/*

 * Copyright (C) 2010 Google Inc. All rights reserved.

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 * 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.

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 *     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

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 */

#include "HRTFKernel.h"

namespace WebCore {

// Takes the input audio channel |impulseP| as an input impulse response and calculates the average group delay.

// This represents the initial delay before the most energetic part of the impulse response.

// The sample-frame delay is removed from the |impulseP| impulse response, and this value  is returned.

// The |length| of the passed in |impulseP| must be must be a power of 2.

static float extractAverageGroupDelay(float* impulseP, size_t length)

{

    // Check for power-of-2.

    MOZ_ASSERT(length && (length & (length - 1)) == 0);

    FFTBlock estimationFrame(length);

    estimationFrame.PerformFFT(impulseP);

    float frameDelay = static_cast<float>(estimationFrame.ExtractAverageGroupDelay());

    estimationFrame.GetInverse(impulseP);

    return frameDelay;

}

HRTFKernel::HRTFKernel(float* impulseResponse, size_t length, float sampleRate)

    : m_frameDelay(0)

    , m_sampleRate(sampleRate)

{

    AlignedTArray<float> buffer;

    // copy to a 32-byte aligned buffer

    if (((uintptr_t)impulseResponse & 31) != 0) {

      buffer.SetLength(length);

      mozilla::PodCopy(buffer.Elements(), impulseResponse, length);

      impulseResponse = buffer.Elements();

    }

    // Determine the leading delay (average group delay) for the response.

    m_frameDelay = extractAverageGroupDelay(impulseResponse, length);

    // The FFT size (with zero padding) needs to be twice the response length

    // in order to do proper convolution.

    unsigned fftSize = 2 * length;

    // Quick fade-out (apply window) at truncation point

    // because the impulse response has been truncated.

    unsigned numberOfFadeOutFrames = static_cast<unsigned>(sampleRate / 4410); // 10 sample-frames @44.1KHz sample-rate

    MOZ_ASSERT(numberOfFadeOutFrames < length);

    if (numberOfFadeOutFrames < length) {

        for (unsigned i = length - numberOfFadeOutFrames; i < length; ++i) {

            float x = 1.0f - static_cast<float>(i - (length - numberOfFadeOutFrames)) / numberOfFadeOutFrames;

            impulseResponse[i] *= x;

        }

    }

    m_fftFrame = new FFTBlock(fftSize);

    m_fftFrame->PadAndMakeScaledDFT(impulseResponse, length);

}

// Interpolates two kernels with x: 0 -> 1 and returns the result.

nsReturnRef<HRTFKernel> HRTFKernel::createInterpolatedKernel(HRTFKernel* kernel1, HRTFKernel* kernel2, float x)

{

    MOZ_ASSERT(kernel1 && kernel2);

    if (!kernel1 || !kernel2)

        return nsReturnRef<HRTFKernel>();

    MOZ_ASSERT(x >= 0.0 && x < 1.0);

    x = mozilla::clamped(x, 0.0f, 1.0f);

    float sampleRate1 = kernel1->sampleRate();

    float sampleRate2 = kernel2->sampleRate();

    MOZ_ASSERT(sampleRate1 == sampleRate2);

    if (sampleRate1 != sampleRate2)

        return nsReturnRef<HRTFKernel>();

    float frameDelay = (1 - x) * kernel1->frameDelay() + x * kernel2->frameDelay();

    nsAutoPtr<FFTBlock> interpolatedFrame(

        FFTBlock::CreateInterpolatedBlock(*kernel1->fftFrame(), *kernel2->fftFrame(), x));

    return HRTFKernel::create(interpolatedFrame, frameDelay, sampleRate1);

}

} // namespace WebCore