Re: [PULL 2/5] ui/gtk-egl: Check EGLSurface before doing scanout

[Volker Rümelin]

>> From: Antonio Caggiano <quic_acaggian@quicinc.com>
>>
>> The first time gd_egl_scanout_texture() is called, there's a possibility
>> that the GTK drawing area might not be realized yet, in which case its
>> associated GdkWindow is NULL. This means gd_egl_init() was also skipped
>> and the EGLContext and EGLSurface stored in the VirtualGfxConsole are
>> not valid yet.
>>
>> Continuing with the scanout in this conditions would result in hitting
>> an assert in libepoxy: "Couldn't find current GLX or EGL context".
>>
>> A possible workaround is to just ignore the scanout request, giving the
>> the GTK drawing area some time to finish its realization. At that point,
>> the gd_egl_init() will succeed and the EGLContext and EGLSurface stored
>> in the VirtualGfxConsole will be valid.
>>
>> Signed-off-by: Antonio Caggiano <quic_acaggian@quicinc.com>
>> Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>
>> Message-Id: <20231016123215.2699269-1-quic_acaggian@quicinc.com>
>> ---
>>  ui/gtk-egl.c | 17 ++++++++++++-----
>>  1 file changed, 12 insertions(+), 5 deletions(-)
> Hi Antonio,
>
> this patch breaks the QEMU guest display on my system. QEMU was started
> with ./qemu-system-x86_64 -machine q35 -device
> virtio-vga-gl,xres=1280,yres=768 -display gtk,zoom-to-fit=off,gl=on. I
> can see the OVMF boot screen and then GRUB. After Linux was started,
> plymouth normally shows the OVMF boot logo and a rotating spinner. With
> your patch the guest screen is black and shows 'Display output is not
> active.'. It seems the guest works without issues. I can use ssh to log
> in and I can't find any obvious errors in the guest log files. The host
> uses a GNOME desktop under X11.
>
> If I revert this patch everything works as expected.
>
> With best regards,
> Volker
>
> Cc: Michael Tokarev
> This will affect Stable-7.2.7 and Stable-8.1.3.
>
>> diff --git a/ui/gtk-egl.c b/ui/gtk-egl.c
>> index a1060fd80f..3e8d1c1d02 100644
>> --- a/ui/gtk-egl.c
>> +++ b/ui/gtk-egl.c
>> @@ -243,12 +243,19 @@ void gd_egl_scanout_texture(DisplayChangeListener *dcl,
>>      vc->gfx.h = h;
>>      vc->gfx.y0_top = backing_y_0_top;
>>  
>> -    eglMakeCurrent(qemu_egl_display, vc->gfx.esurface,
>> -                   vc->gfx.esurface, vc->gfx.ectx);
>> +    if (!vc->gfx.esurface) {
>> +        gd_egl_init(vc);
>> +        if (!vc->gfx.esurface) {
>> +            return;
>> +        }
>> +
>> +        eglMakeCurrent(qemu_egl_display, vc->gfx.esurface,
>> +                       vc->gfx.esurface, vc->gfx.ectx);
>>  
>> -    gtk_egl_set_scanout_mode(vc, true);
>> -    egl_fb_setup_for_tex(&vc->gfx.guest_fb, backing_width, backing_height,
>> -                         backing_id, false);
>> +        gtk_egl_set_scanout_mode(vc, true);
>> +        egl_fb_setup_for_tex(&vc->gfx.guest_fb, backing_width, 
>> backing_height,
>> +                             backing_id, false);
>> +    }
>>  }
>>  
>>  void gd_egl_scanout_dmabuf(DisplayChangeListener *dcl,

I can see the mistake. I'll write a patch to fix it.

With best regards,
Volker