Implement NFC filters for Ambisonic rendering

NFC filters currently only work when rendering to ambisonic buffers, which
includes HQ rendering and ambisonic output. There are two new config options:
'decoder/nfc' (default on) enables or disables use of NFC filters globally, and
'decoder/nfc-ref-delay' (default 0) specifies the reference delay parameter for
NFC-HOA rendering with ambisonic output (a value of 0 disables NFC).

Currently, NFC filters rely on having an appropriate value set for
AL_METERS_PER_UNIT to get the correct scaling. HQ rendering uses the averaged
speaker distances as a control/reference, and currently doesn't correct for
individual speaker distances (if the speakers are all equidistant, this is
fine, otherwise per-speaker correction should be done as well).

1 files changed, 20 insertions, 0 deletions

diff --git a/Alc/ALc.c b/Alc/ALc.c
index 882a8cb0..beec0c32 100644
--- a/Alc/ALc.c
+++ b/Alc/ALc.c
@@ -2310,6 +2310,24 @@ static ALCenum UpdateDeviceParams(ALCdevice *device, const ALCint *attrList)
             }
         }
         AllocateVoices(context, context->MaxVoices, old_sends);
+        for(pos = 0;pos < context->VoiceCount;pos++)
+        {
+            ALvoice *voice = context->Voices[pos];
+            if(!voice->Source) continue;
+
+            if(device->AvgSpeakerDist > 0.0f)
+            {
+                /* Reinitialize the NFC filters for new parameters. */
+                ALfloat w1 = SPEEDOFSOUNDMETRESPERSEC /
+                             (device->AvgSpeakerDist * device->Frequency);
+                for(i = 0;i < voice->NumChannels;i++)
+                {
+                    NfcFilterCreate1(&voice->Direct.Params[i].NFCtrlFilter[0], 0.0f, w1);
+                    NfcFilterCreate2(&voice->Direct.Params[i].NFCtrlFilter[1], 0.0f, w1);
+                    NfcFilterCreate3(&voice->Direct.Params[i].NFCtrlFilter[2], 0.0f, w1);
+                }
+            }
+        }
         UnlockUIntMapRead(&context->SourceMap);
 
         UpdateListenerProps(context);
@@ -3755,6 +3773,7 @@ ALC_API ALCdevice* ALC_APIENTRY alcOpenDevice(const ALCchar *deviceName)
     device->FOAOut.NumChannels = 0;
     device->RealOut.Buffer = NULL;
     device->RealOut.NumChannels = 0;
+    device->AvgSpeakerDist = 0.0f;
 
     ATOMIC_INIT(&device->ContextList, NULL);
 
@@ -4271,6 +4290,7 @@ ALC_API ALCdevice* ALC_APIENTRY alcLoopbackOpenDeviceSOFT(const ALCchar *deviceN
     device->FOAOut.NumChannels = 0;
     device->RealOut.Buffer = NULL;
     device->RealOut.NumChannels = 0;
+    device->AvgSpeakerDist = 0.0f;
 
     ATOMIC_INIT(&device->ContextList, NULL);