[Octave-bug-tracker] [bug #44478] test __osmesa_print__.cc-tst crashes on Ubuntu with Nvidia drivers

[Michael Goffioul]

Follow-up Comment #53, bug #44478 (project octave):

@Rik: Making the OpenGL context current is the responsibility of the
underlying toolkit (Qt or FLTK). The toolkit takes care of creating the
context and making it current in the current thread, so you can start issuing
OpenGL commands. In Qt, you only override QGLWidget::paintGL; as doc says in
http://doc.qt.io/qt-4.8/qglwidget.html#paintGL the context has been made
current for you. The same system exists for FLTK (as in other UI toolkit).

About the question concerning FLTK and OSMesa, I don't know. Looking at the
code, __osmesa__print__ creates its own context and makes it current before
issuing other OpenGL commands. I'm not familiar with OSMesa, but I'd expect it
to be independent of the toolkit used. My point was that your simple example
might not show the same type of error as reported initially in this bug
report.

@Andreas: The point is a current context in the current thread. When you use
Qt, you create a current context in Qt's eventloop thread, not in octave
thread. When you run simple_gl_oct, there is no valid context in octave
thread. When you use FLTK, the eventloop *is* the octave thread, so after the
"sombrero" call, there is a current context in the octave thread, the one that
was used to plot the figure.


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