Re: [PATCH] ui/sdl2: Support multiple OpenGL-enabled windows

[Antonio Caggiano]

Hi Marc-André and Akihiko,

On 07/06/2023 13:24, Akihiko Odaki wrote:
> On 2023/06/07 19:29, Marc-André Lureau wrote:
> > Hi Antonio
> >
> > On Wed, Jun 7, 2023 at 1:13 PM Antonio Caggiano 
> > <quic_acaggian@quicinc.com <mailto:quic_acaggian@quicinc.com>> wrote:
> >
> >     Multiple graphics devices can be defined with an associated OpenGL
> >     enabled SDL console, hence make sure to not destroy their shaders and
> >     windows.
>
> I guess you meant multiple graphics devices can be associated to an 
> OpenGL-enabled console and a switch event from a device destroys the 
> shared state, but I don't see anything that associates multiple devices 
> to a single console.

The idea is to be able to run qemu with OpenGL-enabled SDL windows and 
multiple GPUs [0], e.g.:
-device virtio-vga-gl
-device virtio-vga

[0] 
https://user-images.githubusercontent.com/6058008/244386705-54654833-903e-478a-85f5-d951b7c448b4.mov

> >     Signed-off-by: Antonio Caggiano <quic_acaggian@quicinc.com
> >     <mailto:quic_acaggian@quicinc.com>>
> >     ---
> >       ui/sdl2-gl.c | 2 +-
> >       1 file changed, 1 insertion(+), 1 deletion(-)
> >
> >     diff --git a/ui/sdl2-gl.c b/ui/sdl2-gl.c
> >     index bbfa70eac3..795fb1afc9 100644
> >     --- a/ui/sdl2-gl.c
> >     +++ b/ui/sdl2-gl.c
> >     @@ -89,7 +89,7 @@ void sdl2_gl_switch(DisplayChangeListener *dcl,
> >
> >           scon->surface = new_surface;
> >
> >     -    if (is_placeholder(new_surface) &&
> >     qemu_console_get_index(dcl->con)) {
> >     +    if (is_placeholder(new_surface) && !scon->opengl) {
> >               qemu_gl_fini_shader(scon->gls);
> >               scon->gls = NULL;
> >               sdl2_window_destroy(scon);
> >
> >
> > This was introduced in commit c821a58ee7003c2a0567dddaee33c2a5ae71c404 
> > by Akihiko.
> >
> > Why should the window visibility behaviour be different whether it 
> > uses opengl or not ?
> >
> > If you are fixing a GL/shader crash, maybe it needs to be done 
> > differently.
> >
> > thanks
> It does not make sense to check scon->opengl here; it should be always 
> true when this function is called.
>
> The condition qemu_console_get_index(dcl->con) should not be removed 
> either. This keeps the first console persistent and makes sure the user 
> can always interact with QEMU with the GUI SDL2 provides.

The problem I encounter when adding a second GPUs is that its related 
SDL console gets its window and shaders destroyed, which are definitely 
something I need for rendering it. :D

Do you think where is a better way to avoid that?

> Regards,
> Akihiko Odaki

Cheers,
Antonio Caggiano