[Octave-bug-tracker] [bug #63748] Qt graphics toolkit cannot create OpenGL rendering context

[anonymous]

Follow-up Comment #13, bug #63748 (project octave):

After some efforts I found this web page [1] from Qt project. It is noted that
the mechanism of loading OpenGL driver is changed. From the instructions I can
set these environment variables to force Qt to load software renderer.

set QT_OPENGL=software
set QT_OPENGL_DLL=opengl32.dll


The other problem is the opengl32.dll that is shipped with Octave 8.0.90 that
wouldn't work on Windows7 and prevents the Octave program from starting. So we
need to find a working dll like the one that is suggested in comment #8 or
copy it from previous Octave versions.

Now everything is OK. I attached screenshot of the imshow(1) command. 

Responding to comment #12 
The main problem is that "m_os_context" is a pointer to a QOpenGLContext
object that never is constructed. I cannot find any "new QOpenGLContext"
expression in the GLCanvas.cc. Because GLCanvas is subclass of QOpenGLWidget
and QOpenGLWidget  itself has a QOpenGLContext as its private member the
OpenGL driver uses that context. However if that context for some reasons
becomes invalid it appears that GLCanvas switches to m_os_context  that isn't
constructed.


[1] https://doc.qt.io/qt-5/windows-requirements.html

(file #54321)

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