Re: [Qemu-devel] [PATCH v2 4/5] gtk: add opengl support, using egl

[Max Reitz <mreitz@redhat.com>]

On 20.05.2015 17:19, Gerd Hoffmann wrote:
> This adds opengl rendering support to the gtk ui, using egl.
> It's off by default for now, use 'qemu -display gtk,gl=on'
> to play with this.
>
> Note that gtk got native opengl support with release 3.16.
> There most likely will be a separate implementation for 3.16+,
> using the native gtk opengl support.  This patch covers older
> versions (and for the time being 3.16 too, hopefully without
> rendering quirks).
>
> Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
> ---
>   include/ui/console.h |   2 +-
>   include/ui/gtk.h     |  23 +++++++++
>   ui/Makefile.objs     |   3 ++
>   ui/gtk-egl.c         | 141 +++++++++++++++++++++++++++++++++++++++++++++++++++
>   ui/gtk.c             |  77 ++++++++++++++++++++++------
>   vl.c                 |  11 +++-
>   6 files changed, 240 insertions(+), 17 deletions(-)
>   create mode 100644 ui/gtk-egl.c

I do see the quandary with gtk 3.14 and 3.15 
(gtk_widget_set_double_buffered() is deprecated, but we need it), but 
the problem is, with this patch, you simply cannot compile qemu on a gtk 
3.14+ system with --with-gtkabi=3.0 and without --disable-opengl, which 
I don't think is right.

So at least the commit message is wrong, this patch does not cover 3.16. 
It would without -Werror (or with -Wno-deprecated-declarations), but 
that's enabled by default.

Once the native OpenGL support introduced by 3.16 is used, at least 
that'll be covered, but we'll still have to deal with 3.14 and 3.15. I 
think the right thing to do is to make configure disable OpenGL support 
if gtk 3.14+ is to be used (in the future, that would be 3.14/3.15 
only). That, or pass -Wno-deprecated-declarations for compiling 
ui/gtk.c, but that seems very ugly to me.

Not planning to have OpenGL support for 3.14/3.15 I think is fine, but 
we have to make sure that OpenGL support cannot be silently enabled by 
configure and then break compilation of qemu.

Max