I have a QGraphicsView and on this view I place several subclassed QGraphicsItems which implement their own paint method. Now I want to render the graphicsview/scene to an image and save this to disk. I use the following method to render the scene to an image:

Qt Code: 
  1. QPainter *pngPainter = new QPainter();
  2. QImage *image = new QImage(QSize(width,height), QImage::Format_ARGB32_Premultiplied);
  3.  
  4. pngPainter->begin(image);
  5.   pngPainter->setRenderHint(QPainter::Antialiasing);
  6.   _ui->graphicsView->scene()->render(pngPainter);
  7. pngPainter->end();
  8. image->save(fileName);
  9.  
  10. delete pngPainter;
  11. delete image;
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This works perfectly when I use QPainter commands in the paint procedure of the QGraphicsItems, like so (block is a QRectF):

Qt Code: 
  1. void CNodeGraphicsItem::paint(QPainter *painter, const QStyleOptionGraphicsItem *option, QWidget *widget)
  2. {
  3.    // color setup
  4.    painter->setPen(Qt::red);
  5.    painter->setBrush(Qt::red);
  6.  
  7.    painter->drawRect(block);
  8. }
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However, If (for performance reasons and in order to use shaders) I use native opengl commands, like so:

Qt Code: 
  1. void CNodeGraphicsItem::paint(QPainter *painter, const QStyleOptionGraphicsItem *option, QWidget *widget)
  2. {
  3.    painter->beginNativePainting();
  4.    glBegin(GL_QUADS);
  5.      setGLColor(Qt::red); // Own function to set glColor3f;
  6.      glTexCoord2f (0.0, 0.0);glVertex2d(block.left(),block.top());
  7.      glTexCoord2f (1.0, 0.0);glVertex2d(block.right(),block.top());
  8.      glTexCoord2f (1.0, 1.0);glVertex2d(block.right(),block.bottom());
  9.      glTexCoord2f (0.0, 1.0);glVertex2d(block.left(),block.bottom());
  10.   glEnd();
  11.   painter->endNativePainting();
  12. }
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It no longer works and the output is an entire black image. The rendering on the QGraphicsView gives the expected result though (a red rectangle). Any ideas on how to solve this / make it work with native opengl commands?

I know I can grab the framebuffer:
Qt Code: 
  1. QImage img = ((QGLWidget*)_ui->graphicsView->viewport())->grabFrameBuffer(true);
  2.   img.save(fileName, "PNG", 100);
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This works, however the output image is only the size of the graphicsView, I want to be able
to output high-res images.