[vtkusers] QVTKOpenGLWidget and Qt's dynamic selection of OpenGL backend in Qt

[Oleg Gubanov]

Hi,

Since version 5.4, Qt applications based on class `QOpenGLWidget` select
OpenGL dynamically at runtime: in addition to using actual OpenGL
implementation, Qt may choose software rendering or even translate
OpenGL API calls to DirectX calls. This choice can be manually
overridden by setting environment variable `QT_OPENGL=software` or
`QT_OPENGL=angle`. For details, please see
<
http://blog.qt.io/blog/2014/11/27/qt-weekly-21-dynamic-opengl-implementation-loading-in-qt-5-4/
>.

Considering that Qt's class `QOpenGLWidget` is used by VTK's class
`QVKTOpenGLWidget`, how does the latter class account for Qt's switch to
`software` and `angle` OpenGL backends?

Does VTK provide an OpenGL abstraction layer similar to Qt's? Does
`QVTKOpenGLWidget` direct OpenGL calls to `QOpenGLFunctions`, taking
advantage of Qt's dynamic selection of OpenGL backend? If no, are there
any plans to go in that direction?

Thanks,
Oleg.
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