channelrhiview.cpp

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//=============================================================================================================
 
//=============================================================================================================
// INCLUDES
//=============================================================================================================
 
#include "channelrhiview.h"
 
#include <rhi/qrhi.h>
#include <rhi/qshader.h>
#include <QFile>
 
//=============================================================================================================
// QT INCLUDES
//=============================================================================================================
 
#include <QApplication>
#include <QPropertyAnimation>
#include <QWheelEvent>
#include <QMouseEvent>
#include <QResizeEvent>
#include <QPainter>
#include <QPolygonF>
#include <QtMath>
 
#include <utility>
 
//=============================================================================================================
// USED NAMESPACES
//=============================================================================================================
 
using namespace DISPLIB;
 
//=============================================================================================================
// Uniform block layout — must match channeldata.vert / channeldata.frag
//=============================================================================================================
 
namespace
{
// Byte offsets inside one aligned UBO slot
constexpr int kUboOffsetColor = 0;           // vec4  (16 bytes)
constexpr int kUboOffsetFirstSample = 16;    // float
constexpr int kUboOffsetScrollSample = 20;   // float
constexpr int kUboOffsetSampPerPixel = 24;   // float
constexpr int kUboOffsetViewWidth = 28;      // float
constexpr int kUboOffsetViewHeight = 32;     // float
constexpr int kUboOffsetChannelYCenter = 36; // float
constexpr int kUboOffsetChannelYRange = 40;  // float
constexpr int kUboOffsetAmplitudeMax = 44;   // float
constexpr int kUboOffsetShowClipping = 48;   // float
// Total used: 52 bytes  — padded to m_uboStride (≥ 256) per dynamic offset rules.
 
constexpr int kMaxChannels = 1024; // Upper hard limit for UBO pre-allocation
 
} // namespace
 
//=============================================================================================================
// HELPERS
//=============================================================================================================
 
static QShader loadShader(const QString& filename)
{
    QFile f(filename);
    if (!f.open(QIODevice::ReadOnly)) {
        qWarning() << "ChannelRhiView: cannot open shader" << filename;
        return {};
    }
    return QShader::fromSerialized(f.readAll());
}
 
static void writeFloat(quint8* base, int byteOffset, float v)
{
    memcpy(base + byteOffset, &v, sizeof(float));
}
 
static void writeFloats(quint8* base, int byteOffset, const float* data, int count)
{
    memcpy(base + byteOffset, data, count * sizeof(float));
}
 
//=============================================================================================================
// DEFINE MEMBER METHODS
//=============================================================================================================
 
//=============================================================================================================
// CrosshairOverlay — lightweight transparent child widget for crosshair/scalebar
// painting.  Sits on top of the QRhiWidget and repaints independently so that
// mouse-tracking updates do NOT trigger the expensive GPU render pipeline.
//=============================================================================================================
 
class CrosshairOverlay : public QWidget
{
public:
    explicit CrosshairOverlay(ChannelRhiView* parent)
    : QWidget(parent)
    , m_view(parent)
    {
        setAttribute(Qt::WA_TransparentForMouseEvents);
        setAttribute(Qt::WA_NoSystemBackground);
        setAttribute(Qt::WA_TranslucentBackground);
        setMouseTracking(false);
    }
 
    void syncSize()
    {
        setGeometry(0, 0, parentWidget()->width(), parentWidget()->height());
    }
 
protected:
    void paintEvent(QPaintEvent*) override
    {
        if (!m_view)
            return;
        QPainter p(this);
        p.setRenderHint(QPainter::Antialiasing, false);
 
        if (m_view->crosshairEnabled())
            m_view->drawCrosshair(p);
        if (m_view->scalebarsVisible())
            m_view->drawScalebars(p);
        if (m_view->rulerActive())
            m_view->drawRulerOverlay(p);
        if (m_view->annotationSelecting())
            m_view->drawAnnotationSelectionOverlay(p);
    }
 
private:
    ChannelRhiView* m_view;
};
 
ChannelRhiView::ChannelRhiView(QWidget* parent)
: QRhiWidget(parent)
{
    setFocusPolicy(Qt::StrongFocus);
    setMouseTracking(true);
    setContextMenuPolicy(Qt::PreventContextMenu); // prevent right-click context menu
 
    m_overlay = new CrosshairOverlay(this);
    m_overlay->raise();
    m_overlay->show();
 
    // Platform-specific backend selection
#if defined(WASMBUILD) || defined(__EMSCRIPTEN__)
    setApi(QRhiWidget::Api::OpenGL); // WebGL 2
#elif defined(Q_OS_MACOS) || defined(Q_OS_IOS)
    setApi(QRhiWidget::Api::Metal);
#elif defined(Q_OS_WIN)
    setApi(QRhiWidget::Api::Direct3D11);
#else
    setApi(QRhiWidget::Api::OpenGL);
#endif
    setSampleCount(1);
    // Force a native window so Metal/OpenGL can create their backing surface.
    // Without this, QRhiWidget may fail to obtain an NSView handle on macOS.
    setAttribute(Qt::WA_NativeWindow);
 
    // Repaint overlays (bands + event lines) when the app regains focus.
    // The ruler overlay still uses QPainter and needs an explicit refresh.
    connect(qApp, &QApplication::applicationStateChanged,
            this, [this](Qt::ApplicationState s) {
                if (s == Qt::ApplicationActive)
                    update();
            });
}
 
//=============================================================================================================
 
ChannelRhiView::~ChannelRhiView() = default;
 
//=============================================================================================================
 
void ChannelRhiView::setModel(ChannelDataModel* model)
{
    if (m_model == model)
        return;
    if (m_model) {
        disconnect(m_model, &ChannelDataModel::dataChanged, this, nullptr);
        disconnect(m_model, &ChannelDataModel::metaChanged, this, nullptr);
    }
    m_model = model;
    if (m_model) {
        connect(m_model, &ChannelDataModel::dataChanged, this, [this] {
            m_vboDirty = true;
            update();
        });
        connect(m_model, &ChannelDataModel::metaChanged, this, [this] {
            m_vboDirty = true;
            m_pipelineDirty = true;
            update();
        });
    }
    m_vboDirty = true;
    m_pipelineDirty = true;
    update();
}
 
//=============================================================================================================
 
float ChannelRhiView::clampScrollSample(float sample) const
{
    // Never scroll before the first available sample
    if (m_model && m_model->totalSamples() > 0)
        sample = qMax(sample, static_cast<float>(m_model->firstSample()));
    else
        sample = qMax(sample, 0.f);
 
    // Never scroll past the file end (clamp upper bound when file bounds are known)
    if (m_lastFileSample >= 0) {
        float maxScroll = static_cast<float>(m_lastFileSample - visibleSampleCount() + 1);
        maxScroll = qMax(maxScroll, static_cast<float>(m_firstFileSample));
        sample = qMin(sample, maxScroll);
    }
    return sample;
}
 
//=============================================================================================================
 
void ChannelRhiView::setScrollSample(float sample)
{
    sample = clampScrollSample(sample);
 
    // Exact: a relative fuzzy compare ignores steps below 1e-5 of the position (10 samples at 10^6)
    if (m_scrollSample == sample)
        return;
 
    m_scrollSample = sample;
 
    // Check whether the prefetch window is still valid
    float visible = width() * m_samplesPerPixel;
    float margin = m_prefetchFactor * visible;
    if (sample < m_vboWindowFirst + margin ||
        sample + visible > m_vboWindowLast - margin) {
        m_vboDirty = true;
    }
 
    // Overlay prefetch: only rebuild when scroll exceeds the cached sample range.
    // The shader handles bands via uniforms, so we only need to rebuild when
    // annotations/events would be outside the cached texture.
    if (m_overlayTotalSamples <= 0.f ||
        sample < m_overlayFirstSample ||
        sample + visible > m_overlayFirstSample + m_overlayTotalSamples) {
        m_overlayDirty = true;
    }
 
    emit scrollSampleChanged(m_scrollSample);
    update();
}
 
//=============================================================================================================
 
void ChannelRhiView::setSamplesPerPixel(float spp)
{
    spp = qMax(spp, 1e-4f);
    if (qFuzzyCompare(m_samplesPerPixel, spp))
        return;
    m_samplesPerPixel = spp;
    m_vboDirty = true; // zoom change → decimation changes
    m_overlayDirty = true;
    emit samplesPerPixelChanged(m_samplesPerPixel);
    update();
}
 
//=============================================================================================================
 
void ChannelRhiView::scrollTo(float targetSample, int durationMs)
{
    // A running animation would keep writing scrollSample and fight the new one
    stopScrollAnimations();
    if (durationMs <= 0) {
        setScrollSample(targetSample);
        return;
    }
    m_scrollTarget = clampScrollSample(targetSample);
    m_pScrollAnim = new QPropertyAnimation(this, "scrollSample", this);
    m_pScrollAnim->setDuration(durationMs);
    m_pScrollAnim->setEasingCurve(QEasingCurve::OutCubic);
    m_pScrollAnim->setStartValue(m_scrollSample);
    m_pScrollAnim->setEndValue(m_scrollTarget);
    m_pScrollAnim->start(QAbstractAnimation::DeleteWhenStopped);
}
 
//=============================================================================================================
 
void ChannelRhiView::stopScrollAnimations()
{
    if (m_pScrollAnim) {
        m_pScrollAnim->stop();
    }
    if (m_pInertialAnim) {
        m_pInertialAnim->stop();
        m_pInertialAnim = nullptr;
    }
}
 
//=============================================================================================================
 
void ChannelRhiView::scrollBy(float deltaSamples, int durationMs)
{
    scrollTo((m_pScrollAnim ? m_scrollTarget : m_scrollSample) + deltaSamples, durationMs);
}
 
//=============================================================================================================
 
void ChannelRhiView::zoomTo(float targetSpp, int durationMs)
{
    targetSpp = qMax(targetSpp, 1e-4f);
    if (durationMs <= 0) {
        setSamplesPerPixel(targetSpp);
        return;
    }
    auto* anim = new QPropertyAnimation(this, "samplesPerPixel", this);
    anim->setDuration(durationMs);
    anim->setEasingCurve(QEasingCurve::OutCubic);
    anim->setStartValue(m_samplesPerPixel);
    anim->setEndValue(targetSpp);
    anim->start(QAbstractAnimation::DeleteWhenStopped);
}
 
//=============================================================================================================
 
void ChannelRhiView::setBackgroundColor(const QColor& color)
{
    m_bgColor = color;
    m_overlayDirty = true;
    update();
}
 
//=============================================================================================================
 
void ChannelRhiView::setPrefetchFactor(float factor)
{
    m_prefetchFactor = qMax(factor, 0.1f);
}
 
//=============================================================================================================
 
int ChannelRhiView::visibleFirstSample() const
{
    return static_cast<int>(m_scrollSample);
}
 
//=============================================================================================================
 
int ChannelRhiView::visibleSampleCount() const
{
    return static_cast<int>(width() * m_samplesPerPixel);
}
 
