Add support for WaveShaperNode.oversample

Source/modules/webaudio/WaveShaperDSPKernel.cpp

 /*
  * Copyright (C) 2011, Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1.  Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2.  Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 13 matching lines @@
 
 #include "config.h"
 
 #if ENABLE(WEB_AUDIO)
 
 #include "modules/webaudio/WaveShaperDSPKernel.h"
 
 #include "modules/webaudio/WaveShaperProcessor.h"
 #include <algorithm>
 
+const unsigned RenderingQuantum = 128;

[Ken Russell (switch to Gerrit), 2013/05/23 02:29:25]

Should be in an anonymous namespace.

[Chris Rogers, 2013/05/24 20:09:04]

This is const, so should already be limited to file scope in terms of linkage,
and also matches many other constants in the web audio code.

+
 using namespace std;
 
 namespace WebCore {
 
+WaveShaperDSPKernel::WaveShaperDSPKernel(WaveShaperProcessor* processor)
+    : AudioDSPKernel(processor)
+{
+    if (processor->oversample() != WaveShaperProcessor::OverSampleNone)
+        lazyInitializeOversampling();
+}
+
+void WaveShaperDSPKernel::lazyInitializeOversampling()
+{
+    ASSERT(isMainThread());
+
+    if (!m_tempBuffer) {
+        m_tempBuffer = adoptPtr(new AudioFloatArray(RenderingQuantum * 2));
+        m_tempBuffer2 = adoptPtr(new AudioFloatArray(RenderingQuantum * 4));
+        m_upSampler = adoptPtr(new UpSampler(RenderingQuantum));
+        m_downSampler = adoptPtr(new DownSampler(RenderingQuantum * 2));
+        m_upSampler2 = adoptPtr(new UpSampler(RenderingQuantum * 2));
+        m_downSampler2 = adoptPtr(new DownSampler(RenderingQuantum * 4));
+    }
+}
+
 void WaveShaperDSPKernel::process(const float* source, float* destination, size_t framesToProcess)
 {
+    switch (waveShaperProcessor()->oversample()) {
+    case WaveShaperProcessor::OverSampleNone:
+        processCurve(source, destination, framesToProcess);
+        break;
+    case WaveShaperProcessor::OverSample2x:
+        processCurve2x(source, destination, framesToProcess);
+        break;
+    case WaveShaperProcessor::OverSample4x:
+        processCurve4x(source, destination, framesToProcess);
+        break;
+
+    default:
+        ASSERT_NOT_REACHED();
+    }
+}
+
+void WaveShaperDSPKernel::processCurve(const float* source, float* destination, size_t framesToProcess)
+{
     ASSERT(source && destination && waveShaperProcessor());
 
     Float32Array* curve = waveShaperProcessor()->curve();
     if (!curve) {
         // Act as "straight wire" pass-through if no curve is set.
         memcpy(destination, source, sizeof(float) * framesToProcess);
         return;
     }
 
     float* curveData = curve->data();
     int curveLength = curve->length();
 
     ASSERT(curveData);
 
     if (!curveData || !curveLength) {
         memcpy(destination, source, sizeof(float) * framesToProcess);
         return;
     }
 
     // Apply waveshaping curve.
     for (unsigned i = 0; i < framesToProcess; ++i) {
         const float input = source[i];
 
-        // Calculate an index based on input -1 -> +1 with 0 being at the center of the curve data.
-        int index = (curveLength * (input + 1)) / 2;
+        // Calculate a virtual index based on input -1 -> +1 with 0 being at the center of the curve data.
+        // Then linearly interpolate between the two points in the curve.
+        double virtualIndex = 0.5 * (input + 1) * curveLength;
+        int index1 = static_cast<int>(virtualIndex);
+        int index2 = index1 + 1;
+        double interpolationFactor = virtualIndex - index1;
 
         // Clip index to the input range of the curve.
         // This takes care of input outside of nominal range -1 -> +1
-        index = max(index, 0);
-        index = min(index, curveLength - 1);
-        destination[i] = curveData[index];
+        index1 = max(index1, 0);
+        index1 = min(index1, curveLength - 1);
+        index2 = max(index2, 0);
+        index2 = min(index2, curveLength - 1);
+
+        double value1 = curveData[index1];
+        double value2 = curveData[index2];
+
+        double output = (1.0 - interpolationFactor) * value1 + interpolationFactor * value2;
+        destination[i] = output;
     }
 }
 
+void WaveShaperDSPKernel::processCurve2x(const float* source, float* destination, size_t framesToProcess)
+{
+    float* tempP = m_tempBuffer->data();
+
+    m_upSampler->process(source, tempP, framesToProcess);

[Ken Russell (switch to Gerrit), 2013/05/23 02:29:25]

Some assertions and checks are needed to ensure that framesToProcess is properly
related to RenderingQuantum.

[Chris Rogers, 2013/05/24 20:09:04]

Done.

+
+    // Process at 2x up-sampled rate.
+    processCurve(tempP, tempP, framesToProcess * 2);
+
+    m_downSampler->process(tempP, destination, framesToProcess * 2);
+}
+
+void WaveShaperDSPKernel::processCurve4x(const float* source, float* destination, size_t framesToProcess)
+{
+    float* tempP = m_tempBuffer->data();
+    float* tempP2 = m_tempBuffer2->data();
+
+    m_upSampler->process(source, tempP, framesToProcess);

[Ken Russell (switch to Gerrit), 2013/05/23 02:29:25]

Same here regarding framesToProcess.

[Chris Rogers, 2013/05/24 20:09:04]

Done.

+    m_upSampler2->process(tempP, tempP2, framesToProcess * 2);
+
+    // Process at 4x up-sampled rate.
+    processCurve(tempP2, tempP2, framesToProcess * 4);
+
+    m_downSampler2->process(tempP2, tempP, framesToProcess * 4);
+    m_downSampler->process(tempP, destination, framesToProcess * 2);
+}
+
+void WaveShaperDSPKernel::reset()
+{
+    if (m_upSampler) {
+        m_upSampler->reset();
+        m_downSampler->reset();
+        m_upSampler2->reset();
+        m_downSampler2->reset();
+    }
+}
+
+double WaveShaperDSPKernel::latencyTime() const
+{
+    size_t latencyFrames = 0;
+    WaveShaperDSPKernel* kernel = const_cast<WaveShaperDSPKernel*>(this);
+
+    switch (kernel->waveShaperProcessor()->oversample()) {
+    case WaveShaperProcessor::OverSampleNone:
+        break;
+    case WaveShaperProcessor::OverSample2x:
+        latencyFrames += m_upSampler->latencyFrames();
+        latencyFrames += m_downSampler->latencyFrames();
+        break;
+    case WaveShaperProcessor::OverSample4x:
+        {
+            // Account for first stage upsampling.
+            latencyFrames += m_upSampler->latencyFrames();
+            latencyFrames += m_downSampler->latencyFrames();
+
+            // Account for second stage upsampling.
+            // and divide by 2 to get back down to the regular sample-rate.
+            size_t latencyFrames2 = (m_upSampler2->latencyFrames() + m_downSampler2->latencyFrames()) / 2;
+            latencyFrames += latencyFrames2;
+            break;
+        }
+    default:
+        ASSERT_NOT_REACHED();
+    }
+
+    return static_cast<double>(latencyFrames) / sampleRate();
+}
+
 } // namespace WebCore
 
 #endif // ENABLE(WEB_AUDIO)