[SOLVED] Order of execution of QOffscreenSurface and QOpenGLContex.
I want to draw a image in the QOpenGLFramebufferObject and I use QOffscreenSurface for rendering in another thread without creating a QWindow.
I wrote this part of code for initialize OpenGL context and on Windows all works fine.
m_context = new QOpenGLContext(this);
But on my work Linux PC I have segfault in 2-nd row. And if I swap first two rows and run on Linux all works fine again.
And question is "Why?". It's a bug or maybe I doing something wrong? I didn't find any information about order of execution for surface and context in the documentation.
PS I don't run swapped version on Windows. And don't know whether it work.
Not sure about the crash, but be aware that creating (as in create()) a QOffscreenSurface outside the gui thread is wrong, at least on Windows. This is because on Windows the QOffscreenSuface is nothing but a hidden QWindow and a regular window surface. Creating QWindows outside the gui thread will lead to issues sooner or later so it must be avoided. In fact Qt 5.2.1 and newer will show a warning in this case. On Linux there is no such limitation, though, since there QOffscreenSurface is backed by a GLX or EGL pbuffer surface.
Do you mean that I should run create() from the gui thread and then I can create context object without issues?
Well, like I said I cannot be sure what causes the crash. But in any case, yes, call m_surface.create() on the gui thread instead.
I'd like add that to call create() need after the a.exec() was called.