Method apply

core/src/core/path_effect.cpp:103–226

Rendering the SH and EQ coefficients for pathing involves the following steps: 1. EQ is applied to the dry audio. 2. The EQ-filtered audio is scaled by each SH coefficient in turn and combined into an Ambisonics buffer.

// 1. EQ is applied to the dry audio.
// 2. The EQ-filtered audio is scaled by each SH coefficient in turn and combined into an Ambisonics buffer.
AudioEffectState PathEffect::apply(const PathEffectParams& params,
                                   const AudioBuffer& in,
                                   AudioBuffer& out)
{
    assert(in.numSamples() == out.numSamples());
    assert(in.numChannels() == 1);

    out.makeSilent();

    if (mSpatialize)
    {
        // todo: assert?

        // apply eq to mono input
        EQEffectParams eqParams{};
        eqParams.gains = params.eqCoeffs;

        float eqGains[Bands::kNumBands] = {0};
        if (params.normalizeEQ)
        {
            memcpy(eqGains, params.eqCoeffs, Bands::kNumBands * sizeof(float));

            auto overallGain = 1.0f;
            EQEffect::normalizeGains(eqGains, overallGain);

            eqParams.gains = eqGains;
        }

        mEQEffect.apply(eqParams, in, mEQBuffer);

        for (auto i = 0; i < SphericalHarmonics::numCoeffsForOrder(params.order); ++i)
        {
            (*mAmbisonicsBuffer)[i][0] = params.shCoeffs[i];
        }

        // rotate the sh coeffs
        AmbisonicsRotateEffectParams ambisonicsRotateParams{};
        ambisonicsRotateParams.orientation = params.listener;
        ambisonicsRotateParams.order = params.order;

        mAmbisonicsRotateEffect->apply(ambisonicsRotateParams, *mAmbisonicsBuffer, *mAmbisonicsBuffer);

        if (params.binaural)
        {
            // blend hrtf
            memset(mHRTF.flatData(), 0, mHRTF.totalSize() * sizeof(complex_t));

            auto cosine = cosf((137.9f * Math::kDegreesToRadians) / (params.order + 1.51f));
            for (auto l = 0, i = 0; l <= params.order; ++l)
            {
                auto scalar = SphericalHarmonics::legendre(l, cosine);
                for (auto m = -l; m <= l; ++m, ++i)
                {
                    const complex_t* hrtfForChannel[2] = {nullptr, nullptr};
                    params.hrtf->ambisonicsHRTF(i, hrtfForChannel);

                    for (auto k = 0; k < IHRTFMap::kNumEars; ++k)
                    {