Re: Gtk::GLArea throws "Couldn't find current GLX or EGL context.\n"' on unrealizing

[Gerlof Fokkema <gerlof fokkema gmail com>]

Dear list,

I did some more digging and found that there is no context associated
to Gtk::GLArea anymore when signal_unrealize is triggered.
I assume that somewhere between calling the Gtk::GLArea destructor and
signal_unrealize the GL context is already unset:

https://gist.github.com/gfokkema/a0c73de5c9df476b5b31057ebb63394f/revisions
> ┌─gerlof@gerlof-laptop ~/workspace/build-gtk-renderer-Desktop-Debug $
> └─╼./example
> Realize context: 0x55ed5dfa7590
> Destructor context: 0x55ed5dfa7590
> Unrealize context: (nil)
> example: ../libepoxy/src/dispatch_common.c:863: epoxy_get_proc_address: Assertion `0 && "Couldn't find 
> current GLX or EGL context.\n"' failed.
> Aborted (core dumped)

After setting breakpoints in `gtk_gl_area_dispose` and
`gtk_gl_area_unrealize`, this makes sense:

First gtk_gl_area_dispose is called, which clears the context:
https://gitlab.gnome.org/GNOME/gtk/blob/3.24.13/gtk/gtkglarea.c#L200
1 gtk_gl_area_dispose
gtkglarea.c  200 0x7ffff716d628
2 g_object_run_dispose
                0x7ffff68a471a
3 Gtk::Object::_release_c_instance()
                0x7ffff7cc69e9
4 Gtk::GLArea::~GLArea()
                0x7ffff7c1fbad
5 Example::~Example
example.cpp  65  0x555555560dbc
6 Example::~Example
example.cpp  71  0x555555560e38
7 std::default_delete<Example>::operator()
unique_ptr.h 81  0x555555561d38
8 std::unique_ptr<Example, std::default_delete<Example>>::~unique_ptr
unique_ptr.h 284 0x555555561a9c
9 main
example.cpp  127 0x5555555614af

And then afterwards, gtk_gl_area_unrealize is called, which clears the
context again?
https://gitlab.gnome.org/GNOME/gtk/blob/3.24.13/gtk/gtkglarea.c#L593
1  gtk_gl_area_unrealize
        gtkglarea.c    580   0x7ffff7175721
2  g_closure_invoke
        gclosure.c     810   0x7ffff68a2d5a
3  signal_emit_unlocked_R
        gsignal.c      3679  0x7ffff688fff8
4  g_signal_emit_valist
        gsignal.c      3397  0x7ffff689498a
5  g_signal_emit
        gsignal.c      3453  0x7ffff68957f0
6  gtk_widget_unrealize
        gtkwidget.c    5578  0x7ffff6fea3b6
7  gtk_widget_unparent
        gtkwidget.c    4670  0x7ffff6feae66
8  gtk_bin_remove
        gtkbin.c       151   0x7ffff725043a
9  Gtk::Container_Class::remove_callback_normal(_GtkContainer *,
_GtkWidget *)                      0x7ffff7bff3ee
10 g_cclosure_marshal_VOID__OBJECTv
        gmarshal.c     1910  0x7ffff68a47d0
11 _g_closure_invoke_va
        gclosure.c     873   0x7ffff6894b4a
12 g_signal_emit_valist
        gsignal.c      3306  0x7ffff6894b4a
13 g_signal_emit
        gsignal.c      3453  0x7ffff68957f0
14 gtk_container_remove
        gtkcontainer.c 1906  0x7ffff7201f9a
15 gtk_widget_dispose
        gtkwidget.c    12151 0x7ffff6fe1275
16 g_object_run_dispose
        gobject.c      1130  0x7ffff68a471a
17 Gtk::Object::_release_c_instance()
                             0x7ffff7cc69e9
18 Gtk::GLArea::~GLArea()
                             0x7ffff7c1fbad
19 Example::~Example
        example.cpp    65    0x555555560dbc
20 Example::~Example
        example.cpp    71    0x555555560e38
21 std::default_delete<Example>::operator()
        unique_ptr.h   81    0x555555561d38
22 std::unique_ptr<Example, std::default_delete<Example>>::~unique_ptr
        unique_ptr.h   284   0x555555561a9c
23 main
        example.cpp    127   0x5555555614af

Something doesn't seem right in the order of disposal of GtkGLArea.

Regards,
Gerlof Fokkema