[vtk-developers] Transparency/depth peeling with Python and Qt on Linux

[Prabhu Ramachandran]

Hi all,

Some folks have been running into strange rendering issues with the Qt Render
window interactor in Python, on Linux, with transparent actors.  I've reduced
this to two scripts that I attach which just require VTK-Python.  The first is
with pure VTK and which seems to work fine and the second is with the
QVTKRenderWindowInteractor which fails.

The script just creates two semi-transparent spheres one next to the other and
turns on depth peeling. When the example fails, the blue ball can never be seen
in front of the red one.  This example works fine with VTK 8.1.1 on Mac OSX but
fails on Linux (ubuntu 16.04 and 18.04).  The non pyqt one works just fine.  I
did try experimenting with using QGLWidget and also with using the newer
QOpenGLWidget but they both display the same issue on Linux it seems like.

Have any of you seen this before?  The blog post here:
https://blog.kitware.com/vtk-8-0-0/ suggests there are some transparency issues
with the C++ widget as well but I am not sure if those are already resolved. 
Any thoughts or pointers on this?

Thanks!

cheers,

Prabhu


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