Hello,
I want to visualize a flowing data with a bar graph. Ive written a test code; but i see some flickers when the graph is being drawn. I know that double buffering is default with qt4. What should I do else to remove the flickers on the screen? The code is below:

main.cpp:
Qt Code: 
  1. int main(int argc, char *argv[])
  2. {
  3. #include <QApplication>
  4. #include "anapencere.h"
  5. #include <QGraphicsView>
  6.  
  7.     QApplication a(argc, argv);
  8.     AnaPencere mAnapencere;
  10.     mAnapencere.setSceneRect(0,0,400,250);
  11.     view.setScene(&mAnapencere);
  12.     view.show();
  13.     return a.exec();
  14. }
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anapencere.h :
Qt Code: 
  1. #ifndef ANAPENCERE_H
  2. #define ANAPENCERE_H
  3.  
  4. #include <QGraphicsScene>
  5. #include <QTimer>
  6. #include "bargrapher.h"
  7. #include <sys/time.h>
  8.  
  9. class AnaPencere : public QGraphicsScene
  10. {
  11.     Q_OBJECT
  12. public:
  13.     explicit AnaPencere(QObject *parent = 0);
  14.  
  15. private:
  16.     QTimer mTimer;
  17.     BarGrapher *grapher;
  19.     int mCurrentTime;
  20.     int mPrevTime;
  21.     int differ;
  22.     int fps;
  23.     int textPrinter;
  24.     struct timeval tv;
  25.  
  26. private slots:
  27.     void updateSlot();
  28.  
  29. };
  30.  
  31. #endif // ANAPENCERE_H
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bargrapher.h
Qt Code: 
  1. #ifndef BARGRAPHER_H
  2. #define BARGRAPHER_H
  3.  
  4. #include <QGraphicsItem>
  5. #include <QList>
  6.  
  7. class BarGrapher : public QGraphicsItem
  8. {
  9. public:
  10.     BarGrapher();
  11.     QRectF boundingRect() const;
  12.     void paint(QPainter *painter, const QStyleOptionGraphicsItem *option, QWidget *widget);
  13.     void insertData(qreal data );
  14. private:
  15.     QList<int> floatingData;
  16. };
  17.  
  18. #endif // BARGRAPHER_H
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anapencere.cpp :
Qt Code: 
  1. #include "anapencere.h"
  2.  
  3. AnaPencere::AnaPencere(QObject *parent) :
  5. {
  6.     connect(&mTimer,SIGNAL(timeout()),this,SLOT(updateSlot()));
  7.     grapher= new BarGrapher();
  8.     addItem(grapher);
  9.     fpsText= new QGraphicsTextItem;
  10.     fpsText->setPlainText("0");
  11.     addItem(fpsText);
  12.     mPrevTime=0;
  13.     mCurrentTime=0;
  14.     textPrinter=0;
  15.     mTimer.start(40);
  16. }
  17.  
  18. void AnaPencere::updateSlot()
  19. {
  20.     grapher->insertData(rand()%200);
  21.     grapher->update();
  22.  
  23.     textPrinter++;
  24.     gettimeofday(&tv,NULL);
  25.     mPrevTime=mCurrentTime;
  26.     mCurrentTime = tv.tv_sec % 100000 * 1000;
  27.     mCurrentTime += tv.tv_usec/1000 ;
  28.     differ= mCurrentTime-mPrevTime;
  29.     if(differ!=0)
  30.         fps=1000/(differ);
  31.     else fps=1000;
  32.  
  33.     if(textPrinter%100==0){
  34.         fpsText->setPlainText(QString::number(fps)+" fps");
  35.         textPrinter=0;
  36.     }
  37. }
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bargrapher.cpp
Qt Code: 
  1. #include "bargrapher.h"
  2. #include <QPainter>
  3.  
  4. BarGrapher::BarGrapher()
  5. {
  6. }
  7. QRectF BarGrapher::boundingRect() const
  8. {
  9.     return QRectF(0, 0,400, 250);
  10. }
  11.  
  12. void BarGrapher::paint(QPainter *painter, const QStyleOptionGraphicsItem *option,
  13.                      QWidget *widget)
  14. {
  15.     painter->setPen(Qt::black);
  16.     painter->setBrush(QBrush(Qt::red));
  17.     painter->fillRect(QRect(0,0,400,250),Qt::green);
  18.     for(int i=0;i<floatingData.size();++i)
  19.     {
  20.         painter->drawRect(0,floatingData.at(i),10,300);
  21.         painter->translate(10,0);
  22.     }
  23.     if(floatingData.size()>=50)
  24.         floatingData.takeFirst();
  25.  
  26. }
  27.  
  28. void BarGrapher::insertData(qreal data)
  29. {
  30.     floatingData.append((int)data);
  31. }
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