Bug#1020937: libgtk-3-0: fix gl on GLES-only platforms

[Simon McVittie]

On Thu, 19 Jan 2023 at 14:12:28 +0900, Dominique Martinet wrote:
> Just a follow-up on this proposed updates mechanism -- it looks like
> this wasn't included in the december 11.6 point update (as expected,
> since we agreed to let it be tested for a bit), is there anything I
> should/can do to make sure the next 11.7 gets gtk+3.0 3.24.34-5, or is
> that still too early?

11.7 will not get gtk+3.0_3.24.34-5, regardless. The changes between
3.24.24 and 3.24.34 are too extensive to ask the release team to review
them (1242 lines of changes in gtk/gtkimcontextsimple.c alone) and have
triggered serious regressions in the past, although I hope all the known
regressions are now fixed for Debian 12.

What *could* go into either 11.7 or a later 11.x point release is a
version derived from the version 3.24.24-4+deb11u2 currently in stable,
with the change that fixes GLES-only platforms applied as a patch. It
would end up versioned as 3.24.24-4+deb11u3, unless it gets preempted
by an urgent security fix or something like that.

Is upstream commit 0e5fe45ea20cce074a128911949dbedf4f8265bf, from
<https://gitlab.gnome.org/GNOME/gtk/-/merge_requests/5062>, necessary
and sufficient to fix this in the 3.24.24 codebase? Or are there other
changes required?

If upstream !5062 is believed to be sufficient, please try building
<https://salsa.debian.org/gnome-team/gtk3/-/merge_requests/13>
(it can be built with git-buildpackage, or let me know if you need a
complete source package), and verify that it solves the problem for you
on your GLES-only device(s)/driver(s).

Also, please check that what I've written in the changelog is accurate.
I don't think I had fully realised until I looked again at this patch
that while your bug report talks about GTK failing to use GL on GLES-only
platforms and doesn't mention X11 vs. Wayland, your patch only changes
the Wayland code path. From a quick look at gdk/x11/gdkglcontext-x11.c,
it seems your change is making the Wayland/EGL code path match what
X11/GLX already did, and so you could have worked around this bug with
GDK_BACKEND=x11, except that presumably you'd prefer to have the benefits
of using native Wayland?

The other testing that is needed on this version is to confirm that
it doesn't break anything on Debian 11 systems where "desktop" OpenGL
*is* available, such as ordinary x86 PCs, and presumably also embedded
systems that use Mesa (such as the etnaviv driver). I can try it on x86,
but any testing you can do on this would also improve our confidence
about this backport.

Thanks,
    smcv