//=============================================================================================================
 
void ChannelRhiView::setFirstVisibleChannel(int ch)
{
    int maxFirst = qMax(0, totalLogicalChannels() - m_visibleChannelCount);
    ch = qBound(0, ch, maxFirst);
    if (ch == m_firstVisibleChannel)
        return;
    m_firstVisibleChannel = ch;
    m_vboDirty = true;
    m_pipelineDirty = true;
    emit channelOffsetChanged(m_firstVisibleChannel);
    update();
}
 
//=============================================================================================================
 
void ChannelRhiView::setVisibleChannelCount(int count)
{
    count = qMax(1, count);
    if (count == m_visibleChannelCount)
        return;
    m_visibleChannelCount = count;
    m_vboDirty = true;
    m_pipelineDirty = true;
    update();
}
 
//=============================================================================================================
 
void ChannelRhiView::setFrozen(bool frozen)
{
    m_frozen = frozen;
    if (m_frozen) {
        stopScrollAnimations();
    }
}
 
//=============================================================================================================
 
void ChannelRhiView::setGridVisible(bool visible)
{
    if (visible == m_gridVisible)
        return;
    m_gridVisible = visible;
    m_overlayDirty = true;
    update();
}
 
//=============================================================================================================
 
void ChannelRhiView::setSfreq(float sfreq)
{
    m_sfreq = qMax(sfreq, 0.f);
    m_overlayDirty = true;
    update();
}
 
//=============================================================================================================
 
void ChannelRhiView::setFirstFileSample(int first)
{
    if (first == m_firstFileSample)
        return;
    m_firstFileSample = first;
    m_overlayDirty = true;
    update();
}
 
//=============================================================================================================
 
void ChannelRhiView::setLastFileSample(int last)
{
    m_lastFileSample = last;
}
 
//=============================================================================================================
 
void ChannelRhiView::setHideBadChannels(bool hide)
{
    if (m_hideBadChannels == hide)
        return;
 
    const int previousFirstVisibleChannel = m_firstVisibleChannel;
    m_hideBadChannels = hide;
    const int maxFirst = qMax(0, totalLogicalChannels() - m_visibleChannelCount);
    m_firstVisibleChannel = qBound(0, m_firstVisibleChannel, maxFirst);
    if (m_firstVisibleChannel != previousFirstVisibleChannel) {
        emit channelOffsetChanged(m_firstVisibleChannel);
    }
    m_vboDirty = true;
    m_pipelineDirty = true;
    update();
}
 
//=============================================================================================================
 
void ChannelRhiView::setWheelScrollsChannels(bool channelsMode)
{
    m_wheelScrollsChannels = channelsMode;
}
 
//=============================================================================================================
 
void ChannelRhiView::setScrollSpeedFactor(float factor)
{
    m_scrollSpeedFactor = qBound(0.25f, factor, 4.0f);
}
 
//=============================================================================================================
 
void ChannelRhiView::setCrosshairEnabled(bool enabled)
{
    if (m_crosshairEnabled == enabled)
        return;
    m_crosshairEnabled = enabled;
    if (enabled) {
        setMouseTracking(true);
    } else {
        setMouseTracking(false);
        m_crosshairX = m_crosshairY = -1;
    }
    update();
}
 
//=============================================================================================================
 
void ChannelRhiView::setScalebarsVisible(bool visible)
{
    if (m_scalebarsVisible == visible)
        return;
    m_scalebarsVisible = visible;
    update();
}
 
//=============================================================================================================
 
void ChannelRhiView::setButterflyMode(bool enabled)
{
    if (m_butterflyMode == enabled)
        return;
    m_butterflyMode = enabled;
    m_vboDirty = true;
    m_pipelineDirty = true;
    m_overlayDirty = true;
    update();
}
 
//=============================================================================================================
 
QVector<ChannelRhiView::ButterflyTypeGroup> ChannelRhiView::butterflyTypeGroups() const
{
    QVector<ButterflyTypeGroup> groups;
    if (!m_model)
        return groups;
 
    const QVector<int> allCh = effectiveChannelIndices();
    QMap<QString, int> typeToGroup; // typeLabel → index in groups
 
    for (int ch : allCh) {
        auto info = m_model->channelInfo(ch);
        if (m_hideBadChannels && info.bad)
            continue;
        int gIdx;
        if (typeToGroup.contains(info.typeLabel)) {
            gIdx = typeToGroup[info.typeLabel];
        } else {
            gIdx = groups.size();
            typeToGroup[info.typeLabel] = gIdx;
            ButterflyTypeGroup g;
            g.typeLabel = info.typeLabel;
            g.color = info.color;
            g.amplitudeMax = info.amplitudeMax;
            groups.append(g);
        }
        groups[gIdx].channelIndices.append(ch);
    }
    return groups;
}
 
//=============================================================================================================
 
int ChannelRhiView::butterflyLaneCount() const
{
    if (!m_model)
        return 0;
    const QVector<int> allCh = effectiveChannelIndices();
    QSet<QString> types;
    for (int ch : allCh) {
        auto info = m_model->channelInfo(ch);
        if (m_hideBadChannels && info.bad)
            continue;
        types.insert(info.typeLabel);
    }
    return types.size();
}
 
//=============================================================================================================
 
void ChannelRhiView::setChannelIndices(const QVector<int>& indices)
{
    const int previousFirstVisibleChannel = m_firstVisibleChannel;
    m_filteredChannels = indices;
    // Clamp scroll to new range
    int maxFirst = qMax(0, totalLogicalChannels() - m_visibleChannelCount);
    m_firstVisibleChannel = qBound(0, m_firstVisibleChannel, maxFirst);
    if (m_firstVisibleChannel != previousFirstVisibleChannel) {
        emit channelOffsetChanged(m_firstVisibleChannel);
    }
    m_vboDirty = true;
    m_pipelineDirty = true;
    update();
}
 
//=============================================================================================================
 
int ChannelRhiView::totalLogicalChannels() const
{
    return effectiveChannelIndices().size();
}
 
//=============================================================================================================
 
int ChannelRhiView::actualChannelAt(int logicalIdx) const
{
    const QVector<int> indices = effectiveChannelIndices();
    if (logicalIdx < 0 || logicalIdx >= indices.size())
        return -1;
    return indices.at(logicalIdx);
}
 
//=============================================================================================================
 
QVector<int> ChannelRhiView::effectiveChannelIndices() const
{
    QVector<int> indices;
 
    if (!m_model) {
        return indices;
    }
 
    if (m_filteredChannels.isEmpty()) {
        indices.reserve(m_model->channelCount());
        for (int channelIndex = 0; channelIndex < m_model->channelCount(); ++channelIndex) {
            indices.append(channelIndex);
        }
    } else {
        indices = m_filteredChannels;
    }
 
    if (!m_hideBadChannels) {
        return indices;
    }
 
    QVector<int> visibleIndices;
    visibleIndices.reserve(indices.size());
    for (int channelIndex : std::as_const(indices)) {
        if (channelIndex < 0) {
            continue;
        }
 
        const ChannelDisplayInfo info = m_model->channelInfo(channelIndex);
        if (!info.bad) {
            visibleIndices.append(channelIndex);
        }
    }
 
    return visibleIndices;
}
 
//=============================================================================================================
 
void ChannelRhiView::setEvents(const QVector<EventMarker>& events)
{
    m_events = events;
    m_overlayDirty = true;
    update();
}
 
//=============================================================================================================
 
void ChannelRhiView::setEpochMarkers(const QVector<int>& triggerSamples)
{
    m_epochTriggerSamples = triggerSamples;
    m_overlayDirty = true;
    update();
}
 
//=============================================================================================================
 
void ChannelRhiView::setEpochMarkersVisible(bool visible)
{
    if (m_bShowEpochMarkers == visible)
        return;
    m_bShowEpochMarkers = visible;
    m_overlayDirty = true;
    update();
}
 
//=============================================================================================================
 
void ChannelRhiView::setClippingVisible(bool visible)
{
    if (m_bShowClipping == visible)
        return;
    m_bShowClipping = visible;
    update();
}
 
//=============================================================================================================
 
void ChannelRhiView::setZScoreMode(bool enabled)
{
    if (m_bZScoreMode == enabled)
        return;
    m_bZScoreMode = enabled;
    m_vboDirty = true; // VBO data changes (z-score normalization)
    update();
}
 
//=============================================================================================================
 
void ChannelRhiView::setAnnotations(const QVector<AnnotationSpan>& annotations)
{
    m_annotations = annotations;
    m_overlayDirty = true;
    update();
}
 
//=============================================================================================================
 
void ChannelRhiView::setAnnotationSelectionEnabled(bool enabled)
{
    m_annotationSelectionEnabled = enabled;
}
 
//=============================================================================================================
 
void ChannelRhiView::setEventsVisible(bool visible)
{
    if (m_bShowEvents == visible)
        return;
    m_bShowEvents = visible;
    m_overlayDirty = true;
    update();
}
 
bool ChannelRhiView::eventsVisible() const
{
    return m_bShowEvents;
}
 
//=============================================================================================================
 
void ChannelRhiView::setAnnotationsVisible(bool visible)
{
    if (m_bShowAnnotations == visible)
        return;
    m_bShowAnnotations = visible;
    m_overlayDirty = true;
    update();
}
 
bool ChannelRhiView::annotationsVisible() const
{
    return m_bShowAnnotations;
}
 
//=============================================================================================================
 
int ChannelRhiView::hitTestAnnotationBoundary(int px, bool& isStart) const
{
    for (int i = 0; i < m_annotations.size(); ++i) {
        const float xStart = (static_cast<float>(m_annotations[i].startSample) - m_scrollSample) / m_samplesPerPixel;
        const float xEnd = (static_cast<float>(m_annotations[i].endSample + 1) - m_scrollSample) / m_samplesPerPixel;
 
        if (qAbs(px - static_cast<int>(xStart)) <= kAnnBoundaryHitPx) {
            isStart = true;
            return i;
        }
        if (qAbs(px - static_cast<int>(xEnd)) <= kAnnBoundaryHitPx) {
            isStart = false;
            return i;
        }
    }
    return -1;
}
 
//=============================================================================================================
void ChannelRhiView::initialize(QRhiCommandBuffer* cb)
{
    Q_UNUSED(cb);
    m_pipelineDirty = true;
    m_vboDirty = true;
}
 
//=============================================================================================================
 
void ChannelRhiView::releaseResources()
{
    m_pipeline.reset();
    m_srb.reset();
    m_ubo.reset();
    m_gpuChannels.clear();
    m_pipelineDirty = true;
    m_vboDirty = true;
 
    m_overlayPipeline.reset();
    m_overlaySrb.reset();
    m_overlaySampler.reset();
    m_overlayTex.reset();
    m_overlayVbo.reset();
    m_overlayDirty = true;
}
 
//=============================================================================================================
 
void ChannelRhiView::ensurePipeline(QRhi* rhi, QRhiRenderTarget* target)
{
    if (!m_pipelineDirty)
        return;
 
    m_uboStride = static_cast<int>(
        (52 + rhi->ubufAlignment() - 1) & ~(rhi->ubufAlignment() - 1));
 
