Remix missing channels with direct channels enabled

Instead of dropping them.

3 files changed, 83 insertions, 6 deletions

diff --git a/alc/alc.cpp b/alc/alc.cpp
index 06f8ce59..9c4dbcbd 100644
--- a/alc/alc.cpp
+++ b/alc/alc.cpp
@@ -1308,8 +1308,10 @@ ALuint ChannelsFromDevFmt(DevFmtChannels chans, ALuint ambiorder) noexcept
     return 0;
 }
 
+namespace {
+
 struct DevFmtPair { DevFmtChannels chans; DevFmtType type; };
-static al::optional<DevFmtPair> DecomposeDevFormat(ALenum format)
+al::optional<DevFmtPair> DecomposeDevFormat(ALenum format)
 {
     static const struct {
         ALenum format;
@@ -1350,7 +1352,7 @@ static al::optional<DevFmtPair> DecomposeDevFormat(ALenum format)
     return al::nullopt;
 }
 
-static ALCboolean IsValidALCType(ALCenum type)
+ALCboolean IsValidALCType(ALCenum type)
 {
     switch(type)
     {
@@ -1366,7 +1368,7 @@ static ALCboolean IsValidALCType(ALCenum type)
     return ALC_FALSE;
 }
 
-static ALCboolean IsValidALCChannels(ALCenum channels)
+ALCboolean IsValidALCChannels(ALCenum channels)
 {
     switch(channels)
     {
@@ -1382,7 +1384,7 @@ static ALCboolean IsValidALCChannels(ALCenum channels)
     return ALC_FALSE;
 }
 
-static ALCboolean IsValidAmbiLayout(ALCenum layout)
+ALCboolean IsValidAmbiLayout(ALCenum layout)
 {
     switch(layout)
     {
@@ -1393,7 +1395,7 @@ static ALCboolean IsValidAmbiLayout(ALCenum layout)
     return ALC_FALSE;
 }
 
-static ALCboolean IsValidAmbiScaling(ALCenum scaling)
+ALCboolean IsValidAmbiScaling(ALCenum scaling)
 {
     switch(scaling)
     {
@@ -1405,6 +1407,45 @@ static ALCboolean IsValidAmbiScaling(ALCenum scaling)
     return ALC_FALSE;
 }
 
+
+/* Downmixing channel arrays, to map the given format's missing channels to
+ * existing ones. Based on Wine's DSound downmix values, which are based on
+ * PulseAudio's.
+ */
+const std::array<InputRemixMap,6> StereoDownmix{{
+    { FrontCenter, {{{FrontLeft, 0.5f},      {FrontRight, 0.5f}}} },
+    { SideLeft,    {{{FrontLeft, 1.0f/9.0f}, {FrontRight, 0.0f}}} },
+    { SideRight,   {{{FrontLeft, 0.0f},      {FrontRight, 1.0f/9.0f}}} },
+    { BackLeft,    {{{FrontLeft, 1.0f/9.0f}, {FrontRight, 0.0f}}} },
+    { BackRight,   {{{FrontLeft, 0.0f},      {FrontRight, 1.0f/9.0f}}} },
+    { BackCenter,  {{{FrontLeft, 0.5f/9.0f}, {FrontRight, 0.5f/9.0f}}} },
+}};
+const std::array<InputRemixMap,4> QuadDownmix{{
+    { FrontCenter, {{{FrontLeft,  0.5f}, {FrontRight, 0.5f}}} },
+    { SideLeft,    {{{FrontLeft,  0.5f}, {BackLeft,   0.5f}}} },
+    { SideRight,   {{{FrontRight, 0.5f}, {BackRight,  0.5f}}} },
+    { BackCenter,  {{{BackLeft,   0.5f}, {BackRight,  0.5f}}} },
+}};
+const std::array<InputRemixMap,3> X51Downmix{{
+    { BackLeft,   {{{SideLeft, 1.0f}, {SideRight, 0.0f}}} },
+    { BackRight,  {{{SideLeft, 0.0f}, {SideRight, 1.0f}}} },
+    { BackCenter, {{{SideLeft, 0.5f}, {SideRight, 0.5f}}} },
+}};
+const std::array<InputRemixMap,3> X51RearDownmix{{
+    { SideLeft,   {{{BackLeft, 1.0f}, {BackRight, 0.0f}}} },
+    { SideRight,  {{{BackLeft, 0.0f}, {BackRight, 1.0f}}} },
+    { BackCenter, {{{BackLeft, 0.5f}, {BackRight, 0.5f}}} },
+}};
+const std::array<InputRemixMap,2> X61Downmix{{
+    { BackLeft,  {{{BackCenter, 0.5f}, {SideLeft,  0.5f}}} },
+    { BackRight, {{{BackCenter, 0.5f}, {SideRight, 0.5f}}} },
+}};
+const std::array<InputRemixMap,1> X71Downmix{{
+    { BackCenter, {{{BackLeft, 0.5f}, {BackRight, 0.5f}}} },
+}};
+
+} // namespace
+
 /************************************************
  * Miscellaneous ALC helpers
  ************************************************/
@@ -1859,6 +1900,7 @@ static ALCenum UpdateDeviceParams(ALCdevice *device, const ALCint *attrList)
     device->Dry.AmbiMap.fill(BFChannelConfig{});
     device->Dry.Buffer = {};
     std::fill(std::begin(device->NumChannelsPerOrder), std::end(device->NumChannelsPerOrder), 0u);
+    device->RealOut.RemixMap = {};
     device->RealOut.ChannelIndex.fill(INVALID_CHANNEL_INDEX);
     device->RealOut.Buffer = {};
     device->MixBuffer.clear();
@@ -1935,6 +1977,18 @@ static ALCenum UpdateDeviceParams(ALCdevice *device, const ALCint *attrList)
         DevFmtChannelsString(device->FmtChans), DevFmtTypeString(device->FmtType),
         device->Frequency, device->UpdateSize, device->BufferSize);
 
