dsoundaudio: replace GetForegroundWindow()

GetForegroundWindow() doesn't necessarily return the own window
handle. It just returns a handle to the currently active window
and can even return NULL. At the time dsound_open() gets called
the active window is most likely the shell window and not the
QEMU window.

Replace GetForegroundWindow() with GetDesktopWindow() which
always returns a valid window handle, and at the same time
replace the DirectSound buffer flag DSBCAPS_STICKYFOCUS with
DSBCAPS_GLOBALFOCUS where Windows only expects a valid window
handle for DirectSound function SetCooperativeLevel(). The
Microsoft online docs for IDirectSound::SetCooperativeLevel
recommend this in the remarks.

This fixes a bug where you can't hear sound from the guest.

To reproduce start qemu with -machine pcspk-audiodev=audio0
-device intel-hda -device hda-duplex,audiodev=audio0
-audiodev dsound,id=audio0,out.mixing-engine=off
from a shell and start audio playback with the hda device in the
guest. The guest will be silent. To hear guest audio you have to
activate the shell window once.

Signed-off-by: Volker Rümelin <vr_qemu@t-online.de>
Message-id: 9315afe5-5958-c0b4-ea1e-14769511a9d5@t-online.de
Message-Id: <20210110100239.27588-20-vr_qemu@t-online.de>
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>

audio/dsound_template.h

@@ -205,7 +205,7 @@ static int dsound_init_out(HWVoiceOut *hw, struct audsettings *as,
         NULL
         );
 #else
-    bd.dwFlags = DSBCAPS_STICKYFOCUS | DSBCAPS_GETCURRENTPOSITION2;
+    bd.dwFlags = DSBCAPS_GLOBALFOCUS | DSBCAPS_GETCURRENTPOSITION2;
     hr = IDirectSound_CreateSoundBuffer (
         s->dsound,
         &bd,

audio/dsoundaudio.c

@@ -347,7 +347,7 @@ static int dsound_open (dsound *s)
     HRESULT hr;
     HWND hwnd;
 
-    hwnd = GetForegroundWindow ();
+    hwnd = GetDesktopWindow();
     hr = IDirectSound_SetCooperativeLevel (
         s->dsound,
         hwnd,