    // UBO has one slot per *visible* channel row, not all channels
    // In butterfly mode, we need a slot for EVERY channel (all overlaid)
    int totalCh = totalLogicalChannels();
    int nCh;
    if (m_butterflyMode) {
        nCh = qMin(totalCh, kMaxChannels);
    } else {
        nCh = qMin(m_visibleChannelCount, totalCh - m_firstVisibleChannel);
    }
    nCh = qMax(nCh, 1);
    nCh = qMin(nCh, kMaxChannels);
 
    // ── Uniform buffer ──────────────────────────────────────────────────
    bool uboRecreated = false;
    if (!m_ubo || m_ubo->size() < static_cast<quint32>(nCh * m_uboStride)) {
        m_ubo.reset(rhi->newBuffer(QRhiBuffer::Dynamic,
                                   QRhiBuffer::UniformBuffer,
                                   nCh * m_uboStride));
        m_ubo->create();
        uboRecreated = true;
    }
 
    // ── Shader resource bindings ────────────────────────────────────────
    // Recreate if the UBO pointer changed — SRB holds a raw pointer to the UBO.
    if (!m_srb || uboRecreated) {
        m_srb.reset(rhi->newShaderResourceBindings());
        m_srb->setBindings({QRhiShaderResourceBinding::uniformBufferWithDynamicOffset(
            0,
            QRhiShaderResourceBinding::VertexStage |
                QRhiShaderResourceBinding::FragmentStage,
            m_ubo.get(),
            52 // visible block size for the shader
            )});
        m_srb->create();
    }
 
    // ── Shaders ─────────────────────────────────────────────────────────
    // Resource path matches qt_add_shaders PREFIX + file path (including subdirectory).
    QShader vs = loadShader(QStringLiteral(":/disp/shaders/viewers/helpers/shaders/channeldata.vert.qsb"));
    QShader fs = loadShader(QStringLiteral(":/disp/shaders/viewers/helpers/shaders/channeldata.frag.qsb"));
 
    if (!vs.isValid() || !fs.isValid()) {
        qWarning() << "ChannelRhiView: shaders not found. "
                      "Ensure qt_add_shaders is configured in CMakeLists.";
        return;
    }
 
    // ── Graphics pipeline ───────────────────────────────────────────────
    // Destroy any existing pipeline before creating a new one.
    m_pipeline.reset();
    m_pipeline.reset(rhi->newGraphicsPipeline());
    m_pipeline->setShaderStages({{QRhiShaderStage::Vertex, vs},
                                 {QRhiShaderStage::Fragment, fs}});
 
    QRhiVertexInputLayout il;
    il.setBindings({{2 * sizeof(float)}});                           // stride = vec2
    il.setAttributes({{0, 0, QRhiVertexInputAttribute::Float2, 0}}); // location 0 = vec2
 
    m_pipeline->setVertexInputLayout(il);
    m_pipeline->setShaderResourceBindings(m_srb.get());
    m_pipeline->setRenderPassDescriptor(target->renderPassDescriptor());
    m_pipeline->setTopology(QRhiGraphicsPipeline::LineStrip);
    m_pipeline->setDepthTest(false);
    m_pipeline->setDepthWrite(false);
 
    // Alpha blending for anti-aliased lines (if multisampling is disabled)
    QRhiGraphicsPipeline::TargetBlend blend;
    blend.enable = true;
    blend.srcColor = QRhiGraphicsPipeline::SrcAlpha;
    blend.dstColor = QRhiGraphicsPipeline::OneMinusSrcAlpha;
    blend.srcAlpha = QRhiGraphicsPipeline::One;
    blend.dstAlpha = QRhiGraphicsPipeline::OneMinusSrcAlpha;
    m_pipeline->setTargetBlends({blend});
 
    if (!m_pipeline->create()) {
        qWarning() << "ChannelRhiView: failed to create graphics pipeline";
        m_pipeline.reset();
        return;
    }
 
    m_pipelineDirty = false;
}
 
//=============================================================================================================
 
bool ChannelRhiView::isVboDirty() const
{
    if (!m_model)
        return false;
    float visible = width() * m_samplesPerPixel;
    float margin = m_prefetchFactor * visible;
    return m_vboDirty || m_scrollSample < m_vboWindowFirst + margin || (m_scrollSample + visible) > m_vboWindowLast - margin;
}
 
//=============================================================================================================
 
void ChannelRhiView::rebuildVBOs(QRhi* rhi, QRhiResourceUpdateBatch* batch)
{
    if (!m_model)
        return;
 
    int nCh = totalLogicalChannels();
    int px = width();
    float visible = px * m_samplesPerPixel;
 
    // Prefetch window: [scroll - prefetch*visible, scroll + (1+prefetch)*visible]
    float windowFirst = m_scrollSample - m_prefetchFactor * visible;
    float windowLast = m_scrollSample + (1.f + m_prefetchFactor) * visible;
 
    int iFirst = qMax(static_cast<int>(windowFirst), m_model->firstSample());
    int iLast = qMin(static_cast<int>(windowLast),
                     m_model->firstSample() + m_model->totalSamples());
    if (iFirst >= iLast) {
        m_vboDirty = false;
        return;
    }
 
    m_vboWindowFirst = iFirst;
    m_vboWindowLast = iLast;
 
    // VBOs are indexed by logical (filtered) channel index, not model channel index
    m_gpuChannels.resize(nCh);
 
    // Compute the max vertex count across channels to right-size allocations
    int prefetchedSamples = iLast - iFirst;
    // With decimation, vertices ≤ 2 * px * prefetchFactor * (1 + prefetchFactor)
    // Use a conservative upper bound
    int maxVertices = qMax(prefetchedSamples * 2, 2 * px * 4);
    Q_UNUSED(maxVertices)
 
    for (int logCh = 0; logCh < nCh; ++logCh) {
        int ch = actualChannelAt(logCh); // actual model channel index
        if (ch < 0) {
            m_gpuChannels[logCh].vertexCount = 0;
            continue;
        }
        int vboFirst = 0;
        QVector<float> verts = m_model->decimatedVertices(
            ch, iFirst, iLast, static_cast<int>(prefetchedSamples / m_samplesPerPixel), vboFirst);
 
        if (verts.isEmpty()) {
            m_gpuChannels[logCh].vertexCount = 0;
            continue;
        }
 
        // Z-score normalization: replace raw amplitudes with (y - mean) / std
        if (m_bZScoreMode) {
            int nv = verts.size() / 2;
            if (nv > 1) {
                double sum = 0.0, sumSq = 0.0;
                for (int v = 0; v < nv; ++v) {
                    double a = static_cast<double>(verts[v * 2 + 1]);
                    sum += a;
                    sumSq += a * a;
                }
                float mean = static_cast<float>(sum / nv);
                double var = sumSq / nv - static_cast<double>(mean) * mean;
                float sd = var > 0.0 ? static_cast<float>(qSqrt(var)) : 1.f;
                for (int v = 0; v < nv; ++v)
                    verts[v * 2 + 1] = (verts[v * 2 + 1] - mean) / sd;
            }
        }
 
        int vertexCount = verts.size() / 2; // each vertex is (x, y) = 2 floats
        quint32 byteSize = static_cast<quint32>(verts.size() * sizeof(float));
 
        auto& gd = m_gpuChannels[logCh];
 
        // Re-create buffer if size changed significantly
        if (!gd.vbo || static_cast<quint32>(gd.vbo->size()) < byteSize) {
            gd.vbo.reset(rhi->newBuffer(QRhiBuffer::Dynamic,
                                        QRhiBuffer::VertexBuffer,
                                        byteSize));
            if (!gd.vbo->create()) {
                qWarning() << "ChannelRhiView: VBO create failed for channel" << logCh;
                gd.vertexCount = 0;
                continue;
            }
        }
 
        batch->updateDynamicBuffer(gd.vbo.get(), 0, byteSize,
                                   verts.constData());
        gd.vertexCount = vertexCount;
        gd.vboFirstSample = vboFirst;
    }
 
    m_vboDirty = false;
}
 
//=============================================================================================================
 
void ChannelRhiView::updateUBO(QRhiResourceUpdateBatch* batch)
{
    if (!m_model || !m_ubo)
        return;
 
    int totalCh = totalLogicalChannels();
 
    // ── Butterfly mode: one UBO slot per channel, type-based lane positions ──
    if (m_butterflyMode) {
        const auto groups = butterflyTypeGroups();
        int nLanes = groups.size();
        if (nLanes <= 0)
            return;
 
        // Build channel→lane map
        QHash<int, int> chToLane; // model channel idx → lane index
        for (int g = 0; g < groups.size(); ++g)
            for (int ch : groups[g].channelIndices)
                chToLane[ch] = g;
 
        float vw = static_cast<float>(width());
        float vh = static_cast<float>(height());
        float laneRange = 2.f / nLanes; // NDC height per lane
 
        QVarLengthArray<quint8> buf(m_uboStride, 0);
        int nToUpload = qMin(totalCh, kMaxChannels);
 
        for (int logCh = 0; logCh < nToUpload; ++logCh) {
            int ch = actualChannelAt(logCh);
            memset(buf.data(), 0, m_uboStride);
 
            auto info = (ch >= 0) ? m_model->channelInfo(ch) : ChannelDisplayInfo{};
            bool hideThis = (ch < 0) || (m_hideBadChannels && info.bad);
 
            int lane = chToLane.value(ch, -1);
            if (lane < 0)
                hideThis = true;
 
            QColor col = hideThis ? m_bgColor
                                  : (info.bad ? QColor(200, 60, 60, 180) : info.color);
            float yRng = hideThis ? 0.f : laneRange;
 
            float yCenter = (lane >= 0)
                ? (1.f - laneRange * (lane + 0.5f))
                : 0.f;
 
            float rgba[4] = {
                static_cast<float>(col.redF()),
                static_cast<float>(col.greenF()),
                static_cast<float>(col.blueF()),
                static_cast<float>(col.alphaF())};
 
            auto* d = buf.data();
            writeFloats(d, kUboOffsetColor, rgba, 4);
            writeFloat(d, kUboOffsetFirstSample, static_cast<float>(logCh < static_cast<int>(m_gpuChannels.size()) ? m_gpuChannels[logCh].vboFirstSample : 0));
            writeFloat(d, kUboOffsetScrollSample, m_scrollSample);
            writeFloat(d, kUboOffsetSampPerPixel, m_samplesPerPixel);
            writeFloat(d, kUboOffsetViewWidth, vw);
            writeFloat(d, kUboOffsetViewHeight, vh);
            writeFloat(d, kUboOffsetChannelYCenter, yCenter);
            writeFloat(d, kUboOffsetChannelYRange, yRng);
            writeFloat(d, kUboOffsetAmplitudeMax, m_bZScoreMode ? 4.f : info.amplitudeMax);
            writeFloat(d, kUboOffsetShowClipping, (m_bShowClipping && !info.bad && !m_bZScoreMode) ? 1.f : 0.f);
 
            batch->updateDynamicBuffer(m_ubo.get(),
                                       logCh * m_uboStride,
                                       m_uboStride,
                                       buf.constData());
        }
        return;
    }
 
