Method decodeFFT

src/core/PanadapterStream.cpp:862–948

// ─── FFT decode ──────────────────────────────────────────────────────────────

void PanadapterStream::decodeFFT(const uchar* raw, int totalBytes, bool hasTrailer, quint32 streamId)
{
    static constexpr int FFT_SUBHEADER_BYTES = 12;
    if (totalBytes < VITA49_HEADER_BYTES + FFT_SUBHEADER_BYTES) return;

    const uchar* sub = raw + VITA49_HEADER_BYTES;
    const quint16 startBin   = qFromBigEndian<quint16>(sub + 0);
    const quint16 numBins    = qFromBigEndian<quint16>(sub + 2);
    const quint16 binSize    = qFromBigEndian<quint16>(sub + 4);
    const quint16 totalBins  = qFromBigEndian<quint16>(sub + 6);
    const quint32 frameIndex = qFromBigEndian<quint32>(sub + 8);

    if (numBins == 0 || binSize == 0 || totalBins == 0) return;

    const int binDataOffset = VITA49_HEADER_BYTES + FFT_SUBHEADER_BYTES;
    int binDataBytes = numBins * binSize;
    const int available = totalBytes - binDataOffset - (hasTrailer ? 4 : 0);
    if (available < binDataBytes) {
        binDataBytes = available;
        if (binDataBytes <= 0) return;
    }

    const uchar* binData = raw + binDataOffset;

    // Per-stream frame assembly
    auto& frame = m_frames[streamId];
    if (frameIndex != frame.frameIndex) {
        if (frame.totalBins > 0 && !frame.isComplete())
            PerfTelemetry::instance().recordFrameRestart(PerfTelemetry::FrameKind::Panadapter);
        frame.reset(frameIndex, totalBins);
    }

    if (startBin + numBins > static_cast<quint16>(frame.buf.size()))
        return;

    for (quint16 i = 0; i < numBins; ++i)
        frame.buf[startBin + i] = qFromBigEndian<quint16>(binData + i * 2);

    frame.binsReceived += numBins;

    if (!frame.isComplete()) return;

    // Convert to dBm using per-stream range
    QPair<float,float> dbmRange;
    int yPixVal;
    {
        QMutexLocker lock(&m_streamMutex);
        dbmRange = m_dbmRanges.value(streamId, {-130.0f, -40.0f});
        yPixVal = m_yPixels.value(streamId, 700);
    }
    auto [minDbm, maxDbm] = dbmRange;
    const float range = maxDbm - minDbm;
    if (range <= 0.0f) return;

    const int   count = frame.buf.size();
    QVector<float> bins(count);

    int effectiveYPixels = std::max(yPixVal, 2);