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

Elvis Stansvik elvstone at gmail.com
Wed Jun 21 11:44:08 CEST 2017

2017-06-21 11:38 GMT+02:00 Elvis Stansvik <elvstone at gmail.com>:
> 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.

I should clarify: I mean the rendering pipeline for volume rendering
in VTK is exactly the same when using "plain" (non-Qt) VTK (which
works), as when using QVTKOpenGLWidget. The only difference (AFAIK) is
in how the OpenGL context is set up (GLEW or QOpenGLWidget).

(The VTK issue I linked also has a minimal VTK testcase I wrote, where
you can switch between using QVTKOpenGLWidget or plain VTK rendering
by passing or not passing a command line parameter).


> 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

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