[vlc-commits] DirectSound: possibly fix volume computation

[Rémi Denis-Courmont]

vlc | branch: master | Rémi Denis-Courmont <remi at remlab.net> | Wed May 30 22:03:59 2012 +0300| [a4e7d80196972f8f236219d51e2777c86fcb6aeb] | committer: Rémi Denis-Courmont

DirectSound: possibly fix volume computation

It seems the volume is expected to be negative. At least, WinCE MSDN
and MingW and the Internets say so. Windows MSDN says the opposite...

> http://git.videolan.org/gitweb.cgi/vlc.git/?a=commit;h=a4e7d80196972f8f236219d51e2777c86fcb6aeb
---

 modules/audio_output/directx.c |   29 ++++++++++++++---------------
 1 file changed, 14 insertions(+), 15 deletions(-)

diff --git a/modules/audio_output/directx.c b/modules/audio_output/directx.c
index 6069c24..97df5ff 100644
--- a/modules/audio_output/directx.c
+++ b/modules/audio_output/directx.c
@@ -580,25 +580,24 @@ static void Play( audio_output_t *p_aout, block_t *p_buffer )
 static int VolumeSet( audio_output_t *p_aout, float vol, bool mute )
 {
     aout_sys_t *sys = p_aout->sys;
-    LONG volume;
-    float f = vol;
 
-    if( mute )
-        f = 0.;
-    /* Convert UI volume percentage to linear factor (cube) */
-    f = f * f * f;
-
-    /* "DirectSound does not support amplification." -- MSDN */
-    if( f > 1. )
-        f = 1.;
+    /* Convert UI volume to linear factor (cube) */
+    vol = vol * vol * vol;
 
     /* millibels from linear amplification */
-    if( f <= powf(10., DSBVOLUME_MIN / -2000.) )
-        volume = DSBVOLUME_MIN;
-    else
-        volume = lroundf(-2000. * log10f(f));
+    LONG mb = lroundf(2000.f * log10f(vol));
+
+    /* Clamp to allowed DirectSound range */
+    static_assert( DSBVOLUME_MIN < DSBVOLUME_MAX, "DSBVOLUME_* confused" );
+    if( mb >= DSBVOLUME_MAX )
+        mb = DSBVOLUME_MAX;
+    if( mb <= DSBVOLUME_MIN )
+        mb = DSBVOLUME_MIN;
+
+    InterlockedExchange(&sys->volume, mute ? DSBVOLUME_MIN : mb);
 
-    InterlockedExchange(&sys->volume, volume);
+    /* Convert back to UI volume */
+    vol = cbrtf(powf(10.f, ((float)mb) / -2000.f));
     aout_VolumeHardSet( p_aout, vol, mute );
     return 0;
 }