Add support for WaveShaperNode.oversample

Source/core/platform/audio/UpSampler.cpp

+/*
+ * Copyright (C) 2013 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
+ *     documentation and/or other materials provided with the distribution.
+ * 3.  Neither the name of Apple Computer, Inc. ("Apple") nor the names of
+ *     its contributors may be used to endorse or promote products derived
+ *     from this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY APPLE AND ITS CONTRIBUTORS "AS IS" AND ANY
+ * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
+ * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL APPLE OR ITS CONTRIBUTORS BE LIABLE FOR ANY
+ * DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
+ * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
+ * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
+ * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
+ * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include "config.h"
+
+#if ENABLE(WEB_AUDIO)
+
+#include "core/platform/audio/UpSampler.h"
+
+#include "wtf/MathExtras.h"
+
+namespace WebCore {
+
+UpSampler::UpSampler(size_t inputBlockSize)
+    : m_inputBlockSize(inputBlockSize)
+    , m_kernel(DefaultKernelSize)
+    , m_tempBuffer(inputBlockSize)
+    , m_inputBuffer(inputBlockSize * 2)
+    , m_convolver(inputBlockSize)
+{
+    initializeKernel();
+}
+
+void UpSampler::initializeKernel()
+{
+    // Blackman window parameters.
+    double alpha = 0.16;
+    double a0 = 0.5 * (1.0 - alpha);
+    double a1 = 0.5;
+    double a2 = 0.5 * alpha;
+
+    int n = m_kernel.size();
+    int halfSize = n / 2;
+    double subsampleOffset = -0.5;
+
+    for (int i = 0; i < n; ++i) {
+        // Compute the sinc() with offset.
+        double s = piDouble * (i - halfSize - subsampleOffset);
+        double sinc = !s ? 1.0 : sin(s) / s;
+
+        // Compute Blackman window, matching the offset of the sinc().
+        double x = (i - subsampleOffset) / n;
+        double window = a0 - a1 * cos(2.0 * piDouble * x) + a2 * cos(4.0 * piDouble * x);
+
+        // Window the sinc() function.
+        m_kernel[i] = sinc * window;
+    }
+}
+
+void UpSampler::process(const float* sourceP, float* destP, size_t sourceFramesToProcess)
+{
+    ASSERT(sourceFramesToProcess == m_tempBuffer.size());
+    if (sourceFramesToProcess != m_tempBuffer.size())
+        return;
+
+    // Copy source samples to 2nd half of input buffer.
+    float* inputP = m_inputBuffer.data() + m_inputBlockSize;
+    memcpy(inputP, sourceP, sizeof(float) * sourceFramesToProcess);
+
+    int halfSize = m_kernel.size() / 2;
+
+    // Copy even sample-frames 0,2,4,6... (delayed by the linear phase delay) directly into destP.
+    for (unsigned i = 0; i < sourceFramesToProcess; ++i)
+        destP[i * 2] = inputP[i - halfSize];

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

Checks and assertions are needed to ensure that "i - halfSize" is always within
the range of m_inputBuffer. In particular, the kernel is sized based on
DefaultKernelSize but all of the buffers are sized based on inputBlockSize.

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

Done.

+
+    // Compute odd sample-frames 1,3,5,7...
+    float* oddSamplesP = m_tempBuffer.data();
+    m_convolver.process(&m_kernel, sourceP, oddSamplesP, sourceFramesToProcess);
+
+    for (unsigned i = 0; i < sourceFramesToProcess; ++i)
+        destP[i * 2 + 1] = oddSamplesP[i];
+
+    // Copy 2nd half of input buffer to 1st half.
+    memcpy(m_inputBuffer.data(), inputP, sizeof(float) * sourceFramesToProcess);

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

Again could you please explain to me why m_inputBuffer is necessary? It doesn't
look like it's exposed outside this class, and the convolver is operating
directly on the source data, not m_inputBuffer's data.

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

Added comment in header file.

+}
+
+void UpSampler::reset()
+{
+    m_convolver.reset();
+    m_inputBuffer.zero();
+}
+
+size_t UpSampler::latencyFrames() const
+{
+    // Divide by two since this is a linear phase kernel and the delay is at the center of the kernel.
+    return m_kernel.size() / 2;
+}
+
+} // namespace WebCore
+
+#endif // ENABLE(WEB_AUDIO)