Method paintEvent

src/gui/SpectrumWidget.cpp:9365–9677

#else // !AETHER_GPU_SPECTRUM

void SpectrumWidget::paintEvent(QPaintEvent* ev)
{
    if (width() <= 0 || height() <= freqScaleH() + DIVIDER_H + 2) return;

#ifdef AETHER_GPU_SPECTRUM
    // GPU mode: render() handles everything via QRhi. Skip the full
    // QPainter path to avoid redundant rendering + compositing overhead.
    // This is the single biggest CPU optimization on macOS (100% → 20%).
    if (m_rhiInitialized) {
        SPECTRUM_BASE_CLASS::paintEvent(ev);
        return;
    }
#endif

    // panstats: software-path paint cost (GPU builds only reach here before
    // QRhi init or after GPU teardown).
    m_panStats.paintEvents++;
    struct PaintCost {
        quint64& acc;
        QElapsedTimer t;
        explicit PaintCost(quint64& a) : acc(a) { t.start(); }
        ~PaintCost() { acc += static_cast<quint64>(t.nsecsElapsed() / 1000); }
    } panStatsPaintCost(m_panStats.paintUs);
    Q_UNUSED(ev);

    QElapsedTimer frameTimer;
    frameTimer.start();

    QPainter p(this);
    p.setRenderHint(QPainter::Antialiasing, false);

    const int chromeH  = freqScaleH() + DIVIDER_H;
    const int contentH = height() - chromeH;
    const int specH    = static_cast<int>(contentH * m_spectrumFrac);
    const int wfH      = contentH - specH;

    const int divY     = specH;
    const int scaleY   = specH + DIVIDER_H;
    const int wfY      = scaleY + freqScaleH();

    const QRect specRect (0, 0,       width(), specH);
    const QRect divRect  (0, divY,    width(), DIVIDER_H);
    const QRect scaleRect(0, scaleY,  width(), freqScaleH());
    const QRect wfRect   (0, wfY,     width(), wfH);

    const bool is3D = (m_spectrumRenderMode == SpectrumRenderMode::Mode3D);

    // Spectrum region: the 3DSS surface, or the classic bg + grid + FFT trace.
    // 3DSS replaces ONLY the spectrum trace — the divider, freq scale, waterfall,
    // overlays, and scales below run identically in both modes.
    if (is3D) {
        // Cap the software surface (like the GPU path) so a HiDPI/maximized
        // window doesn't rebuild a multi-megapixel QImage every frame; the
        // surface is intrinsically low-res, so stretch it on draw.
        const QImage& surf =
            buildDssImage(specRect.size().boundedTo(QSize(kDssMaxW, kDssMaxH)), 0);
        if (!surf.isNull()) {
            p.drawImage(specRect, surf);