTrackerMode( QwtPlotPicker::ActiveOnly );
  19.     setRubberBand( VLineRubberBand );
  20.  
  21.     setStateMachine( new QwtPickerDragPointMachine() );
  22. }
  23.  
  24. QRect CurveTracker::trackerRect( const QFont &font ) const
  25. {
  26.     QRect r = QwtPlotPicker::trackerRect( font );
  27.  
  28.     // align r to the first curve
  29.  
  30.     const QwtPlotItemList curves = plot()->itemList( QwtPlotItem::Rtti_PlotCurve );
  31.     if ( curves.size() > 0 )
  32.     {
  33.         QPointF pos = invTransform( trackerPosition() );
  34.  
  35.         const QLineF line = curveLineAt(    
  36.             static_cast<const QwtPlotCurve *>( curves[0] ), pos.x() );
  37.         if ( !line.isNull() )
  38.         {
  39.             const double curveY = line.pointAt(
  40.                 ( pos.x() - line.p1().x() ) / line.dx() ).y();
  41.  
  42.             pos.setY( curveY );
  43.             pos = transform( pos );
  44.  
  45.             r.moveBottom( pos.y() );
  46.         }
  47.     }
  48.  
  49.     return r;
  50. }
  51.  
  52. QwtText CurveTracker::trackerTextF( const QPointF &pos ) const
  53. {
  54.     QwtText trackerText;
  55.  
  56.     trackerText.setColor( Qt::black );
  57.  
  58.     QColor c( "#333333" );
  59.     trackerText.setBorderPen( QPen( c, 2 ) );
  60.     c.setAlpha( 200 );
  61.     trackerText.setBackgroundBrush( c );
  62.  
  63.     QString info;
  64.  
  65.     const QwtPlotItemList curves = 
  66.         plot()->itemList( QwtPlotItem::Rtti_PlotCurve );
  67.  
  68.     for ( int i = 0; i < curves.size(); i++ )
  69.     {
  70.         const QString curveInfo = curveInfoAt( 
  71.             static_cast<const QwtPlotCurve *>( curves[i] ), pos );
  72.  
  73.         if ( !curveInfo.isEmpty() )
  74.         {
  75.             if ( !info.isEmpty() )
  76.                 info += "<br>";
  77.  
  78.             info += curveInfo;
  79.         }
  80.     }
  81.  
  82.     trackerText.setText( info );
  83.     return trackerText;
  84. }
  85.  
  86. QString CurveTracker::curveInfoAt( 
  87.     const QwtPlotCurve *curve, const QPointF &pos ) const
  88. {
  89.     const QLineF line = curveLineAt( curve, pos.x() );
  90.     if ( line.isNull() )
  91.         return QString::null;
  92.  
  93.     const double y = line.pointAt( 
  94.         ( pos.x() - line.p1().x() ) / line.dx() ).y();
  95.  
  96.     QString info( "<font color=""%1"">%2</font>" );
  97.     return info.arg( curve->pen().color().name() ).arg( y );
  98. }
  99.  
  100. QLineF CurveTracker::curveLineAt( 
  101.     const QwtPlotCurve *curve, double x ) const
  102. {
  103.     QLineF line;
  104.  
  105.     if ( curve->dataSize() >= 2 )
  106.     {
  107.         const QRectF br = curve->boundingRect();
  108.         if ( ( br.width() > 0 ) && ( x >= br.left() ) && ( x <= br.right() ) )
  109.         {
  110.             int index = qwtUpperSampleIndex<QPointF>( 
  111.                 *curve->data(), x, compareX() );
  112.  
  113.             if ( index == -1 && 
  114.                 x == curve->sample( curve->dataSize() - 1 ).x() )
  115.             {
  116.                 // the last sample is excluded from qwtUpperSampleIndex
  117.                 index = curve->dataSize() - 1;
  118.             }
  119.  
  120.             if ( index > 0 )
  121.             {
  122.                 line.setP1( curve->sample( index - 1 ) );
  123.                 line.setP2( curve->sample( index ) );
  124.             }
  125.         }
  126.     }
  127.  
  128.     return line;
  129. }
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This works and i get always the values from the actual Mouse Position.

Now i want to double Click at a selected position and want the tracker to stay visible also when i move the mouse outside the plot area.

How can i manage this?

Thanks for help

DSP