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Add a comment detailing how the HRTF channel buffer is set up

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This commit is contained in:
Chris Robinson
2015-02-09 08:11:07 -08:00
parent a925fb8111
commit 1393af4f9f
1 changed files with 45 additions and 19 deletions
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Alc/ALu.c
+45 -19
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@@ -93,6 +93,27 @@ extern inline void aluMatrixSet(aluMatrix *restrict matrix, ALfloat m00, ALfloat
ALfloat m20, ALfloat m21, ALfloat m22, ALfloat m23,
ALfloat m30, ALfloat m31, ALfloat m32, ALfloat m33);
/* NOTE: HRTF is set up a bit special in the device. By default, the device's
* DryBuffer, NumChannels, ChannelName, and Channel fields correspond to the
* output mixing format, and the DryBuffer is then converted and written to the
* backend's audio buffer.
*
* With HRTF, these fields correspond to a virtual format (typically 8-channel
* cube), and the actual output is stored in DryBuffer[NumChannels] for the
* left channel and DryBuffer[NumChannels+1] for the right. As a final output
* step, the virtual channels will have HRTF applied and written to the actual
* output. Things like effects and B-Format decoding will want to write to the
* virtual channels so that they can be mixed with HRTF in full 3D.
*
* Sources that get mixed using HRTF directly will need to offset the output
* buffer so that they skip the virtual output and write to the actual output
* channels. This is the reason you'll see
*
* voice->Direct.OutBuffer += voice->Direct.OutChannels;
* voice->Direct.OutChannels = 2;
*
* at various points in the code where HRTF is explicitly used or bypassed.
*/
static inline HrtfMixerFunc SelectHrtfMixer(void)
{
@@ -1176,24 +1197,29 @@ ALvoid aluMixData(ALCdevice *device, ALvoid *buffer, ALsizei size)
while(size > 0)
{
ALuint outchanoffset = 0;
ALuint outchancount = device->NumChannels;
ALfloat (*OutBuffer)[BUFFERSIZE];
ALuint OutChannels;
IncrementRef(&device->MixCount);
OutBuffer = device->DryBuffer;
OutChannels = device->NumChannels;
SamplesToDo = minu(size, BUFFERSIZE);
for(c = 0;c < device->NumChannels;c++)
memset(device->DryBuffer[c], 0, SamplesToDo*sizeof(ALfloat));
for(c = 0;c < OutChannels;c++)
memset(OutBuffer[c], 0, SamplesToDo*sizeof(ALfloat));
if(device->Hrtf)
{
outchanoffset = device->NumChannels;
outchancount = 2;
for(c = 0;c < outchancount;c++)
memset(device->DryBuffer[outchanoffset+c], 0, SamplesToDo*sizeof(ALfloat));
/* Set OutBuffer/OutChannels to correspond to the actual output
* with HRTF. Make sure to clear them too. */
OutBuffer += OutChannels;
OutChannels = 2;
for(c = 0;c < OutChannels;c++)
memset(OutBuffer[c], 0, SamplesToDo*sizeof(ALfloat));
}
V0(device->Backend,lock)();
V(device->Synth,process)(SamplesToDo, &device->DryBuffer[outchanoffset]);
V(device->Synth,process)(SamplesToDo, OutBuffer);
ctx = ATOMIC_LOAD(&device->ContextList);
while(ctx)
@@ -1278,9 +1304,9 @@ ALvoid aluMixData(ALCdevice *device, ALvoid *buffer, ALsizei size)
HrtfMixerFunc HrtfMix = SelectHrtfMixer();
ALuint irsize = GetHrtfIrSize(device->Hrtf);
for(c = 0;c < device->NumChannels;c++)
HrtfMix(&device->DryBuffer[outchanoffset], device->DryBuffer[c], 0,
device->Hrtf_Offset, 0, irsize, &device->Hrtf_Params[c],
&device->Hrtf_State[c], SamplesToDo
HrtfMix(OutBuffer, device->DryBuffer[c], 0, device->Hrtf_Offset,
0, irsize, &device->Hrtf_Params[c], &device->Hrtf_State[c],
SamplesToDo
);
device->Hrtf_Offset += SamplesToDo;
}
@@ -1307,25 +1333,25 @@ ALvoid aluMixData(ALCdevice *device, ALvoid *buffer, ALsizei size)
switch(device->FmtType)
{
case DevFmtByte:
WRITE(ALbyte, device->DryBuffer+outchanoffset, buffer, SamplesToDo, outchancount);
WRITE(ALbyte, OutBuffer, buffer, SamplesToDo, OutChannels);
break;
case DevFmtUByte:
WRITE(ALubyte, device->DryBuffer+outchanoffset, buffer, SamplesToDo, outchancount);
WRITE(ALubyte, OutBuffer, buffer, SamplesToDo, OutChannels);
break;
case DevFmtShort:
WRITE(ALshort, device->DryBuffer+outchanoffset, buffer, SamplesToDo, outchancount);
WRITE(ALshort, OutBuffer, buffer, SamplesToDo, OutChannels);
break;
case DevFmtUShort:
WRITE(ALushort, device->DryBuffer+outchanoffset, buffer, SamplesToDo, outchancount);
WRITE(ALushort, OutBuffer, buffer, SamplesToDo, OutChannels);
break;
case DevFmtInt:
WRITE(ALint, device->DryBuffer+outchanoffset, buffer, SamplesToDo, outchancount);
WRITE(ALint, OutBuffer, buffer, SamplesToDo, OutChannels);
break;
case DevFmtUInt:
WRITE(ALuint, device->DryBuffer+outchanoffset, buffer, SamplesToDo, outchancount);
WRITE(ALuint, OutBuffer, buffer, SamplesToDo, OutChannels);
break;
case DevFmtFloat:
WRITE(ALfloat, device->DryBuffer+outchanoffset, buffer, SamplesToDo, outchancount);
WRITE(ALfloat, OutBuffer, buffer, SamplesToDo, OutChannels);
break;
}
#undef WRITE