    // ── Normal mode: one UBO slot per visible row ──
    int firstCh = qBound(0, m_firstVisibleChannel, totalCh);
    int visCnt = qMin(m_visibleChannelCount, totalCh - firstCh);
    int nCh = qMin(visCnt, kMaxChannels);
    if (nCh <= 0)
        return;
 
    float vw = static_cast<float>(width());
    float vh = static_cast<float>(height());
    float laneRange = 2.f / nCh; // NDC height of one visible channel row
 
    QVarLengthArray<quint8> buf(m_uboStride, 0);
 
    for (int i = 0; i < nCh; ++i) {
        int logCh = firstCh + i;         // logical (filtered) index
        int ch = actualChannelAt(logCh); // actual model channel index
        memset(buf.data(), 0, m_uboStride);
 
        auto info = (ch >= 0) ? m_model->channelInfo(ch) : ChannelDisplayInfo{};
        bool hideThis = (ch < 0) || (m_hideBadChannels && info.bad);
        // When hiding: use background colour so no trace is painted
        QColor col = hideThis ? m_bgColor
                              : (info.bad ? QColor(200, 60, 60, 180) : info.color);
        // When hiding bad channel: zero amplitude range → flat invisible line
        float yRng = hideThis ? 0.f : laneRange;
 
        float rgba[4] = {
            static_cast<float>(col.redF()),
            static_cast<float>(col.greenF()),
            static_cast<float>(col.blueF()),
            static_cast<float>(col.alphaF())};
 
        // Visible row i: top at NDC +1, bottom at NDC -1
        float yCenter = 1.f - laneRange * (i + 0.5f);
 
        auto* d = buf.data();
        writeFloats(d, kUboOffsetColor, rgba, 4);
        // VBO indexed by logical channel (logCh), not model channel
        writeFloat(d, kUboOffsetFirstSample, static_cast<float>(logCh < static_cast<int>(m_gpuChannels.size()) ? m_gpuChannels[logCh].vboFirstSample : 0));
        writeFloat(d, kUboOffsetScrollSample, m_scrollSample);
        writeFloat(d, kUboOffsetSampPerPixel, m_samplesPerPixel);
        writeFloat(d, kUboOffsetViewWidth, vw);
        writeFloat(d, kUboOffsetViewHeight, vh);
        writeFloat(d, kUboOffsetChannelYCenter, yCenter);
        writeFloat(d, kUboOffsetChannelYRange, yRng);
        writeFloat(d, kUboOffsetAmplitudeMax, m_bZScoreMode ? 4.f : info.amplitudeMax);
        writeFloat(d, kUboOffsetShowClipping, (m_bShowClipping && !info.bad && !m_bZScoreMode) ? 1.f : 0.f);
 
        // UBO slot i corresponds to visible row i
        batch->updateDynamicBuffer(m_ubo.get(),
                                   i * m_uboStride,
                                   m_uboStride,
                                   buf.constData());
    }
}
 
//=============================================================================================================
// Overlay texture — annotations, events, and epoch markers baked into a QImage.
// Alternating per-second bands are now computed in the fragment shader, so this
// image only needs rebuilding when annotations/events change or when the scroll
// exceeds the prefetch window.
//
// The overlay covers a wider sample range than the viewport (controlled by
// kOverlayPrefetchFactor).  The fragment shader maps screen UVs into this
// wider texture via the OverlayParams UBO.
//=============================================================================================================
 
void ChannelRhiView::rebuildOverlayImage(int logicalWidth, int logicalHeight, qreal devicePixelRatio)
{
    const qreal dpr = qMax(devicePixelRatio, 1.0);
    const int pixelWidth = qMax(1, qRound(logicalWidth * dpr));
    const int pixelHeight = qMax(1, qRound(logicalHeight * dpr));
 
    m_overlayImage = QImage(pixelWidth, pixelHeight, QImage::Format_RGBA8888);
    m_overlayImage.setDevicePixelRatio(dpr);
    m_overlayImage.fill(Qt::transparent);
 
    if (logicalWidth <= 0 || logicalHeight <= 0 || m_sfreq <= 0.f || m_samplesPerPixel <= 0.f) {
        m_overlayDirty = false;
        return;
    }
 
    // The overlay covers m_overlayFirstSample .. m_overlayFirstSample + m_overlayTotalSamples.
    // Map sample positions to pixel X using the overlay's own coordinate system.
    const float overlayFirst = m_overlayFirstSample;
    const float overlayTotal = m_overlayTotalSamples;
    const float overlayPixelsPerSample = (overlayTotal > 0.f)
        ? static_cast<float>(logicalWidth) / overlayTotal
        : 0.f;
 
    QPainter p(&m_overlayImage);
    p.setCompositionMode(QPainter::CompositionMode_SourceOver);
 
    // Note: alternating per-second bands are now computed per-pixel in the
    // fragment shader — no QPainter band rendering here.
 
    // ── Annotation spans ────────────────────────────────────────────
    if (m_bShowAnnotations && !m_annotations.isEmpty()) {
        QFont font = p.font();
        font.setPointSizeF(8.0);
        font.setBold(true);
        p.setFont(font);
 
        for (const AnnotationSpan& annotation : m_annotations) {
            const float xStart = (static_cast<float>(annotation.startSample) - overlayFirst) * overlayPixelsPerSample;
            const float xEnd = (static_cast<float>(annotation.endSample + 1) - overlayFirst) * overlayPixelsPerSample;
            if (xEnd < -2.f || xStart > logicalWidth + 2.f) {
                continue;
            }
 
            const float clippedStart = qBound(0.f, xStart, static_cast<float>(logicalWidth));
            const float clippedEnd = qBound(0.f, xEnd, static_cast<float>(logicalWidth));
            if (clippedEnd <= clippedStart) {
                continue;
            }
 
            QColor fillColor = annotation.color;
            fillColor.setAlpha(48);
            p.fillRect(QRectF(clippedStart, 0.f, clippedEnd - clippedStart, static_cast<float>(logicalHeight)),
                       fillColor);
 
            QColor borderColor = annotation.color;
            borderColor.setAlpha(165);
            p.setPen(QPen(borderColor, 1));
            p.drawLine(QPointF(clippedStart, 0.f), QPointF(clippedStart, static_cast<float>(logicalHeight)));
            p.drawLine(QPointF(clippedEnd, 0.f), QPointF(clippedEnd, static_cast<float>(logicalHeight)));
 
            if (!annotation.label.trimmed().isEmpty()) {
                QString label = annotation.label.trimmed();
                QFontMetrics metrics(font);
                QRect labelRect = metrics.boundingRect(label);
                labelRect.adjust(-6, -2, 6, 2);
                const int labelX = qBound(4,
                                          static_cast<int>(clippedStart) + 4,
                                          qMax(4, logicalWidth - labelRect.width() - 4));
                labelRect.moveTopLeft(QPoint(labelX, 4));
                QColor pillColor = annotation.color;
                pillColor.setAlpha(215);
                p.fillRect(labelRect, pillColor);
                p.setPen(Qt::white);
                p.drawText(labelRect, Qt::AlignCenter, label);
            }
        }
    }
 
    // ── Event / stimulus marker lines ───────────────────────────────
    if (m_bShowEvents && !m_events.isEmpty()) {
        for (const EventMarker& ev : m_events) {
            float xF = (static_cast<float>(ev.sample) - overlayFirst) * overlayPixelsPerSample;
            if (xF < -2.f || xF > logicalWidth + 2.f)
                continue;
            QColor lineColor = ev.color;
            lineColor.setAlpha(180);
            p.setPen(QPen(lineColor, 1));
            p.drawLine(QPointF(xF, 0.f), QPointF(xF, static_cast<float>(logicalHeight)));
        }
    }
 
    // ── Epoch trigger marker lines ──────────────────────────────────
    if (m_bShowEpochMarkers && !m_epochTriggerSamples.isEmpty()) {
        QPen epochPen(QColor(100, 100, 100, 140), 1, Qt::DashLine);
        p.setPen(epochPen);
        for (int trigSample : m_epochTriggerSamples) {
            float xF = (static_cast<float>(trigSample) - overlayFirst) * overlayPixelsPerSample;
            if (xF < -2.f || xF > logicalWidth + 2.f)
                continue;
            p.drawLine(QPointF(xF, 0.f), QPointF(xF, static_cast<float>(logicalHeight)));
        }
    }
 
    m_overlayDirty = false;
}
 
//=============================================================================================================
 
void ChannelRhiView::ensureOverlayPipeline(QRhi* rhi, QRhiRenderTarget* target)
{
    if (m_overlayPipeline)
        return;
 
    // Full-screen quad VBO: (pos.x, pos.y, uv.x, uv.y) per vertex, TriangleStrip.
    // Static — the quad vertices never change (screen-space NDC coordinates).
    // NDC Y+ = top. Image UV Y=0 = top.
    //   NDC(-1,-1)=bottom-left → UV(0,1)
    //   NDC(-1, 1)=top-left    → UV(0,0)
    //   NDC( 1,-1)=bottom-right→ UV(1,1)
    //   NDC( 1, 1)=top-right   → UV(1,0)
    static constexpr float kQuadVerts[] = {
        -1.f,
        -1.f,
        0.f,
        1.f,
        -1.f,
        1.f,
        0.f,
        0.f,
        1.f,
        -1.f,
        1.f,
        1.f,
        1.f,
        1.f,
        1.f,
        0.f,
    };
    static constexpr int kQuadBytes = sizeof(kQuadVerts);
    m_overlayVbo.reset(rhi->newBuffer(QRhiBuffer::Immutable,
                                      QRhiBuffer::VertexBuffer,
                                      kQuadBytes));
    if (!m_overlayVbo->create()) {
        m_overlayVbo.reset();
        return;
    }
 
    // Texture — placeholder 1×1; resized lazily in render() when pw/ph are known.
    m_overlayTex.reset(rhi->newTexture(QRhiTexture::RGBA8, QSize(1, 1)));
    m_overlayTex->create();
 
    m_overlaySampler.reset(rhi->newSampler(
        QRhiSampler::Linear, QRhiSampler::Linear,
        QRhiSampler::None,
        QRhiSampler::ClampToEdge, QRhiSampler::ClampToEdge));
    m_overlaySampler->create();
 
    // UBO for per-frame overlay parameters (binding 2, 8 floats = 32 bytes,
    // aligned to 256 for std140 on all backends).
    static constexpr int kOverlayUboSize = 256;
    m_overlayUbo.reset(rhi->newBuffer(QRhiBuffer::Dynamic,
                                      QRhiBuffer::UniformBuffer,
                                      kOverlayUboSize));
    if (!m_overlayUbo->create()) {
        m_overlayVbo.reset();
        m_overlayUbo.reset();
        return;
    }
 
