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 4278891593ebb2855ede7bf6e625ce3cd7481994..66a81d46c02d5f4e3d5534812e850f8af101f107 100644
--- a/Source/core/platform/audio/HRTFElevation.cpp
+++ b/Source/core/platform/audio/HRTFElevation.cpp
@@ -62,6 +62,38 @@ 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;
 
+// Lazily load a concatenated HRTF database for given subject and store it in a
+// local hash table to ensure quick efficient future retrievals.
+static AudioBus* getConcatenatedImpulseResponsesForSubject(const String& subjectName)
+{
+    typedef HashMap<String, AudioBus*> AudioBusMap;
+    DEFINE_STATIC_LOCAL(AudioBusMap, audioBusMap, ());
+
+    AudioBus* bus;
+    AudioBusMap::iterator iterator = audioBusMap.find(subjectName);
+    if (iterator == audioBusMap.end()) {
+        OwnPtr<AudioBus> concatenatedImpulseResponses = AudioBus::loadPlatformResource(subjectName.utf8().data(), ResponseSampleRate);
+        ASSERT(concatenatedImpulseResponses);
+        if (!concatenatedImpulseResponses)
+            return 0;
+
+        bus = concatenatedImpulseResponses.leakPtr();
+        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;
+}
+
 // 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,
@@ -105,31 +137,38 @@ bool HRTFElevation::calculateKernelsForAzimuthElevation(int azimuth, int elevati
     if (!isElevationGood)
         return false;
     
-    // Construct the resource name from the subject name, azimuth, and elevation, for example:
-    // "IRC_Composite_C_R0195_T015_P000"
+    int positiveElevation = elevation < 0 ? elevation + 360 : elevation;
+
     // Note: the passed in subjectName is not a string passed in via JavaScript or the web.
     // It's passed in as an internal ASCII identifier and is an implementation detail.

[Chris Rogers, 2013/04/23 19:51:44]

This comment used to be just before line 140 and you've left out part of the
comment.  The full comment is:

    // Construct the resource name from the subject name, azimuth, and
elevation, for example:
    // "IRC_Composite_C_R0195_T015_P000"
    // Note: the passed in subjectName is not a string passed in via JavaScript
or the web.
    // It's passed in as an internal ASCII identifier and is an implementation
detail.

-    int positiveElevation = elevation < 0 ? elevation + 360 : elevation;
+    AudioBus* bus(getConcatenatedImpulseResponsesForSubject(subjectName));
 
-    String resourceName = String::format("IRC_%s_C_R0195_T%03d_P%03d", subjectName.utf8().data(), azimuth, positiveElevation);
+    if (!bus)
+        return false;
 
-    OwnPtr<AudioBus> impulseResponse(AudioBus::loadPlatformResource(resourceName.utf8().data(), sampleRate));
+    int elevationIndex = positiveElevation / AzimuthSpacing;
+    if (positiveElevation > 90)
+        elevationIndex -= AzimuthSpacing;
 
-    ASSERT(impulseResponse.get());
-    if (!impulseResponse.get())
+    // 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;
-    
-    size_t responseLength = impulseResponse->length();
-    size_t expectedLength = static_cast<size_t>(256 * (sampleRate / 44100.0));
 
-    // Check number of channels and length.  For now these are fixed and known.
-    bool isBusGood = responseLength == expectedLength && impulseResponse->numberOfChannels() == 2;
-    ASSERT(isBusGood);
-    if (!isBusGood)
-        return false;
-    
-    AudioChannel* leftEarImpulseResponse = impulseResponse->channelByType(AudioBus::ChannelLeft);
-    AudioChannel* rightEarImpulseResponse = impulseResponse->channelByType(AudioBus::ChannelRight);
+    // 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;
+    OwnPtr<AudioBus> preSampleRateConvertedResponse = AudioBus::createBufferFromRange(bus, startFrame, stopFrame);
+    OwnPtr<AudioBus> response = AudioBus::createBySampleRateConverting(preSampleRateConvertedResponse.get(), false, sampleRate);
+    AudioChannel* leftEarImpulseResponse = response->channel(AudioBus::ChannelLeft);
+    AudioChannel* rightEarImpulseResponse = response->channel(AudioBus::ChannelRight);
 
     // 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);