[vtkusers] How to put Qt widgets on top of a VTK OpenGL scene

[Elvis Dowson]

Hi,
         I did a little bit more digging around the sources and found  
the following pieces of information.

Qt 4.4.3: QGLWidget Class Reference

QGLWidget provides functionality for displaying OpenGL graphics  
integrated into a Qt application. It is very simple to use. You  
inherit from it and use the subclass like any other QWidget, except  
that you have the choice between using QPainter and standard OpenGL  
rendering commands.

If you look at the QVTKWidget class, it inherits from QWidget and uses  
the QPainter class to render images onto the window. Correct me if I'm  
wrong, but if we replace this with standard OpenGL rendering commands,  
we should be able to get a performance increase in rendering VTK when  
using it with Qt.

void QVTKWidget::paintEvent(QPaintEvent* )
{

..

   // In Qt 4.1+ let's support redirected painting
#if QT_VERSION >= 0x040100
   // if redirected, let's grab the image from VTK, and paint it to  
the device
   QPaintDevice* device = QPainter::redirected(this);
   if(device != NULL && device != this)
     {
     int w = this->width();
     int h = this->height();
     QImage img(w, h, QImage::Format_RGB32);
     vtkUnsignedCharArray* pixels = vtkUnsignedCharArray::New();
     pixels->SetArray(img.bits(), w*h*4, 1);
     this->mRenWin->GetRGBACharPixelData(0, 0, w-1, h-1, 1, pixels);
     pixels->Delete();
     img = img.rgbSwapped();
     img = img.mirrored();

     QPainter painter(this);
     painter.drawImage(QPointF(0.0,0.0), img);
     return;
     }
#endif
}


..
}

Best regards,

Elvis Dowson

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