Support concatenated spatialization data

Source/core/platform/audio/HRTFElevation.cpp

Index: Source/core/platform/audio/HRTFElevation.cpp
diff --git a/Source/core/platform/audio/HRTFElevation.cpp b/Source/core/platform/audio/HRTFElevation.cpp
index 9bf6e5f742f48f51016249e5091de74fcdeca20f..e7092ec9927e8ea64a6a321f7ab07225dddd1d5c 100644
--- a/Source/core/platform/audio/HRTFElevation.cpp
+++ b/Source/core/platform/audio/HRTFElevation.cpp
@@ -62,6 +62,40 @@ const size_t ResponseFrameSize = 256;
 // The impulse responses may be resampled to a different sample-rate (depending on the audio hardware) when they are loaded.
 const float ResponseSampleRate = 44100;
 
+#if USE(CONCATENATED_IMPULSE_RESPONSES)
+// Lazily load a concatenated HRTF database for given subject and store it in a
+// local hash table to ensure quick efficient future retrievals.
+static PassRefPtr<AudioBus> getConcatenatedImpulseResponsesForSubject(const String& subjectName)
+{
+    typedef HashMap<String, RefPtr<AudioBus> > AudioBusMap;
+    DEFINE_STATIC_LOCAL(AudioBusMap, audioBusMap, ());
+
+    RefPtr<AudioBus> bus;
+    AudioBusMap::iterator iterator = audioBusMap.find(subjectName);
+    if (iterator == audioBusMap.end()) {
+        RefPtr<AudioBus> concatenatedImpulseResponses(AudioBus::loadPlatformResource(subjectName.utf8().data(), ResponseSampleRate));
+        ASSERT(concatenatedImpulseResponses);
+        if (!concatenatedImpulseResponses)
+            return 0;
+
+        bus = concatenatedImpulseResponses;
+        audioBusMap.set(subjectName, bus);
+    } else
+        bus = iterator->value;
+
+    size_t responseLength = bus->length();
+    size_t expectedLength = static_cast<size_t>(TotalNumberOfResponses * ResponseFrameSize);
+
+    // Check number of channels and length. For now these are fixed and known.
+    bool isBusGood = responseLength == expectedLength && bus->numberOfChannels() == 2;
+    ASSERT(isBusGood);
+    if (!isBusGood)
+        return 0;
+
+    return bus;
+}
+#endif
+
 // Takes advantage of the symmetry and creates a composite version of the two measured versions.  For example, we have both azimuth 30 and -30 degrees
 // where the roles of left and right ears are reversed with respect to each other.
 bool HRTFElevation::calculateSymmetricKernelsForAzimuthElevation(int azimuth, int elevation, float sampleRate, const String& subjectName,
@@ -111,6 +145,36 @@ bool HRTFElevation::calculateKernelsForAzimuthElevation(int azimuth, int elevati
     // It's passed in as an internal ASCII identifier and is an implementation detail.
     int positiveElevation = elevation < 0 ? elevation + 360 : elevation;
 
+#if USE(CONCATENATED_IMPULSE_RESPONSES)
+    RefPtr<AudioBus> bus(getConcatenatedImpulseResponsesForSubject(subjectName));
+
+    if (!bus)
+        return false;
+
+    int elevationIndex = positiveElevation / AzimuthSpacing;
+    if (positiveElevation > 90)
+        elevationIndex -= AzimuthSpacing;
+
+    // The concatenated impulse response is a bus containing all
+    // the elevations per azimuth, for all azimuths by increasing
+    // order. So for a given azimuth and elevation we need to compute
+    // the index of the wanted audio frames in the concatenated table.
+    unsigned index = ((azimuth / AzimuthSpacing) * HRTFDatabase::NumberOfRawElevations) + elevationIndex;
+    bool isIndexGood = index < TotalNumberOfResponses;
+    ASSERT(isIndexGood);
+    if (!isIndexGood)
+        return false;
+
+    // Extract the individual impulse response from the concatenated
+    // responses and potentially sample-rate convert it to the desired
+    // (hardware) sample-rate.
+    unsigned startFrame = index * ResponseFrameSize;
+    unsigned stopFrame = startFrame + ResponseFrameSize;
+    RefPtr<AudioBus> preSampleRateConvertedResponse(AudioBus::createBufferFromRange(bus.get(), startFrame, stopFrame));
+    RefPtr<AudioBus> response(AudioBus::createBySampleRateConverting(preSampleRateConvertedResponse.get(), false, sampleRate));
+    AudioChannel* leftEarImpulseResponse = response->channel(AudioBus::ChannelLeft);
+    AudioChannel* rightEarImpulseResponse = response->channel(AudioBus::ChannelRight);
+#else
     String resourceName = String::format("IRC_%s_C_R0195_T%03d_P%03d", subjectName.utf8().data(), azimuth, positiveElevation);
 
     RefPtr<AudioBus> impulseResponse(AudioBus::loadPlatformResource(resourceName.utf8().data(), sampleRate));
@@ -130,6 +194,7 @@ bool HRTFElevation::calculateKernelsForAzimuthElevation(int azimuth, int elevati
     
     AudioChannel* leftEarImpulseResponse = impulseResponse->channelByType(AudioBus::ChannelLeft);
     AudioChannel* rightEarImpulseResponse = impulseResponse->channelByType(AudioBus::ChannelRight);
+#endif
 
     // Note that depending on the fftSize returned by the panner, we may be truncating the impulse response we just loaded in.
     const size_t fftSize = HRTFPanner::fftSizeForSampleRate(sampleRate);