Re: [PATCH 0/3] SDL2 usability fixes

[Volker Rümelin]

> Am
>       13.04.23 um 22:43 schrieb Bernhard Beschow: 
> >  
> >         Am 13. April 2023 17:54:34 UTC schrieb "Volker Rümelin" <vr_qemu@t-online.de>:
> >         
> > > > I'm trying to use QEMU on Windows
> > > >             hosts for fun and for profit. While the GTK 
> > > >             GUI doesn't seem to support OpenGL under Windows the SDL2
> > > >             GUI does. Hence I 
> > > >             used the SDL2 GUI where I ran into several issues of which
> > > >             three are fixed in 
> > > >             this series, which are: 
> > > >             
> > > >             * Alt+Tab switches tasks on the host rather than in the
> > > >             guest in fullscreen mode 
> > > >             * Alt+F4 closes QEMU rather than a graphical task in the
> > > >             guest 
> > > >             * AltGr keyboard modifier isn't recognized by a Linux guest
> > > >             
> > > >             
> > > >             More information about each issue is provided in the
> > > >             patches. 
> > > >             
> > > >             Bernhard Beschow (3): 
> > > >                 ui/sdl2: Grab Alt+Tab also in fullscreen mode 
> > > >                 ui/sdl2: Grab Alt+F4 also under Windows 
> > > >                 ui/sdl2-input: Fix AltGr modifier on Windows hosts 
> > > >             
> > > >                ui/sdl2-input.c | 13 +++++++++++++ 
> > > >                ui/sdl2.c       |  2 ++ 
> > > >                2 files changed, 15 insertions(+) 
> > > >             
> > > >           
> > >           Hi Bernhard, 
> > >         
> >         Hi Volker, 
> >         
> > > I don't think these patches are
> > >           necessary. The AltGr key and the keyboard grab was fixed in
> > >           2020 with commit 830473455f ("ui/sdl2: fix handling of AltGr
> > >           key on Windows") and a few commits before. 
> > >         
> >         Indeed, this patch addresses the AltGr issue. What I noticed in
> >         my case is that the AltGr behavior is different, depending on
> >         whether the *guest* is in graphics mode or not. Pressing AltGr
> >         in graphics mode issues two key modifiers while only one is
> >         issued when the guest is in text mode. I'll recheck tomorrow
> >         when I have access to a Windows host. 
> >       
>       
>       Hi Bernhard, 
>       
>       the AltGr behavior depends on the keyboard grab. The AltGr key
>       works without keyboard grabbed and it doesn't with keyboard
>       grabbed. That's a bug. 
>     
    
    Hi Bernhard,
    
    this used to work before SDL2-2.0.16. There was no code for Windows
    in SDL2 to handle keyboard grabs. Version 2.0.16 introduced a
    Windows low level keyboard hook procedure to grab the keyboard.
    Windows calls this callback before the QEMU keyboard hook procedure.
    This explains the observed behavior.
    
    The fix is to disable SDL_SetHint(SDL_HINT_GRAB_KEYBOARD, "1"); for
    Windows. This restores the QEMU keyboard grab for all Windows SDL2
    versions. Your first two patches are also necessary. But I think you
    will need a #ifdef SDL_HINT_ALLOW_ALT_TAB_WHILE_GRABBED
    for older SDL2 versions.
    
    I'll write a patch similar to this one after more tests.
    
diff --git a/ui/sdl2.c b/ui/sdl2.c
index b011e8d759..9f6b959464 100644
--- a/ui/sdl2.c
+++ b/ui/sdl2.c
@@ -855,7 +855,9 @@ static void sdl2_display_init(DisplayState *ds, DisplayOptions *o)
 #ifdef SDL_HINT_VIDEO_X11_NET_WM_BYPASS_COMPOSITOR /* only available since SDL 2.0.8 */
     SDL_SetHint(SDL_HINT_VIDEO_X11_NET_WM_BYPASS_COMPOSITOR, "0");
 #endif
+#ifndef CONFIG_WIN32
     SDL_SetHint(SDL_HINT_GRAB_KEYBOARD, "1");
+#endif
 #ifdef SDL_HINT_ALLOW_ALT_TAB_WHILE_GRABBED
     /* available since SDL 2.0.16 */
     SDL_SetHint(SDL_HINT_ALLOW_ALT_TAB_WHILE_GRABBED, "0");
-- 
2.35.3

    With best regards,
    Volker
    
>  
> >  
> >         What about the other two issues? My other two patches override
> >         SDL2 defaults which aren't addressed yet in QEMU AFAICS. The
> >         Alt+Tab one isn't even Windows-specific. 
> >         
> > > Something broke in the last few weeks.
> > >           At the moment my Linux guest fails to start on Windows with
> > >           -display sdl. QEMU locks up a short time after the Linux
> > >           kernel starts. 
> > >         
> >         This doesn't happen for me with 8.0rc4 and latest msys2
> >         environment. I'm running with `-accel whpx -vga none -device
> >         virtio-vga-gl -display sdl,gl=on` and I even get decent OpenGL
> >         accelleration when the Linux guest is in graphics mode, with
> >         wobbly windows etc. Sometimes QEMU aborts when it can't map some
> >         OpenGL stuff when the guest enters graphics mode but once that
> >         succeeds it runs absolutely stable. 
> >         
> > > I'll try to find the commit that caused
> > >           this regression. 
> > >         
> >       
>       
>       I tested with QEMU 7.1 and sometimes it also locks up. This
>       indicates that the QEMU code doesn't have an issue. 
>       
>       With best regards, 
>       Volker 
>       
> > Yes, this would be interesting. 
> >         
> >         Best regards, 
> >         Bernhard 
> >         
> > > With best regards, 
> > >           Volker 
> > >         
> >       
>       
>