[Qemu-devel] Status of SDL2 and GTK displays: can we make display modular?

[Qemu-devel] Status of SDL2 and GTK displays: can we make display modular?

[Michael Tokarev]

Hello.

What's the current status of SDL2 and GTK support?
Last time I checked and asked, there were some missing
pieces in SDL2 compared with SDL1, basically making
SDL2 unusable (again, compared with SDL1).

GTK backend, besides the menu, does not add any noticeable
functionality to SDL1 interface, but adds a lot of extra
dependencies.  This, and also the fact that at least
initial GTK support was incomplete, was the reasons why
in Debian we didn't change default display backend from
SDL1 to GTK when qemu changed the default.

Now I wonder if we can finally switch to SDL2 and/or to
GTK, and maybe even make the display backend dynamically
loadable in the same way as block device backends are
these days.

With loadable display backend it will be the last bastion
for many people who are asking for "minimal QEMU for
servers" which is supposed to not have any X deps.
I started working on loadable display backend a few
years ago, but quickly discovered that SDL1 can't be
loaded dynamically, at least on some platforms where
it substitutes main() function in order to do some
initialization (as if there's no support for constructors).

So now I'm asking again whenever current GTK and SDL2
supports are complete enough to replace SDL1.

Thanks,

/mjt

Re: [Qemu-devel] Status of SDL2 and GTK displays: can we make display modular?

[Paolo Bonzini]

On 22/06/2015 14:00, Michael Tokarev wrote:
> With loadable display backend it will be the last bastion
> for many people who are asking for "minimal QEMU for
> servers" which is supposed to not have any X deps.
> I started working on loadable display backend a few
> years ago, but quickly discovered that SDL1 can't be
> loaded dynamically, at least on some platforms where
> it substitutes main() function in order to do some
> initialization (as if there's no support for constructors).
> 
> So now I'm asking again whenever current GTK and SDL2
> supports are complete enough to replace SDL1.

SDL2 audio is broken, so strictly speaking no.

Paolo

Re: [Qemu-devel] Status of SDL2 and GTK displays: can we make display modular?

[Gerd Hoffmann]

  Hi,

> With loadable display backend it will be the last bastion
> for many people who are asking for "minimal QEMU for
> servers" which is supposed to not have any X deps.

> I started working on loadable display backend a few
> years ago, but quickly discovered that SDL1 can't be
> loaded dynamically, at least on some platforms where
> it substitutes main() function in order to do some
> initialization (as if there's no support for constructors).
> 
> So now I'm asking again whenever current GTK and SDL2
> supports are complete enough to replace SDL1.

I don't miss any features in sdl2/gtk.

I think gtk should work reasonable well meanwhile as it is the default
and thus used alot.

Not so sure about sdl2.  sdl1 is still the default, so I don't think
there are that many users of it, which increases the chance that there
are unnoticed bugs and regressions lurking ...

Loadable display modules are worth looking into nevertheless.  We need
some kind of interface to register UIs, simliar to blockdevs and
devices.  But we have interesting constrains here:

 * You can have multiple UIs active at the same time (gtk+vnc).
 * That doesn't work for every combination though (no gtk+sdl).
 * There are deps to other stuff such as audio (sdl+spice) and
   display (spice/qxl).

So getting that modeled right isn't that easy and straightforward.

If you wanna have a look nevertheless you are welcome ...

cheers,
  Gerd