Add support for WaveShaperNode.oversample

Source/core/platform/audio/DownSampler.h

 /*
  * 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:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 10 matching lines @@
  * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
  * OWNER OR 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.
  */
 
-#ifndef Animation_h
-#define Animation_h
+#ifndef DownSampler_h
+#define DownSampler_h
 
-#include "core/animation/AnimationEffect.h"
-#include "core/animation/TimedItem.h"
-#include "wtf/RefPtr.h"
+#include "core/platform/audio/AudioArray.h"
+#include "core/platform/audio/DirectConvolver.h"
 
 namespace WebCore {
 
-class Element;
+// DownSampler down-samples the source stream by a factor of 2x.
 
-class Animation FINAL : public TimedItem {
+class DownSampler {
+public:
+    DownSampler(size_t inputBlockSize);
 
-public:
-    static PassRefPtr<Animation> create(PassRefPtr<Element>, PassRefPtr<AnimationEffect>, const Timing&);
-    virtual ~Animation();
+    // The destination buffer |destP| is of size sourceFramesToProcess / 2.
+    void process(const float* sourceP, float* destP, size_t sourceFramesToProcess);
 
-    const AnimationEffect::CompositableValueMap* compositableValues() const
-    {
-        ASSERT(m_compositableValues);
-        return m_compositableValues.get();
-    }
+    void reset();
 
-protected:
-    virtual void applyEffects(bool previouslyActiveOrInEffect);
-    virtual void clearEffects();
-    virtual void updateChildrenAndEffects(bool) const OVERRIDE FINAL;
+    // Latency based on the destination sample-rate.
+    size_t latencyFrames() const;
 
 private:
-    Animation(PassRefPtr<Element>, PassRefPtr<AnimationEffect>, const Timing&);
+    enum { DefaultKernelSize = 256 };
 
-    RefPtr<Element> m_target;
-    RefPtr<AnimationEffect> m_effect;
-    bool m_isInTargetActiveAnimationsList;
-    OwnPtr<AnimationEffect::CompositableValueMap> m_compositableValues;
+    size_t m_inputBlockSize;
+
+    // Computes ideal band-limited half-band filter coefficients.
+    // In other words, filter out all frequencies higher than 0.25 * Nyquist.
+    void initializeKernel();
+    AudioFloatArray m_reducedKernel;
+
+    // Half-band filter.
+    DirectConvolver m_convolver;
+
+    AudioFloatArray m_tempBuffer;
+
+    // Used as delay-line (FIR filter history) for the input samples to account for the 0.5 term right in the middle of the kernel.
+    AudioFloatArray m_inputBuffer;
 };
 
 } // namespace WebCore
 
-#endif
+#endif // DownSampler_h