Hi all,

i have a little probelm. I wanted to write a renderer and use qt as a frontend. Now my question is, how do i display and update my image _efficently_. As the rendering process needs time there are only a few pixels which gets updated in a certain interval.

I've written a little program which shows how i would solve this problem. But i'm not very happy with this solution because i don't know how much copying of the image is done under the hood. Maybe theres a better way?

Here the code:

Qt Code: 
  1. class QMainWin : public QMainWindow
  2. {
  3.     Q_OBJECT
  4.  
  5. public:
  6.     QMainWin();
  7.  
  8. private:
  9.     QScrollArea *area;
  10.     QImage *image;
  11.     QLabel *imgLabel;
  12.     int x, y;
  13.  
  14. private slots:
  15.     void drawPixels();
  16. };
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Qt Code: 
  1. QMainWin::QMainWin()
  2. {
  3.     image = new QImage(200, 200, QImage::Format_ARGB32);
  4.     imgLabel = new QLabel;
  5.     imgLabel->setPixmap(QPixmap::fromImage(*image));
  6.  
  7.     area = new QScrollArea;
  8.     area->setBackgroundRole(QPalette::Dark);
  9.     area->setWidget(imgLabel);
  10.  
  11.     setCentralWidget(area);
  12.  
  13.     QAction* action = new QAction(tr("Draw something"), this);
  14.     connect(action, SIGNAL(triggered()), this, SLOT(drawPixels()));
  15.  
  16.     QMenu* menu = menuBar()->addMenu(tr("Drawing"));
  17.     menu->addAction(startAction);
  18.  
  19.     x = y = 0;
  20. }
  21.  
  22. void QMainWin::drawPixels()
  23. {
  24.     for(int i = y; i < y+20; i++)
  25.         for(int j = x; j < x+20; j++)
  26.             image->setPixel(j, i, qRgb(255, 0, 0));
  27.  
  28.     x += 20;
  29.     y += 20;
  30.  
  31.     // This line is needed, else the picture doesn't get updated
  32.     imgLabel->setPixmap(QPixmap::fromImage(*image));
  33.     imgLabel->update();
  34. }
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I've omitted forward declarations, includes and so on.
Sry for the bad english.

Regards
Imons