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

[Markus Mützel]

Follow-up Comment #14, bug #63748 (project octave):

Do you still need to set those environment variables now that you found an
`opengl32.dll` library that works for you?


> 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.

`m_os_context` is not a pointer. It is an object of type QOpenGLContext:
https://hg.savannah.gnu.org/hgweb/octave/file/74aa32d5fd08/libgui/graphics/GLCanvas.h#l98

  QOpenGLContext m_os_context;


IIUC, it is "always constructed" (with the default constructor). See:
https://doc.qt.io/qt-6/qopenglcontext.html#QOpenGLContext

> 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.

Are you saying that `GLCanvas` isn't using the `QOpenGLContext` instantiated
in `m_os_context` but some other context? Would we need to "assign"
`m_os_context` as a context for `GLCanvas` somehow?


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