dsound: Support downmixing 5.1 to stereo.

dlls/dsound/dsound_convert.c

@@ -157,6 +157,13 @@ void putieee32(const IDirectSoundBufferImpl *dsb, DWORD pos, DWORD channel, floa
     *fbuf = value;
 }
 
+void putieee32_sum(const IDirectSoundBufferImpl *dsb, DWORD pos, DWORD channel, float value)
+{
+    BYTE *buf = (BYTE *)dsb->device->tmp_buffer;
+    float *fbuf = (float*)(buf + pos + sizeof(float) * channel);
+    *fbuf += value;
+}
+
 void put_mono2stereo(const IDirectSoundBufferImpl *dsb, DWORD pos, DWORD channel, float value)
 {
     dsb->put_aux(dsb, pos, 0, value);
@@ -206,6 +213,45 @@ void put_stereo2surround51(const IDirectSoundBufferImpl *dsb, DWORD pos, DWORD c
     }
 }
 
+void put_surround512stereo(const IDirectSoundBufferImpl *dsb, DWORD pos, DWORD channel, float value)
+{
+    /* based on pulseaudio's downmix algorithm */
+    switch(channel){
+
+    case 4: /* back left */
+        value *= 0.056f; /* (1/9) / (sum of left volumes) */
+        dsb->put_aux(dsb, pos, 0, value);
+        break;
+
+    case 0: /* front left */
+        value *= 0.503; /* 1 / (sum of left volumes) */
+        dsb->put_aux(dsb, pos, 0, value);
+        break;
+
+    case 5: /* back right */
+        value *= 0.056f; /* (1/9) / (sum of right volumes) */
+        dsb->put_aux(dsb, pos, 1, value);
+        break;
+
+    case 1: /* front right */
+        value *= 0.503f; /* 1 / (sum of right volumes) */
+        dsb->put_aux(dsb, pos, 1, value);
+        break;
+
+    case 2: /* front centre */
+        value *= 0.252f; /* 0.5 / (sum of left/right volumes) */
+        dsb->put_aux(dsb, pos, 0, value);
+        dsb->put_aux(dsb, pos, 1, value);
+        break;
+
+    case 3: /* LFE */
+        value *= 0.189f; /* 0.375 / (sum of left/right volumes) */
+        dsb->put_aux(dsb, pos, 0, value);
+        dsb->put_aux(dsb, pos, 1, value);
+        break;
+    }
+}
+
 void mixieee32(float *src, float *dst, unsigned samples)
 {
     TRACE("%p - %p %d\n", src, dst, samples);

dlls/dsound/dsound_private.h

@@ -47,6 +47,7 @@ typedef float (*bitsgetfunc)(const IDirectSoundBufferImpl *, DWORD, DWORD);
 typedef void (*bitsputfunc)(const IDirectSoundBufferImpl *, DWORD, DWORD, float);
 extern const bitsgetfunc getbpp[5] DECLSPEC_HIDDEN;
 void putieee32(const IDirectSoundBufferImpl *dsb, DWORD pos, DWORD channel, float value) DECLSPEC_HIDDEN;
+void putieee32_sum(const IDirectSoundBufferImpl *dsb, DWORD pos, DWORD channel, float value) DECLSPEC_HIDDEN;
 void mixieee32(float *src, float *dst, unsigned samples) DECLSPEC_HIDDEN;
 typedef void (*normfunc)(const void *, void *, unsigned);
 extern const normfunc normfunctions[4] DECLSPEC_HIDDEN;
@@ -177,6 +178,7 @@ void put_mono2quad(const IDirectSoundBufferImpl *dsb, DWORD pos, DWORD channel,
 void put_stereo2quad(const IDirectSoundBufferImpl *dsb, DWORD pos, DWORD channel, float value) DECLSPEC_HIDDEN;
 void put_mono2surround51(const IDirectSoundBufferImpl *dsb, DWORD pos, DWORD channel, float value) DECLSPEC_HIDDEN;
 void put_stereo2surround51(const IDirectSoundBufferImpl *dsb, DWORD pos, DWORD channel, float value) DECLSPEC_HIDDEN;
+void put_surround512stereo(const IDirectSoundBufferImpl *dsb, DWORD pos, DWORD channel, float value) DECLSPEC_HIDDEN;
 
 HRESULT secondarybuffer_create(DirectSoundDevice *device, const DSBUFFERDESC *dsbd,
         IDirectSoundBuffer **buffer) DECLSPEC_HIDDEN;

dlls/dsound/mixer.c

@@ -173,6 +173,12 @@ void DSOUND_RecalcFormat(IDirectSoundBufferImpl *dsb)
 		dsb->mix_channels = 2;
 		dsb->put = put_stereo2surround51;
 	}
+	else if (ichannels == 6 && ochannels == 2)
+	{
+		dsb->mix_channels = 6;
+		dsb->put = put_surround512stereo;
+		dsb->put_aux = putieee32_sum;
+	}
 	else
 	{
 		if (ichannels > 2)
@@ -495,6 +501,8 @@ static DWORD DSOUND_MixInBuffer(IDirectSoundBufferImpl *dsb, float *mix_buffer,
 	/* Resample buffer to temporary buffer specifically allocated for this purpose, if needed */
 	oldpos = dsb->sec_mixpos;
 
+	if(dsb->put_aux == putieee32_sum)
+		memset(dsb->device->tmp_buffer, 0, dsb->device->tmp_buffer_len);
 	DSOUND_MixToTemporary(dsb, frames);
 	ibuf = dsb->device->tmp_buffer;