    // SRB: binding 1 = combined image sampler, binding 2 = overlay UBO
    m_overlaySrb.reset(rhi->newShaderResourceBindings());
    m_overlaySrb->setBindings({QRhiShaderResourceBinding::sampledTexture(
                                   1, QRhiShaderResourceBinding::FragmentStage,
                                   m_overlayTex.get(), m_overlaySampler.get()),
                               QRhiShaderResourceBinding::uniformBuffer(
                                   2, QRhiShaderResourceBinding::FragmentStage,
                                   m_overlayUbo.get())});
    m_overlaySrb->create();
 
    auto loadShader = [](const QString& path) -> QShader {
        QFile f(path);
        if (!f.open(QIODevice::ReadOnly)) {
            qWarning() << "ChannelRhiView: cannot open shader" << path;
            return {};
        }
        return QShader::fromSerialized(f.readAll());
    };
 
    QShader vs = loadShader(QStringLiteral(":/disp/shaders/viewers/helpers/shaders/overlay.vert.qsb"));
    QShader fs = loadShader(QStringLiteral(":/disp/shaders/viewers/helpers/shaders/overlay.frag.qsb"));
    if (!vs.isValid() || !fs.isValid()) {
        m_overlayVbo.reset();
        m_overlayUbo.reset();
        m_overlaySrb.reset();
        m_overlaySampler.reset();
        m_overlayTex.reset();
        return;
    }
 
    m_overlayPipeline.reset(rhi->newGraphicsPipeline());
    QRhiGraphicsPipeline::TargetBlend blend;
    blend.enable = true;
    blend.srcColor = QRhiGraphicsPipeline::SrcAlpha;
    blend.dstColor = QRhiGraphicsPipeline::OneMinusSrcAlpha;
    blend.srcAlpha = QRhiGraphicsPipeline::One;
    blend.dstAlpha = QRhiGraphicsPipeline::OneMinusSrcAlpha;
    m_overlayPipeline->setTargetBlends({blend});
    m_overlayPipeline->setTopology(QRhiGraphicsPipeline::TriangleStrip);
    m_overlayPipeline->setDepthTest(false);
    m_overlayPipeline->setDepthWrite(false);
    m_overlayPipeline->setShaderStages({
        {QRhiShaderStage::Vertex, vs},
        {QRhiShaderStage::Fragment, fs},
    });
 
    QRhiVertexInputLayout inputLayout;
    inputLayout.setBindings({QRhiVertexInputBinding(4 * sizeof(float))});
    inputLayout.setAttributes({QRhiVertexInputAttribute(0, 0, QRhiVertexInputAttribute::Float2, 0),
                               QRhiVertexInputAttribute(0, 1, QRhiVertexInputAttribute::Float2, 2 * sizeof(float))});
    m_overlayPipeline->setVertexInputLayout(inputLayout);
    m_overlayPipeline->setShaderResourceBindings(m_overlaySrb.get());
    m_overlayPipeline->setRenderPassDescriptor(target->renderPassDescriptor());
 
    if (!m_overlayPipeline->create()) {
        qWarning() << "ChannelRhiView: overlay pipeline create failed";
        m_overlayPipeline.reset();
        return;
    }
 
    // The static VBO needs an initial upload.  Since ensureOverlayPipeline()
    // is called from render(), we set a flag and do the upload in the render
    // batch instead.
    m_overlayVboNeedsUpload = true;
}
 
//=============================================================================================================
 
void ChannelRhiView::render(QRhiCommandBuffer* cb)
{
    renderFrame(rhi(), renderTarget(), cb);
}
 
//=============================================================================================================
 
void ChannelRhiView::renderFrame(QRhi* rhi, QRhiRenderTarget* target, QRhiCommandBuffer* cb)
{
    if (!m_model || totalLogicalChannels() == 0) {
        // Clear to background colour only
        QRhiResourceUpdateBatch* u = rhi->nextResourceUpdateBatch();
        QColor bg = m_bgColor;
        cb->beginPass(target, bg, {1.f, 0}, u);
        cb->endPass();
        return;
    }
 
    // ── Ensure GPU resources ─────────────────────────────────────────────
    ensurePipeline(rhi, target);
    if (!m_pipeline) {
        // Pipeline not ready: show RED background so the failure is visible
        QRhiResourceUpdateBatch* u = rhi->nextResourceUpdateBatch();
        cb->beginPass(target, QColor(220, 0, 0), {1.f, 0}, u);
        cb->endPass();
        return;
    }
 
    QSize ps = target->pixelSize();
    const int pw = ps.width();
    const int ph = ps.height();
    const int logicalW = width();
    const int logicalH = height();
    const qreal overlayDpr = (logicalW > 0) ? (static_cast<qreal>(pw) / static_cast<qreal>(logicalW)) : 1.0;
 
    QRhiResourceUpdateBatch* batch = rhi->nextResourceUpdateBatch();
 
    if (isVboDirty())
        rebuildVBOs(rhi, batch);
 
    updateUBO(batch);
 
    // ── Overlay image (annotations + events; bands computed in shader) ──
    ensureOverlayPipeline(rhi, target);
    bool overlayReady = false;
    if (m_overlayPipeline && m_overlayVbo && m_overlayUbo && pw > 0 && ph > 0 && logicalW > 0 && logicalH > 0) {
        // Upload the static quad VBO if it was just created
        if (m_overlayVboNeedsUpload) {
            static constexpr float kQuadVerts[] = {
                -1.f,
                -1.f,
                0.f,
                1.f,
                -1.f,
                1.f,
                0.f,
                0.f,
                1.f,
                -1.f,
                1.f,
                1.f,
                1.f,
                1.f,
                1.f,
                0.f,
            };
            batch->uploadStaticBuffer(m_overlayVbo.get(), 0,
                                      static_cast<quint32>(sizeof(kQuadVerts)), kQuadVerts);
            m_overlayVboNeedsUpload = false;
        }
 
        // Compute the overlay prefetch window (wider than the viewport)
        const float visibleSamples = static_cast<float>(logicalW) * m_samplesPerPixel;
        const float extraSamples = kOverlayPrefetchFactor * visibleSamples;
        const float overlayFirstSample = m_scrollSample - extraSamples;
        const float overlayTotalSamples = visibleSamples + 2.0f * extraSamples;
        // Width of overlay texture in logical pixels = 1 + 2*prefetch factor times viewport
        const int overlayLogicalW = static_cast<int>(std::ceil(
            (1.0f + 2.0f * kOverlayPrefetchFactor) * static_cast<float>(logicalW)));
 
        // Rebuild the overlay QImage if dirty or resized
        const QSize requiredTexSize(qRound(overlayLogicalW * overlayDpr),
                                    qRound(logicalH * overlayDpr));
        if (m_overlayDirty || requiredTexSize != m_overlayTexSize) {
            // Store the sample range covered by this overlay build
            m_overlayFirstSample = overlayFirstSample;
            m_overlayTotalSamples = overlayTotalSamples;
 
            rebuildOverlayImage(overlayLogicalW, logicalH, overlayDpr);
 
            // (Re)create texture at the correct pixel size
            if (requiredTexSize != m_overlayTexSize) {
                m_overlayTex.reset(rhi->newTexture(QRhiTexture::RGBA8, requiredTexSize));
                m_overlayTex->create();
                // Re-create SRB because it references the texture
                m_overlaySrb->setBindings({QRhiShaderResourceBinding::sampledTexture(
                                               1, QRhiShaderResourceBinding::FragmentStage,
                                               m_overlayTex.get(), m_overlaySampler.get()),
                                           QRhiShaderResourceBinding::uniformBuffer(
                                               2, QRhiShaderResourceBinding::FragmentStage,
                                               m_overlayUbo.get())});
                m_overlaySrb->create();
                m_overlayTexSize = requiredTexSize;
            }
            QRhiTextureUploadEntry entry(0, 0, QRhiTextureSubresourceUploadDescription(m_overlayImage));
            batch->uploadTexture(m_overlayTex.get(), entry);
        }
 
        // Upload per-frame overlay UBO (scroll params for shader-computed bands + UV mapping)
        struct OverlayParams
        {
            float scrollSample;
            float samplesPerPixel;
            float viewWidth;
            float sfreq;
            float firstFileSample;
            float gridEnabled;
            float overlayFirstSample;
            float overlayTotalSamples;
        };
        OverlayParams params;
        params.scrollSample = m_scrollSample;
        params.samplesPerPixel = m_samplesPerPixel;
        params.viewWidth = static_cast<float>(logicalW);
        params.sfreq = m_sfreq;
        params.firstFileSample = static_cast<float>(m_firstFileSample);
        params.gridEnabled = m_gridVisible ? 1.0f : 0.0f;
        params.overlayFirstSample = m_overlayFirstSample;
        params.overlayTotalSamples = m_overlayTotalSamples;
        batch->updateDynamicBuffer(m_overlayUbo.get(), 0,
                                   static_cast<quint32>(sizeof(params)), &params);
 
        overlayReady = true;
    }
 
    // ── Render pass ──────────────────────────────────────────────────────
    QColor bg = m_bgColor;
    cb->beginPass(target, bg, {1.f, 0}, batch);
 
    cb->setViewport(QRhiViewport(0.f, 0.f, static_cast<float>(pw),
                                 static_cast<float>(ph)));
 
    // ── Waveform traces ──────────────────────────────────────────────────
    cb->setGraphicsPipeline(m_pipeline.get());
 
    int totalCh = totalLogicalChannels();
 
    if (m_butterflyMode) {
        // Butterfly: render ALL channels; UBO slots indexed by logical channel
        int nToRender = qMin(totalCh, kMaxChannels);
        for (int logCh = 0; logCh < nToRender; ++logCh) {
            if (logCh >= static_cast<int>(m_gpuChannels.size()))
                break;
            auto& gd = m_gpuChannels[logCh];
            if (!gd.vbo || gd.vertexCount < 2)
                continue;
 
            quint32 dynOffset = static_cast<quint32>(logCh * m_uboStride);
            QRhiCommandBuffer::DynamicOffset dynOff{0, dynOffset};
            cb->setShaderResources(m_srb.get(), 1, &dynOff);
 
            QRhiCommandBuffer::VertexInput vi(gd.vbo.get(), 0);
            cb->setVertexInput(0, 1, &vi);
            cb->draw(static_cast<quint32>(gd.vertexCount));
        }
    } else {
        // Normal: render only the visible channel window
        int firstCh = qBound(0, m_firstVisibleChannel, totalCh);
        int visCnt = qMin(m_visibleChannelCount, totalCh - firstCh);
        int nToRender = qMin(visCnt, kMaxChannels);
 
        for (int i = 0; i < nToRender; ++i) {
            int logCh = firstCh + i;
            if (logCh >= static_cast<int>(m_gpuChannels.size()))
                break;
            auto& gd = m_gpuChannels[logCh];
            if (!gd.vbo || gd.vertexCount < 2)
                continue;
 
            quint32 dynOffset = static_cast<quint32>(i * m_uboStride);
            QRhiCommandBuffer::DynamicOffset dynOff{0, dynOffset};
            cb->setShaderResources(m_srb.get(), 1, &dynOff);
 
