Hello everybody,

i have a large Qt (4.8.4 / linux, opensuse) code which displays some data. I need to extend the main display window by adding axis scale. This window has a zoom (through mouse wheel), so the scale must adapt depending on the zoom. I read qwt (6.1) is appropriate for this task. I am performing some simple tests with qwt on a simplified code, but i am not able to display this scale using QwtPlotScaleItem, although I am successful at using qwt to display some curves !.

Can you tell me what I am doing wrong with the scale ?

Here is a section of the code ...

Qt Code: 
  1. //Set scene, pixmap and get an image of the data
  2.             scene = new QGraphicsScene(this);
  3.             pixmapItem = new QGraphicsPixmapItem();
  4.             scene->addItem(pixmapItem);
  5.  
  6.             view = new QGraphicsView();
  7.             view->setScene(scene);
  8.  
  9.             setCentralWidget(view);
  10.  
  11.             imageSrc = new ImageSource();
  12.             pixmapItem->setPixmap(*imageSrc->nextImage());
  13.  
  14.             QImage* imagerectangle;
  15.             imagerectangle = new QImage(27500,250,QImage::Format_ARGB32);
  16.             imagerectangle->fill(qRgba(0, 0, 0, 0));
  17.  
  18.             // Set a Qpainter
  19.             QPainter* rectangle;
  20.             rectangle = new QPainter(imagerectangle);
  21.  
  22.             //Pen properties
  23.             QPen lepen;
  24.             QRectF rect(5000,100,3000,50);
  25.             lepen.setColor(Qt::red);
  26.             lepen.setWidth(10);
  27.  
  28.  
  29.             // TEST QWT: OK work -> a curve is displayed *****************************
  30.             QwtPlotCurve d_curves;
  33.  
  34.             xMap.setScaleInterval(0, 10000);
  35.             yMap.setScaleInterval(0, 250);
  36.  
  37.             // Calculate values
  38.             double xval[10000];
  39.             double yval[10000];
  40.             for(int i=0; i<10000;i++)
  41.             {
  42.                 xval[i] = i;
  43.                 yval[i] = qSin(xval[i]) * qCos(2.0 * xval[i]) * 100 +101;
  44.             }
  45.  
  46.             d_curves.setPen(QColor(Qt::yellow));
  47.             d_curves.setStyle(QwtPlotCurve::Lines);
  48.             d_curves.setRenderHint(QwtPlotItem::RenderAntialiased);
  49.             d_curves.setCurveAttribute(QwtPlotCurve::Fitted);
  50.  
  51.             d_curves.setRawSamples(xval, yval, 10000);
  52.  
  53.             const QRect &r = contentsRect();
  54.  
  55.             xMap.setPaintInterval(r.left(), r.right());
  56.             yMap.setPaintInterval(r.top(), r.bottom());
  57.  
  58.             d_curves.draw(rectangle, xMap, yMap, r);
  59.             d_curves.show();
  60.             // So far this is good ! ************************************************
  61.  
  62.  
  63.             // add a scale to the plot. DOES NOT WORK nothing is displayed ????????????
  64.             QwtPlotScaleItem* echelle;
  65.             echelle = new QwtPlotScaleItem();
  66.             echelle->setAlignment(QwtScaleDraw::TopScale);
  67.             echelle->setBorderDistance(0);
  68.             echelle->scaleDraw()->setTickLength(QwtScaleDiv::MajorTick,100);
  69.             echelle->scaleDraw()->setTickLength(QwtScaleDiv::MinorTick,50);
  70.             echelle->scaleDraw()->enableComponent(QwtAbstractScaleDraw::Labels,true);
  71.             rectangle->setRenderHint(QPainter::Antialiasing,
  72.                         echelle->testRenderHint(QwtPlotItem::RenderAntialiased) );
  73.             echelle->setVisible(TRUE);
  74.             echelle->draw(rectangle,xMap,yMap,r);
  75.             echelle->show();
  76.             // what is wrong here ??????????????????????
  77.  
  78.  
  79.            // add to scene
  80.            scene->addPixmap(QPixmap::fromImage(*imagerectangle));
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Thank you very much for your help !

Val