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, 7 insertions, 0 deletions

diff --git a/OpenAL32/Include/alMain.h b/OpenAL32/Include/alMain.h
index cc30dcef..e4c5b94a 100644
--- a/OpenAL32/Include/alMain.h
+++ b/OpenAL32/Include/alMain.h
@@ -726,6 +726,7 @@ struct ALCdevice_struct
     alignas(16) ALfloat SourceData[BUFFERSIZE];
     alignas(16) ALfloat ResampledData[BUFFERSIZE];
     alignas(16) ALfloat FilteredData[BUFFERSIZE];
+    alignas(16) ALfloat NFCtrlData[BUFFERSIZE];
 
     /* The "dry" path corresponds to the main output. */
     struct {
@@ -738,6 +739,7 @@ struct ALCdevice_struct
 
         ALfloat (*Buffer)[BUFFERSIZE];
         ALsizei NumChannels;
+        ALsizei NumChannelsPerOrder[MAX_AMBI_ORDER+1];
     } Dry;
 
     /* First-order ambisonics output, to be upsampled to the dry buffer if different. */
@@ -760,6 +762,11 @@ struct ALCdevice_struct
         ALsizei NumChannels;
     } RealOut;
 
+    /* The average speaker distance as determined by the ambdec configuration
+     * (or alternatively, by the NFC-HOA reference delay). Only used for NFC.
+     */
+    ALfloat AvgSpeakerDist;
+
     /* Delay buffers used to compensate for speaker distances. */
     DistanceComp ChannelDelay[MAX_OUTPUT_CHANNELS];