[Interest] Problem with float texture rendering in QOpenGLWidget on Ivy Bridge/Haswell Intel GPUs on Windows

[Elvis Stansvik]

This may or may not be a Qt issue.

I'm trying to help the VTK folks narrow down a problem with their new
QVTKOpenGLWidget, which is a newly-introduced QOpenGLWidget-based
class for letting VTK render into a QOpenGLWidget.

The problem manifests itself as volume renderings not showing up on
Windows machines with Ivy Bridge (e.g HD4000) and Haswell (e.g.
HD4600) Intel GPUs when using the new class. VTKs volume rendering is
done using float textures.

Volume renderings works fine on the same machines when using "plain"
VTK. This is when VTK itself sets up the OpenGL context (using GLEW I
believe), but apart from that, the rendering pipeline is exactly the
same I think. This is what leads me to believe that the issue is
something specific to QOpenGLWidget, or to how VTK uses it.

VTK requests a OpenGL 3.2 core context, and through some debugging,
I've verified that VTK is actually getting the context that it is
requesting.

The issue is reported by me, here at VTKs GitLab:

   https://gitlab.kitware.com/vtk/vtk/issues/17058

The report contains some more information, such as the generated
fragment shader that VTKs volume rendering backend is using, and a GL
report from the problematic machine.

Does this specific issue (float texture rendering not showing up on
these semi-old Intel GPUs) ring a bell to anyone else?

Many thanks for any tips/pointers/leads on how to debug this.

I'm really interested in getting this issue in VTK fixed, since
laptops with these GPUs are quite common. It's also affecting recent
versions of ParaView, which has (just like me) recently ported to the
new QVTKOpenGLWidget.

Elvis