            QRhiCommandBuffer::VertexInput vi(gd.vbo.get(), 0);
            cb->setVertexInput(0, 1, &vi);
            cb->draw(static_cast<quint32>(gd.vertexCount));
        }
    } // end butterfly/normal branch
 
    // ── Overlay blit (bands + event lines) — drawn after waveforms ───────
    if (overlayReady) {
        cb->setGraphicsPipeline(m_overlayPipeline.get());
        cb->setShaderResources(m_overlaySrb.get());
        QRhiCommandBuffer::VertexInput overlayVi(m_overlayVbo.get(), 0);
        cb->setVertexInput(0, 1, &overlayVi);
        cb->draw(4); // TriangleStrip: 4 vertices = 2 triangles = full-screen quad
    }
 
    cb->endPass();
}
 
void ChannelRhiView::paintEvent(QPaintEvent* event)
{
    QRhiWidget::paintEvent(event);
    drawOverlays();
}
 
//=============================================================================================================
 
QImage ChannelRhiView::renderToImage(const QSize& size) const
{
    const int pw = size.isValid() ? size.width() : width();
    const int ph = size.isValid() ? size.height() : height();
    if (!m_model || pw <= 0 || ph <= 0 || m_samplesPerPixel <= 0.f) {
        return QImage();
    }
 
    // Same rows and horizontal scale as on screen: the time span shown stays the same at any output width
    const float spp = m_samplesPerPixel * static_cast<float>(qMax(width(), 1)) / static_cast<float>(pw);
    const float scrollSample = m_scrollSample;
    const QColor bgColor = m_bgColor;
    const bool gridVisible = m_gridVisible;
    const float sfreq = m_sfreq;
    const int firstFileSample = m_firstFileSample;
    const bool zScoreMode = m_bZScoreMode;
    const bool showClipping = m_bShowClipping;
    const QVector<EventMarker> events = m_bShowEvents ? m_events : QVector<EventMarker>();
    const QVector<AnnotationSpan> annotations = m_bShowAnnotations ? m_annotations : QVector<AnnotationSpan>();
    const QVector<int> epochMarkers = m_bShowEpochMarkers ? m_epochTriggerSamples : QVector<int>();
    const ChannelDataModel* model = m_model.data();
 
    // (model channel, lane) for every trace to draw, laid out exactly like updateUBO()
    QVector<QPair<int, int>> traces;
    int laneCount = 0;
    if (m_butterflyMode) {
        const QVector<ButterflyTypeGroup> groups = butterflyTypeGroups();
        laneCount = static_cast<int>(groups.size());
        for (int lane = 0; lane < laneCount; ++lane) {
            for (int ch : groups[lane].channelIndices) {
                traces.append({ch, lane});
            }
        }
    } else {
        const QVector<int> channelIndices = effectiveChannelIndices();
        const int firstCh = qBound(0, m_firstVisibleChannel, static_cast<int>(channelIndices.size()));
        laneCount = qMin(m_visibleChannelCount, static_cast<int>(channelIndices.size()) - firstCh);
        for (int lane = 0; lane < laneCount; ++lane) {
            traces.append({channelIndices[firstCh + lane], lane});
        }
    }
    if (laneCount <= 0) {
        QImage blank(pw, ph, QImage::Format_RGB32);
        blank.fill(bgColor.rgb());
        return blank;
    }
 
    QImage img(pw, ph, QImage::Format_RGB32);
    img.fill(bgColor.rgb());
 
    QPainter p(&img);
    p.setRenderHint(QPainter::Antialiasing, false);
 
    const float laneH = static_cast<float>(ph) / static_cast<float>(laneCount);
    int firstSample = static_cast<int>(scrollSample);
    int lastSample = firstSample + static_cast<int>(pw * spp) + 1;
 
    // ── Alternating per-second background bands ─────────────────────
    // Draw subtle alternating grey/white bands every second, like MNE-Python browser.
    if (gridVisible && sfreq > 0.f) {
        float samplesPerSec = sfreq;
        float firstBound = std::floor(
                               (scrollSample - static_cast<float>(firstFileSample)) / samplesPerSec) *
                samplesPerSec +
            static_cast<float>(firstFileSample);
 
        // Determine parity of the first band (0 = even, 1 = odd)
        long long bandIndex = static_cast<long long>(
            (firstBound - static_cast<float>(firstFileSample)) / samplesPerSec);
        bool oddBand = (bandIndex & 1) != 0;
 
        // Odd seconds are darkened by 8 %, as in overlay.frag
        const QColor altColor(qRound(bgColor.red() * 0.92),
                              qRound(bgColor.green() * 0.92),
                              qRound(bgColor.blue() * 0.92));
 
        for (float s = firstBound; s < lastSample; s += samplesPerSec, oddBand = !oddBand) {
            if (!oddBand)
                continue; // even seconds use the regular bgColor already filled
            float xStart = (s - scrollSample) / spp;
            float xEnd = xStart + samplesPerSec / spp;
            xStart = qBound(0.f, xStart, static_cast<float>(pw));
            xEnd = qBound(0.f, xEnd, static_cast<float>(pw));
            if (xEnd > xStart)
                p.fillRect(QRectF(xStart, 0, xEnd - xStart, ph), altColor);
        }
    }
 
    // ── Grid pass ──────────────────────────────────────────────────────
    if (gridVisible) {
        for (int i = 0; i < laneCount; ++i) {
            float yMid = (i + 0.5f) * laneH;
            float yTop = i * laneH;
 
            if (i > 0) {
                p.setPen(QPen(QColor(205, 205, 215), 1));
                p.drawLine(QPointF(0, yTop), QPointF(pw, yTop));
            }
 
            QPen guidePen(QColor(228, 228, 235), 1, Qt::DotLine);
            guidePen.setDashPattern({3, 4});
            p.setPen(guidePen);
            p.drawLine(QPointF(0, yMid - laneH * 0.44f), QPointF(pw, yMid - laneH * 0.44f));
            p.drawLine(QPointF(0, yMid + laneH * 0.44f), QPointF(pw, yMid + laneH * 0.44f));
 
            p.setPen(QPen(QColor(210, 210, 218), 1));
            p.drawLine(QPointF(0, yMid), QPointF(pw, yMid));
        }
 
        if (sfreq > 0.f) {
            static const float kNiceIntervals[] = {
                0.05f, 0.1f, 0.2f, 0.5f, 1.f, 2.f, 5.f, 10.f, 30.f, 60.f};
            float pxPerSecond = sfreq / spp;
            float tickIntervalS = kNiceIntervals[0];
            for (float iv : kNiceIntervals) {
                tickIntervalS = iv;
                if (iv * pxPerSecond >= 80.f)
                    break;
            }
            float tickSamples = tickIntervalS * sfreq;
            float origin = static_cast<float>(firstFileSample);
            float firstTick = std::ceil((scrollSample - origin) / tickSamples) * tickSamples + origin;
 
            p.setPen(QPen(QColor(205, 205, 210), 1));
            for (float s = firstTick; s < lastSample; s += tickSamples) {
                float xPx = (s - scrollSample) / spp;
                p.drawLine(QPointF(xPx, 0), QPointF(xPx, ph));
            }
        }
    }
 
    // ── Annotation span pass ────────────────────────────────────────
    if (!annotations.isEmpty()) {
        QFont font = p.font();
        font.setPointSizeF(8.0);
        font.setBold(true);
        p.setFont(font);
 
        for (const AnnotationSpan& annotation : annotations) {
            float xStart = (static_cast<float>(annotation.startSample) - scrollSample) / spp;
            float xEnd = (static_cast<float>(annotation.endSample + 1) - scrollSample) / spp;
 
            if (xEnd < -2.f || xStart > pw + 2.f) {
                continue;
            }
 
            xStart = qBound(0.f, xStart, static_cast<float>(pw));
            xEnd = qBound(0.f, xEnd, static_cast<float>(pw));
            if (xEnd <= xStart) {
                continue;
            }
 
            QColor fillColor = annotation.color;
            fillColor.setAlpha(48);
            p.fillRect(QRectF(xStart, 0.f, xEnd - xStart, static_cast<float>(ph)), fillColor);
 
            QColor borderColor = annotation.color;
            borderColor.setAlpha(165);
            p.setPen(QPen(borderColor, 1));
            p.drawLine(QPointF(xStart, 0.f), QPointF(xStart, static_cast<float>(ph)));
            p.drawLine(QPointF(xEnd, 0.f), QPointF(xEnd, static_cast<float>(ph)));
 
            if (!annotation.label.trimmed().isEmpty()) {
                const QString label = annotation.label.trimmed();
                QFontMetrics metrics(font);
                QRect labelRect = metrics.boundingRect(label);
                labelRect.adjust(-6, -2, 6, 2);
                const int labelX = qBound(4,
                                          static_cast<int>(xStart) + 4,
                                          qMax(4, pw - labelRect.width() - 4));
                labelRect.moveTopLeft(QPoint(labelX, 4));
                QColor pillColor = annotation.color;
                pillColor.setAlpha(215);
                p.fillRect(labelRect, pillColor);
                p.setPen(Qt::white);
                p.drawText(labelRect, Qt::AlignCenter, label);
            }
        }
    }
 
    // ── Channel waveform pass (same mapping as channeldata.vert / .frag) ──
    for (const auto& [ch, lane] : std::as_const(traces)) {
        const ChannelDisplayInfo info = model->channelInfo(ch);
 
        int vboFirst = 0;
        QVector<float> verts = model->decimatedVertices(ch, firstSample, lastSample, pw, vboFirst);
        const int nVerts = static_cast<int>(verts.size() / 2);
        if (nVerts < 2) {
            continue;
        }
 
        // Z-score mode: (y - mean) / std, with ±4 std filling the row like the GPU path
        float offset = 0.f;
        float amplitudeMax = info.amplitudeMax;
        if (zScoreMode) {
            double sum = 0.0;
            double sumSq = 0.0;
            for (int v = 0; v < nVerts; ++v) {
                const double amp = static_cast<double>(verts[v * 2 + 1]);
                sum += amp;
                sumSq += amp * amp;
            }
            const double mean = sum / nVerts;
            const double var = sumSq / nVerts - mean * mean;
            offset = static_cast<float>(mean);
            amplitudeMax = 4.f * (var > 0.0 ? static_cast<float>(qSqrt(var)) : 1.f);
        }
 
        const QPen normalPen(info.bad ? QColor(200, 60, 60, 180) : info.color, 1.2);
        const QPen clipPen(QColor(255, 0, 0), 1.6);
        const bool doClip = showClipping && !info.bad && !zScoreMode;
        const float yMid = (static_cast<float>(lane) + 0.5f) * laneH;
 
