Implement StereoPannerNode for robust stereo panning

Source/platform/audio/StereoPanner.cpp

Index: Source/platform/audio/StereoPanner.cpp
diff --git a/Source/platform/audio/StereoPanner.cpp b/Source/platform/audio/StereoPanner.cpp
new file mode 100644
index 0000000000000000000000000000000000000000..7eaa17253df532902aa83f6437b9dc7ca20fb5bd
--- /dev/null
+++ b/Source/platform/audio/StereoPanner.cpp
@@ -0,0 +1,159 @@
+// Copyright 2014 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "config.h"
+
+#if ENABLE(WEB_AUDIO)
+
+#include "platform/audio/StereoPanner.h"
+
+#include "platform/audio/AudioBus.h"
+#include "platform/audio/AudioUtilities.h"
+#include "wtf/MathExtras.h"
+#include <algorithm>
+
+// Use a 50ms smoothing / de-zippering time-constant.
+const float SmoothingTimeConstant = 0.050f;
+
+namespace blink {
+
+StereoPanner::StereoPanner(float sampleRate) : Spatializer(PanningModelEqualPower)
+    , m_isFirstRender(true)
+    , m_gainL(0.5)
+    , m_gainR(0.5)
+{
+    m_smoothingConstant = AudioUtilities::discreteTimeConstantForSampleRate(SmoothingTimeConstant, sampleRate);
+}
+
+void StereoPanner::panWithSampleAccurateValues(const AudioBus* inputBus, AudioBus* outputBus, const float* panValues, size_t framesToProcess)
+{
+    bool isInputSafe = inputBus
+        && (inputBus->numberOfChannels() == 1 || inputBus->numberOfChannels() == 2)
+        && framesToProcess <= inputBus->length();
+    ASSERT(isInputSafe);
+    if (!isInputSafe)
+        return;
+
+    unsigned numberOfInputChannels = inputBus->numberOfChannels();
+
+    bool isOutputSafe = outputBus
+        && outputBus->numberOfChannels() == 2
+        && framesToProcess <= outputBus->length();
+    ASSERT(isOutputSafe);
+    if (!isOutputSafe)
+        return;
+
+    const float* sourceL = inputBus->channel(0)->data();
+    const float* sourceR = numberOfInputChannels > 1 ? inputBus->channel(1)->data() : sourceL;
+    float* destinationL = outputBus->channelByType(AudioBus::ChannelLeft)->mutableData();
+    float* destinationR = outputBus->channelByType(AudioBus::ChannelRight)->mutableData();
+
+    if (!sourceL || !sourceR || !destinationL || !destinationR)
+        return;
+
+    // Cache in local variables.
+    double gainL = m_gainL;
+    double gainR = m_gainR;
+
+    int n = framesToProcess;
+
+    if (numberOfInputChannels == 1) { // For mono source case.
+        while (n--) {
+            float inputL = *sourceL++;
+            float panValue = clampTo(*panValues++, -1.0, 1.0);
+            float panPosition = (panValue * 0.5 + 0.5) * piOverTwoDouble;
+            gainL = std::cos(panPosition);
+            gainR = std::sin(panPosition);
+            *destinationL++ = static_cast<float>(inputL * gainL);
+            *destinationR++ = static_cast<float>(inputL * gainR);
+        }
+    } else { // For stereo source case.
+        while (n--) {
+            float inputL = *sourceL++;
+            float inputR = *sourceR++;
+            float panValue = clampTo(*panValues++, -1.0, 1.0);
+            float panPosition = (panValue * 0.5 + 0.5) * piOverTwoDouble;
+            gainL = std::cos(panPosition);
+            gainR = std::sin(panPosition);
+            *destinationL++ = static_cast<float>(inputL * gainL);
+            *destinationR++ = static_cast<float>(inputR * gainR);
+        }
+    }
+
+    m_gainL = gainL;
+    m_gainR = gainR;
+}
+
+void StereoPanner::panToTargetValue(const AudioBus* inputBus, AudioBus* outputBus, float panValue, size_t framesToProcess)
+{
+    bool isInputSafe = inputBus
+        && (inputBus->numberOfChannels() == 1 || inputBus->numberOfChannels() == 2)
+        && framesToProcess <= inputBus->length();
+    ASSERT(isInputSafe);
+    if (!isInputSafe)
+        return;
+
+    unsigned numberOfInputChannels = inputBus->numberOfChannels();
+
+    bool isOutputSafe = outputBus
+        && outputBus->numberOfChannels() == 2
+        && framesToProcess <= outputBus->length();
+    ASSERT(isOutputSafe);
+    if (!isOutputSafe)
+        return;
+
+    const float* sourceL = inputBus->channel(0)->data();
+    const float* sourceR = numberOfInputChannels > 1 ? inputBus->channel(1)->data() : sourceL;
+    float* destinationL = outputBus->channelByType(AudioBus::ChannelLeft)->mutableData();
+    float* destinationR = outputBus->channelByType(AudioBus::ChannelRight)->mutableData();
+
+    if (!sourceL || !sourceR || !destinationL || !destinationR)
+        return;
+
+    float panValueClamped = clampTo(panValue, -1.0, 1.0);
+    double targetGainL = std::cos(piOverTwoDouble * (panValueClamped * 0.5 + 0.5));
+    double targetGainR = std::sin(piOverTwoDouble * (panValueClamped * 0.5 + 0.5));
+
+    // Don't de-zipper on first render call.
+    if (m_isFirstRender) {
+        m_isFirstRender = false;
+        m_gainL = targetGainL;
+        m_gainR = targetGainR;
+    }
+
+    // Cache in local variables.
+    double gainL = m_gainL;
+    double gainR = m_gainR;
+
+    // Get local copy of smoothing constant.
+    const double SmoothingConstant = m_smoothingConstant;
+
+    int n = framesToProcess;
+
+    if (numberOfInputChannels == 1) { // For mono source case.
+        while (n--) {
+            float inputL = *sourceL++;
+            gainL += (targetGainL - gainL) * SmoothingConstant;
+            gainR += (targetGainR - gainR) * SmoothingConstant;
+            *destinationL++ = static_cast<float>(inputL * gainL);
+            *destinationR++ = static_cast<float>(inputL * gainR);
+        }
+    } else { // For stereo source case.
+        while (n--) {
+            float inputL = *sourceL++;
+            float inputR = *sourceR++;
+            gainL += (targetGainL - gainL) * SmoothingConstant;
+            gainR += (targetGainR - gainR) * SmoothingConstant;
+            *destinationL++ = static_cast<float>(inputL * gainL);
+            *destinationR++ = static_cast<float>(inputR * gainR);
+        }
+    }
+
+    m_gainL = gainL;
+    m_gainR = gainR;
+}
+
+} // namespace blink
+
+#endif // ENABLE(WEB_AUDIO)