+    switch(device->FmtChans)
+    {
+    case DevFmtStereo: device->RealOut.RemixMap = StereoDownmix; break;
+    case DevFmtQuad: device->RealOut.RemixMap = QuadDownmix; break;
+    case DevFmtX51: device->RealOut.RemixMap = X51Downmix; break;
+    case DevFmtX51Rear: device->RealOut.RemixMap = X51RearDownmix; break;
+    case DevFmtX61: device->RealOut.RemixMap = X61Downmix; break;
+    case DevFmtX71: device->RealOut.RemixMap = X71Downmix; break;
+    case DevFmtMono:
+    case DevFmtAmbi3D: break;
+    }
+
     aluInitRenderer(device, hrtf_id, hrtf_appreq, hrtf_userreq);
 
     device->NumAuxSends = new_sends;
diff --git a/alc/alcmain.h b/alc/alcmain.h
index 1da332c0..673997dc 100644
--- a/alc/alcmain.h
+++ b/alc/alcmain.h
@@ -60,6 +60,14 @@ enum RenderMode {
 };
 
 
+struct InputRemixMap {
+    struct TargetMix { Channel channel; float mix; };
+
+    Channel channel;
+    std::array<TargetMix,2> targets;
+};
+
+
 struct BufferSubList {
     uint64_t FreeMask{~0_u64};
     ALbuffer *Buffers{nullptr}; /* 64 */
@@ -184,6 +192,7 @@ struct MixParams {
 };
 
 struct RealMixParams {
+    al::span<const InputRemixMap> RemixMap;
     std::array<ALuint,MaxChannels> ChannelIndex{};
 
     al::span<FloatBufferLine> Buffer;
diff --git a/alc/alu.cpp b/alc/alu.cpp
index f228ff29..deb0bb54 100644
--- a/alc/alu.cpp
+++ b/alc/alu.cpp
@@ -942,9 +942,23 @@ void CalcPanningAndFilters(ALvoice *voice, const ALfloat xpos, const ALfloat ypo
 
         for(ALuint c{0};c < num_channels;c++)
         {
-            const ALuint idx{GetChannelIdxByName(Device->RealOut, chans[c].channel)};
+            ALuint idx{GetChannelIdxByName(Device->RealOut, chans[c].channel)};
             if(idx != INVALID_CHANNEL_INDEX)
                 voice->mChans[c].mDryParams.Gains.Target[idx] = DryGain;
+            else
+            {
+                auto match_channel = [chans,c](const InputRemixMap &map) -> bool
+                { return chans[c].channel == map.channel; };
+                auto remap = std::find_if(Device->RealOut.RemixMap.cbegin(),
+                    Device->RealOut.RemixMap.cend(), match_channel);
+                if(remap != Device->RealOut.RemixMap.cend())
+                    for(const auto &target : remap->targets)
+                    {
+                        idx = GetChannelIdxByName(Device->RealOut, target.channel);
+                        if(idx != INVALID_CHANNEL_INDEX)
+                            voice->mChans[c].mDryParams.Gains.Target[idx] = target.mix;
+                    }
+            }
         }
 
         /* Auxiliary sends still use normal channel panning since they mix to