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

[Elvis Dowson]

Hi,
                            vtkRenderWindow has the following abstract  
methods to retrieve pixel data. Oh, wow, now I get it. Clint, I think  
your approach takes the data from the correct location, anyway, as far  
as blending the vtk OpenGL image data and the Qt generated widget  
image data.

vtkRenderWindow::GetPixelData()
vtkRenderWindow::GetRGBAPixelData()

Hmm, wonder where that leaves us? Check to see if the VTK OpenGL  
pipeline commands work ?

Continuing the analysis..

vtkRenderWindow is implemented by vtkOpenGLRenderWindow, implements  
the GetRGBAPixelData method.


So, here is the interesting stuff, QVTKWidget has two methods


QVTKWidget::saveImageToCache()
QVTKWidget::paintEvent()

which utilises the GetPixelData(), SetPixelData() and  
GetRGBACharPixelData() methods.

When a QVTKWidget::paintEvent() is called, it calls the  
vtkRenderWindow::SetPixelData() to draw the image onto the render  
window. But at this stage it is still very much in the realm of the  
vtk controlled OpenGL render windows, more specifically Carbon or X11  
or Win32 OpenGL rendering contexts.

I'm just thinking out aloud here, we need some way to merge the OpenGL  
pixel data with the Qt generated pixel data, within the QGLWidget  
implementing OpenGL, as a first steps, so that all pixel data  
manipulations are internal to QVTKWidget's implementation, i.e. get  
QVTKWidget to subclass from QGLWidget and add additional methods to  
support merging of the OpenGL generated pixel data from both VTK and  
Qt within the drawBackground() method.

I'm not sure where I'm going with all this, but if you have any  
comments on steering me in the right direction, it will welcome!! :-)

Best regards,

Elvis Dowson