Method panToTargetValue

src/core/StereoPannerNode.cpp:127–222

Handle de-zippered panning to a target value.

    // Handle de-zippered panning to a target value.
    virtual void panToTargetValue(const AudioBus * inputBus, AudioBus * outputBus, float panValue, size_t framesToProcess)
    {
        size_t numberOfInputChannels = inputBus->numberOfChannels();

        bool isInputSafe = inputBus && (inputBus->numberOfChannels() == Channels::Mono || inputBus->numberOfChannels() == Channels::Stereo) && framesToProcess <= inputBus->length();

        ASSERT(isInputSafe);

        if (!isInputSafe)
            return;

        bool isOutputSafe = outputBus && framesToProcess <= outputBus->length();

        ASSERT(isOutputSafe);

        if (!isOutputSafe)
            return;

        const float * sourceL = inputBus->channel(0)->data();
        const float * sourceR = numberOfInputChannels > Channels::Mono ? inputBus->channel(1)->data() : sourceL;

        float * destinationL = outputBus->channelByType(Channel::Left)->mutableData();
        float * destinationR = outputBus->channelByType(Channel::Right)->mutableData();

        if (!sourceL || !sourceR || !destinationL || !destinationR)
            return;

        float targetPan = clampTo(panValue, -1.f, 1.f);

        // Don't de-zipper on first render call.
        if (m_isFirstRender)
        {
            m_isFirstRender = false;
            m_pan = targetPan;
        }

        double gainL, gainR, panRadian;
        const double smoothingConstant = m_smoothingConstant;
        size_t n = framesToProcess;

        // For mono source case.
        if (numberOfInputChannels == Channels::Mono)
        {
            while (n--)
            {
                float inputL = *sourceL++;

                m_pan += (targetPan - m_pan) * smoothingConstant;

                // Pan from left to right [-1; 1] will be normalized as [0; 1].
                panRadian = (m_pan * 0.5 + 0.5) * LAB_HALF_PI;

                gainL = std::cos(panRadian);
                gainR = std::sin(panRadian);

                *destinationL++ = static_cast<float>(inputL * gainL);
                *destinationR++ = static_cast<float>(inputL * gainR);
            }