        QPolygonF seg;
        seg.reserve(nVerts);
        bool prevClipped = false;
        for (int v = 0; v < nVerts; ++v) {
            const float norm = amplitudeMax > 0.f
                ? qBound(-2.f, (verts[v * 2 + 1] - offset) / amplitudeMax, 2.f)
                : 0.f;
            const QPointF pt((static_cast<float>(vboFirst) + verts[v * 2] - scrollSample) / spp,
                             yMid - norm * 0.45f * laneH);
            const bool clipped = doClip && qAbs(norm) >= 0.95f;
            if (v > 0 && clipped != prevClipped) {
                seg.append(pt);
                p.setPen(prevClipped ? clipPen : normalPen);
                p.drawPolyline(seg);
                seg.clear();
            }
            seg.append(pt);
            prevClipped = clipped;
        }
        if (seg.size() > 1) {
            p.setPen(prevClipped ? clipPen : normalPen);
            p.drawPolyline(seg);
        }
    }
 
    // ── Event / stimulus marker pass ─────────────────────────────────
    // Draw coloured vertical lines spanning the full channel area.
    // Label chips are shown in the TimeRulerWidget stim lane.
    if (!events.isEmpty() && spp > 0.f) {
        for (const EventMarker& ev : events) {
            float xF = (static_cast<float>(ev.sample) - scrollSample) / spp;
            if (xF < -2.f || xF > pw + 2.f)
                continue;
            int ix = static_cast<int>(xF);
 
            QColor lineColor = ev.color;
            lineColor.setAlpha(180);
            p.setPen(QPen(lineColor, 1));
            p.drawLine(ix, 0, ix, ph);
        }
    }
 
    // ── Epoch trigger marker pass ────────────────────────────────────
    // Draw dashed grey vertical lines at epoch trigger positions.
    if (!epochMarkers.isEmpty() && spp > 0.f) {
        QPen epochPen(QColor(100, 100, 100, 140), 1, Qt::DashLine);
        p.setPen(epochPen);
        for (int trigSample : epochMarkers) {
            float xF = (static_cast<float>(trigSample) - scrollSample) / spp;
            if (xF < -2.f || xF > pw + 2.f)
                continue;
            int ix = static_cast<int>(xF);
            p.drawLine(ix, 0, ix, ph);
        }
    }
 
    return img;
}
 
//=============================================================================================================
 
void ChannelRhiView::drawOverlays()
{
    // Schedule an overlay repaint so crosshair/scalebars/ruler stay in sync
    // after GPU-driven scroll/zoom repaints.  Use update() (asynchronous)
    // instead of repaint() because this is called from within paintEvent;
    // synchronous repaint() from inside a paint handler can starve sibling
    // widgets (e.g. the overview bar) of paint cycles.
    if (m_overlay && (m_crosshairEnabled || m_scalebarsVisible || m_rulerActive))
        m_overlay->update();
}
 
//=============================================================================================================
 
static QString formatAmplitude(float amp, const QString& unit)
{
    float absAmp = qAbs(amp);
    if (absAmp == 0.f)
        return QStringLiteral("0 ") + unit;
    if (absAmp < 1e-9f)
        return QString::number(amp * 1e12f, 'f', 1) + QStringLiteral(" p") + unit;
    if (absAmp < 1e-6f)
        return QString::number(amp * 1e9f, 'f', 1) + QStringLiteral(" n") + unit;
    if (absAmp < 1e-3f)
        return QString::number(amp * 1e6f, 'f', 1) + QStringLiteral(" µ") + unit;
    if (absAmp < 1.f)
        return QString::number(amp * 1e3f, 'f', 1) + QStringLiteral(" m") + unit;
    return QString::number(amp, 'f', 3) + QStringLiteral(" ") + unit;
}
 
static QString unitForType(const QString& typeLabel)
{
    if (typeLabel == QStringLiteral("MEG grad"))
        return QStringLiteral("T/m");
    if (typeLabel == QStringLiteral("MEG mag") || typeLabel == QStringLiteral("MEG"))
        return QStringLiteral("T");
    if (typeLabel == QStringLiteral("EEG") ||
        typeLabel == QStringLiteral("EOG") ||
        typeLabel == QStringLiteral("ECG") ||
        typeLabel == QStringLiteral("EMG"))
        return QStringLiteral("V");
    return QStringLiteral("AU");
}
 
//=============================================================================================================
 
void ChannelRhiView::drawCrosshair(QPainter& p)
{
    if (m_crosshairX < 0 || m_crosshairY < 0)
        return;
    if (!m_model || totalLogicalChannels() == 0)
        return;
 
    const int w = width();
    const int h = height();
 
    // Draw crosshair lines
    QPen crossPen(QColor(80, 80, 80, 160), 1, Qt::DashLine);
    p.setPen(crossPen);
    p.drawLine(m_crosshairX, 0, m_crosshairX, h);
    p.drawLine(0, m_crosshairY, w, m_crosshairY);
 
    int sample = static_cast<int>(m_scrollSample + static_cast<float>(m_crosshairX) * m_samplesPerPixel);
    float timeSec = (m_sfreq > 0.f) ? static_cast<float>(sample - m_firstFileSample) / m_sfreq : 0.f;
    QString channelLabel;
    QString unitStr;
    float value = 0.f;
 
    if (m_butterflyMode) {
        // In butterfly mode, lanes correspond to type groups
        const auto groups = butterflyTypeGroups();
        int nLanes = groups.size();
        if (nLanes <= 0)
            return;
        float laneH = static_cast<float>(h) / nLanes;
        int lane = qBound(0, static_cast<int>(m_crosshairY / laneH), nLanes - 1);
        channelLabel = groups[lane].typeLabel;
        unitStr = unitForType(groups[lane].typeLabel);
    } else {
        // Normal mode: determine the channel and sample under the cursor
        int totalCh = totalLogicalChannels();
        int visCnt = qMin(m_visibleChannelCount, totalCh - m_firstVisibleChannel);
        if (visCnt <= 0)
            return;
 
        float laneH = static_cast<float>(h) / visCnt;
        int row = qBound(0, static_cast<int>(m_crosshairY / laneH), visCnt - 1);
        int ch = actualChannelAt(m_firstVisibleChannel + row);
        if (ch < 0)
            return;
 
        auto info = m_model->channelInfo(ch);
        value = m_model->sampleValueAt(ch, sample);
        channelLabel = info.name;
        unitStr = unitForType(info.typeLabel);
    }
 
    // Draw info label near cursor
    QString timeStr;
    if (m_useClockTime && timeSec >= 0.f) {
        int totalMs = static_cast<int>(timeSec * 1000.f + 0.5f);
        int m = totalMs / 60000;
        int sec = (totalMs % 60000) / 1000;
        int ms = totalMs % 1000;
        timeStr = QString("%1:%2.%3")
                      .arg(m, 2, 10, QChar('0'))
                      .arg(sec, 2, 10, QChar('0'))
                      .arg(ms, 3, 10, QChar('0'));
    } else {
        timeStr = QString::number(static_cast<double>(timeSec), 'f', 3) + QStringLiteral(" s");
    }
    QString label = QString("%1  %2  %3")
                        .arg(channelLabel,
                             timeStr,
                             formatAmplitude(value, unitStr));
 
    QFont f = font();
    f.setPointSizeF(8.5);
    p.setFont(f);
    QFontMetrics fm(f);
    QRect labelRect = fm.boundingRect(label);
    int lx = m_crosshairX + 10;
    int ly = m_crosshairY - 10;
    if (lx + labelRect.width() + 8 > w)
        lx = m_crosshairX - labelRect.width() - 18;
    if (ly - labelRect.height() < 4)
        ly = m_crosshairY + labelRect.height() + 6;
    labelRect.moveTopLeft(QPoint(lx, ly - labelRect.height()));
    labelRect.adjust(-4, -2, 4, 2);
    p.fillRect(labelRect, QColor(255, 255, 255, 220));
    p.setPen(QColor(30, 30, 30));
    p.drawText(labelRect, Qt::AlignCenter, label);
}
 
//=============================================================================================================
 
void ChannelRhiView::emitCursorData()
{
    if (m_crosshairX < 0 || m_crosshairY < 0)
        return;
    if (!m_model || totalLogicalChannels() == 0)
        return;
 
    const int h = height();
    int sample = static_cast<int>(m_scrollSample + static_cast<float>(m_crosshairX) * m_samplesPerPixel);
    float timeSec = (m_sfreq > 0.f) ? static_cast<float>(sample - m_firstFileSample) / m_sfreq : 0.f;
 
    if (m_butterflyMode) {
        const auto groups = butterflyTypeGroups();
        int nLanes = groups.size();
        if (nLanes <= 0)
            return;
        float laneH = static_cast<float>(h) / nLanes;
        int lane = qBound(0, static_cast<int>(m_crosshairY / laneH), nLanes - 1);
        emit cursorDataChanged(timeSec, 0.f,
                               groups[lane].typeLabel,
                               unitForType(groups[lane].typeLabel));
    } else {
        int totalCh = totalLogicalChannels();
        int visCnt = qMin(m_visibleChannelCount, totalCh - m_firstVisibleChannel);
        if (visCnt <= 0)
            return;
        float laneH = static_cast<float>(h) / visCnt;
        int row = qBound(0, static_cast<int>(m_crosshairY / laneH), visCnt - 1);
        int ch = actualChannelAt(m_firstVisibleChannel + row);
        if (ch < 0)
            return;
        auto info = m_model->channelInfo(ch);
        float value = m_model->sampleValueAt(ch, sample);
        emit cursorDataChanged(timeSec, value, info.name, unitForType(info.typeLabel));
    }
}
 
//=============================================================================================================
 
void ChannelRhiView::drawScalebars(QPainter& p)
{
    if (!m_model || totalLogicalChannels() == 0)
        return;
 
    int visCnt;
    if (m_butterflyMode) {
        visCnt = butterflyLaneCount();
    } else {
        int totalCh = totalLogicalChannels();
        visCnt = qMin(m_visibleChannelCount, totalCh - m_firstVisibleChannel);
    }
    if (visCnt <= 0)
        return;
 
    float laneH = static_cast<float>(height()) / visCnt;
 
    // Collect unique channel types and their amplitude scales
    QMap<QString, float> typeScales;
    if (m_butterflyMode) {
        const auto groups = butterflyTypeGroups();
        for (const auto& g : groups)
            if (g.amplitudeMax > 0.f)
                typeScales[g.typeLabel] = g.amplitudeMax;
    } else {
        for (int i = 0; i < visCnt; ++i) {
            int ch = actualChannelAt(m_firstVisibleChannel + i);
            if (ch < 0)
                continue;
            auto info = m_model->channelInfo(ch);
            if (!typeScales.contains(info.typeLabel) && info.amplitudeMax > 0.f)
                typeScales[info.typeLabel] = info.amplitudeMax;
        }
    }
 
    if (typeScales.isEmpty())
        return;
 
    QFont f = font();
    f.setPointSizeF(8.0);
    p.setFont(f);
    QFontMetrics fm(f);
 
