Hi Lari!

No, your project file looks good. I was too tired yesterday night. There is a big speed improvement with prerendering. Just set the bool in the code to true. I don't know how I could miss that :-> But it works correctly only up to a seq_lenght of ~1800.

And if compared to a QGraphicsView solution it doesn't gain much, if anything. I'm puzzled. My graphicsview solution crashes (only in release mode) if I try to increase the seq_length to 1900. Don't know whats wrong. That seems to be the same limit, my low-level solution has, before it starts to mess up. So my guess is, that the graphicsview also prerenders the whole item into a displaylist.. hence its excellent performance!

BTW: I'm using Qt4.6 on Win7 with an ATI3850,AMD X2 6000+.

Qt Code: 
  1. #ifndef MAIN_H
  2. #define MAIN_H
  3.  
  4. #include <qapplication.h>
  5. #include <qmainwindow.h>
  6. #include <qgraphicsview.h>
  7. #include <qgraphicsscene.h>
  8. #include <qgraphicsitem.h>
  9. #include <QWheelEvent>
  10. #include <QtOpenGL>
  11. #include <qmath.h>
  12. #include <qcolor.h>
  13.  
  14. using namespace std;
  15.  
  16.  
  17. class SeqMap : public QGraphicsItem
  18. {
  19. public:
  20.     SeqMap(int seq_length = 1500,int num_seq = 80);
  21.     QRectF boundingRect() const{ return QRectF(0, 0, data.at(0).size()*20, data.size()*20); }
  22.  
  23.     void paint(QPainter *painter, const QStyleOptionGraphicsItem *item, QWidget *widget);
  24. private:
  25.     QPixmap* textures[4];
  26.     QVector< QVector<quint8> > data;
  27. };
  28.  
  29.  
  30. class MainWindow : public QMainWindow
  31. {
  32. public:
  33.     MainWindow(QWidget *parent = 0);
  34. private:
  35.     void wheelEvent(QWheelEvent * event);
  36.  
  38.     QGraphicsView *graphicsView;
  39. };
  40.  
  41. /////////////////////
  42.  
  43. SeqMap::SeqMap(int seq_length,int num_seq)
  44. {
  45.      // generate random data to display
  46.     data.reserve(num_seq);
  47.     QVector<quint8> seq0;
  48.     seq0.reserve(seq_length);
  49.     for(int j=0;j<seq_length;j++)
  50.     {
  51.         seq0.push_back( int(rand()/float(RAND_MAX)*4) );
  52.     }
  53.     data.push_back(seq0);
  54.  
  55.     for(int i=1;i<num_seq;i++)
  56.     {
  57.         QVector<quint8> seq_i;
  58.         seq_i.reserve(seq_length);
  59.         for(int j=0;j<seq_length;j++)
  60.         {
  61.             if(rand()/float(RAND_MAX)*20 < 1)
  62.                 seq_i.push_back( int(rand()/float(RAND_MAX)*4) );
  63.             else
  64.                 seq_i.push_back( data.at(0).at(j) );
  65.         }
  66.         data.push_back(seq_i);
  67.     }
  68.  
  69.     QString alpha = "ACGT";
  70.     QColor tile_colors[] = { QColor("blue"), QColor("green"), QColor("yellow"), QColor("red") };
  71.     // Prepare 4 textures
  72.     for (quint8 i=0;i < 4;++i)
  73.     {
  74.         QChar base_char = alpha.at(i);
  75.         QColor color = tile_colors[i];
  76.         QPixmap* pmap = new QPixmap(20,20);
  77.         textures[i] = pmap;
  78.         QPainter painter(pmap);
  79.         QBrush b = painter.brush();
  80.         painter.fillRect(QRectF(0, 0, 20, 20), color);
  81.         painter.setFont(QFont("Times",10));
  82.         painter.setPen(QColor("black"));
  83.         painter.drawText(0, 0, 20, 20,0x0084, QString(base_char));
  84.     }
  85. }
  86.  
  87. void SeqMap::paint(QPainter *painter, const QStyleOptionGraphicsItem *option, QWidget *widget)
  88. {
  89.     Q_UNUSED(widget);
  90.  
  91.     int y_pos = 0;
  92.     for (int i = 0; i < data.size(); i++)
  93.     {
  94.         int x_pos = 0;
  95.  
  96.         for (int j = 0; j < data.at(i).size(); j++)
  97.         {
  98.             int base = data.at(i).at(j);
  99.             painter->drawPixmap(x_pos,y_pos,*textures[base]);
  100.             x_pos += 20;
  101.         }
  102.         y_pos += 20;
  103.     }
  104. }
  105.  
  106. /////////////////////
  107.  
  108. void MainWindow::wheelEvent(QWheelEvent * e)
  109. {
  110.     if ( e->modifiers() == Qt::ControlModifier )
  111.       {
  112.           int numSteps = ( e->delta() / 8 ) / 15;
  113.  
  114.           QMatrix mat = graphicsView->matrix();
  115.  
  116.           if ( numSteps > 0 )
  117.               mat.scale( numSteps * 1.2, numSteps * 1.2 );
  118.           else
  119.               mat.scale( -1 / ( numSteps * 1.2 ), -1 / ( numSteps * 1.2 ) );
  120.  
  121.           graphicsView->setMatrix(mat);
  122.           e->accept();
  123.       }
  124. }
  125.  
  126. MainWindow::MainWindow(QWidget *parent) :
  127.     QMainWindow(parent)
  128. {
  129.  
  130.     // the browser stuff
  131.     scene = new QGraphicsScene();
  132.     scene->addItem(new SeqMap());
  133.  
  134.     graphicsView = new QGraphicsView(this);
  135.     graphicsView->setRenderHint(QPainter::Antialiasing, false);
  136.     graphicsView->setDragMode(QGraphicsView::ScrollHandDrag);
  137.     graphicsView->setOptimizationFlags(QGraphicsView::DontSavePainterState);
  138.     graphicsView->setViewportUpdateMode(QGraphicsView::SmartViewportUpdate);
  139.     graphicsView->setTransformationAnchor(QGraphicsView::AnchorUnderMouse);
  140.     graphicsView->setViewport(new QGLWidget(QGLFormat(QGL::SampleBuffers)));
  141.     graphicsView->setScene(scene);
  142.     graphicsView->setGeometry(QRect(50, 50, 100, 100));
  143.     graphicsView->show();
  144.  
  145.     this->setCentralWidget(graphicsView);
  146.  
  147. }
  148.  
  149. #endif // MAIN_H
  150.  
  151. ---------------------------------
  152.  
  153. #include <QtCore>
  154. #include <QtGui>
  155.  
  156. #include "main.h"
  157.  
  158. int main(int argc, char *argv[])
  159. {
  160.     QApplication a(argc, argv);
  161.  
  162.     MainWindow w;
  163.     w.show();
  164.     return a.exec();
  165. }
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I'll have to leave this to you. Gotta do my stuff now :->

Good luck,

Johannes