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,