    // Draw scalebars in the bottom-right corner
    const int margin = 12;
    // amplitudeMax spans 45 % of a row (channeldata.vert); label the amplitude the drawn bar length stands for
    const float scalePx = laneH * 0.45f;
    const int barHeight = qBound(20, qRound(scalePx), 60);
    int x = width() - margin;
    int y = height() - margin;
 
    for (auto it = typeScales.constEnd(); it != typeScales.constBegin();) {
        --it;
        QString unit = unitForType(it.key());
        float ampValue = it.value() * static_cast<float>(barHeight) / scalePx;
        QString label = it.key() + QStringLiteral(": ") + formatAmplitude(ampValue, unit);
 
        int textW = fm.horizontalAdvance(label);
        int barX = x - textW - 14;
 
        // Background pill
        QRect bgRect(barX - 4, y - barHeight - fm.height() - 4, textW + 22, barHeight + fm.height() + 8);
        p.fillRect(bgRect, QColor(255, 255, 255, 200));
 
        // Draw bar
        QPen barPen(QColor(40, 40, 40), 2);
        p.setPen(barPen);
        int barTop = y - barHeight;
        p.drawLine(barX + 4, barTop, barX + 4, y);
        // Tick marks
        p.drawLine(barX, barTop, barX + 8, barTop);
        p.drawLine(barX, y, barX + 8, y);
 
        // Label
        p.setPen(QColor(30, 30, 30));
        p.drawText(barX + 14, y - barHeight / 2 + fm.ascent() / 2, label);
 
        y -= barHeight + fm.height() + 16;
    }
}
 
//=============================================================================================================
 
void ChannelRhiView::drawRulerOverlay(QPainter& p)
{
    int x0 = m_rulerX0, y0 = m_rulerY0;
    int x1 = m_rulerX1, y1 = m_rulerY1;
 
    const bool snapH = (m_rulerSnap == RulerSnap::Horizontal);
    const bool snapV = (m_rulerSnap == RulerSnap::Vertical);
 
    const QColor activeColor(40, 120, 200, 220);
    const QColor dimColor(130, 160, 200, 120);
    int tickLen = 5;
 
    // ── Semi-transparent "frozen" overlay over the measured area ──
    {
        QRect measured;
        if (snapH)
            measured = QRect(QPoint(qMin(x0, x1), 0),
                             QPoint(qMax(x0, x1), height()));
        else if (snapV)
            measured = QRect(QPoint(0, qMin(y0, y1)),
                             QPoint(width(), qMax(y0, y1)));
        else
            measured = QRect(QPoint(qMin(x0, x1), qMin(y0, y1)),
                             QPoint(qMax(x0, x1), qMax(y0, y1)));
        p.fillRect(measured, QColor(255, 255, 255, 60));
        // Subtle border around the measured region
        p.setPen(QPen(QColor(40, 120, 200, 80), 1));
        p.drawRect(measured);
    }
 
    // Vertical guide lines at the two X positions
    QPen vLinePen(snapV ? dimColor : activeColor, 1, Qt::DashLine);
    p.setPen(vLinePen);
    p.drawLine(x0, 0, x0, height());
    if (!snapV)
        p.drawLine(x1, 0, x1, height());
 
    // Horizontal guide lines at the two Y positions (only when vertical snap)
    if (snapV) {
        QPen hGuidePen(activeColor, 1, Qt::DashLine);
        p.setPen(hGuidePen);
        p.drawLine(0, y0, width(), y0);
        p.drawLine(0, y1, width(), y1);
    }
 
    // Horizontal span line at y0
    QPen hLinePen(snapV ? dimColor : activeColor, snapH ? 2 : 1);
    p.setPen(hLinePen);
    if (!snapV)
        p.drawLine(qMin(x0, x1), y0, qMax(x0, x1), y0);
 
    // Vertical span line at x0
    QPen vSpanPen(snapH ? dimColor : activeColor, snapV ? 2 : 1);
    p.setPen(vSpanPen);
    if (!snapH)
        p.drawLine(x0, qMin(y0, y1), x0, qMax(y0, y1));
 
    // End tick marks
    if (!snapV) {
        p.setPen(QPen(activeColor, 1));
        p.drawLine(x0 - tickLen, y0, x0 + tickLen, y0);
        p.drawLine(x1 - tickLen, y0, x1 + tickLen, y0);
    }
    if (!snapH) {
        p.setPen(QPen(activeColor, 1));
        p.drawLine(x0, y0 - tickLen, x0, y0 + tickLen);
        p.drawLine(x0, y1 - tickLen, x0, y1 + tickLen);
    }
 
    // ── Measurement labels ────────────────────────────────────────────
    float deltaSamples = static_cast<float>(x1 - x0) * m_samplesPerPixel;
    float deltaSec = (m_sfreq > 0.f) ? deltaSamples / m_sfreq : 0.f;
 
    float deltaAmp = 0.f;
    QString ampUnit = QStringLiteral("AU");
    if (m_model && totalLogicalChannels() > 0) {
        int totalCh = totalLogicalChannels();
        int visCnt = qMin(m_visibleChannelCount, totalCh - m_firstVisibleChannel);
        if (visCnt > 0) {
            float laneH = static_cast<float>(height()) / visCnt;
            int row = qBound(0, static_cast<int>(y0 / laneH), visCnt - 1);
            int ch = actualChannelAt(m_firstVisibleChannel + row);
            if (ch < 0)
                ch = 0;
            auto info = m_model->channelInfo(ch);
            if (info.amplitudeMax > 0.f) {
                float dyPx = static_cast<float>(y1 - y0);
                float yScale = info.amplitudeMax / (laneH * 0.45f);
                deltaAmp = -dyPx * yScale;
 
                ampUnit = unitForType(info.typeLabel);
            }
        }
    }
 
    auto fmtTime = [](float sec) -> QString {
        float absSec = qAbs(sec);
        if (absSec < 1.f)
            return QString::number(sec * 1000.f, 'f', 1) + QStringLiteral(" ms");
        return QString::number(sec, 'f', 3) + QStringLiteral(" s");
    };
    auto fmtAmp = [](float amp, const QString& unit) -> QString {
        float absAmp = qAbs(amp);
        if (absAmp < 1e-6f)
            return QString::number(amp * 1e9f, 'f', 3) + QStringLiteral(" n") + unit;
        if (absAmp < 1e-3f)
            return QString::number(amp * 1e6f, 'f', 3) + QStringLiteral(" µ") + unit;
        if (absAmp < 1.f)
            return QString::number(amp * 1e3f, 'f', 3) + QStringLiteral(" m") + unit;
        return QString::number(amp, 'f', 3) + QStringLiteral(" ") + unit;
    };
 
    QString timeLabel = QStringLiteral("\u0394T = ") + fmtTime(deltaSec);
    QString ampLabel = QStringLiteral("\u0394A = ") + fmtAmp(deltaAmp, ampUnit);
 
    QFont f = font();
    f.setPointSizeF(9.0);
    f.setBold(true);
    p.setFont(f);
    QFontMetrics fm(f);
 
    // Time label (shown unless vertical snap)
    if (!snapV) {
        int labelX = (x0 + x1) / 2;
        int labelY = y0 - 6;
        if (labelY < 14)
            labelY = y0 + 16;
 
        QRect tRect = fm.boundingRect(timeLabel);
        tRect.moveCenter(QPoint(labelX, labelY));
        tRect.adjust(-4, -2, 4, 2);
        p.fillRect(tRect, QColor(255, 255, 255, 210));
        p.setPen(QColor(20, 80, 160));
        p.drawText(tRect, Qt::AlignCenter, timeLabel);
    }
 
    // Amplitude label (shown unless horizontal snap)
    if (!snapH) {
        int aLabelX = x0 + 8;
        int aLabelY = (y0 + y1) / 2;
        QRect aRect = fm.boundingRect(ampLabel);
        aRect.moveCenter(QPoint(aLabelX + aRect.width() / 2, aLabelY));
        aRect.adjust(-4, -2, 4, 2);
        p.fillRect(aRect, QColor(255, 255, 255, 210));
        p.setPen(QColor(20, 80, 160));
        p.drawText(aRect, Qt::AlignCenter, ampLabel);
    }
}
 
//=============================================================================================================
 
void ChannelRhiView::drawAnnotationSelectionOverlay(QPainter& p)
{
    const int x0 = qMin(m_annSelX0, m_annSelX1);
    const int x1 = qMax(m_annSelX0, m_annSelX1);
    const int h = height();
 
    // Semi-transparent fill matching annotation overlay style
    p.fillRect(QRect(x0, 0, x1 - x0, h), QColor(210, 60, 60, 50));
 
    // Left and right borders
    QPen borderPen(QColor(210, 60, 60, 180), 2);
    p.setPen(borderPen);
    p.drawLine(x0, 0, x0, h);
    p.drawLine(x1, 0, x1, h);
 
    // Duration label pill at the top
    if (m_sfreq > 0.f && m_samplesPerPixel > 0.f) {
        float deltaSamples = static_cast<float>(x1 - x0) * m_samplesPerPixel;
        float deltaSec = deltaSamples / m_sfreq;
        QString label;
        if (deltaSec < 1.f)
            label = QString::number(deltaSec * 1000.f, 'f', 0) + QStringLiteral(" ms");
        else
            label = QString::number(deltaSec, 'f', 2) + QStringLiteral(" s");
 
        QFont f = p.font();
        f.setPointSizeF(8.0);
        f.setBold(true);
        p.setFont(f);
        QFontMetrics fm(f);
        QRect labelRect = fm.boundingRect(label);
        labelRect.adjust(-6, -2, 6, 2);
        labelRect.moveTopLeft(QPoint(x0 + 4, 4));
        p.fillRect(labelRect, QColor(210, 60, 60, 215));
        p.setPen(Qt::white);
        p.drawText(labelRect, Qt::AlignCenter, label);
    }
}
 
//=============================================================================================================
// Shared event handlers
//=============================================================================================================
 
void ChannelRhiView::resizeEvent(QResizeEvent* event)
{
    QRhiWidget::resizeEvent(event);
    m_vboDirty = true;
    m_overlayDirty = true;
    if (m_overlay)
        m_overlay->syncSize();
    emit viewResized(width(), height());
    update();
}
 
//=============================================================================================================
 
void ChannelRhiView::wheelEvent(QWheelEvent* event)
{
    const QPoint delta = event->angleDelta();
 
    if (event->modifiers() & Qt::ControlModifier) {
        // Ctrl + wheel → zoom time axis
        float factor = (delta.y() > 0) ? 0.8f : 1.25f;
        zoomTo(m_samplesPerPixel * factor, 150);
 
    } else if (qAbs(delta.x()) > qAbs(delta.y())) {
        // Predominantly horizontal gesture (trackpad swipe left/right) → scroll time
        if (!m_frozen) {
            float step = width() * m_samplesPerPixel * 0.1f * m_scrollSpeedFactor * (delta.x() > 0 ? -1.f : 1.f);
            scrollBy(step, 100);
        }
 
    } else if (m_wheelScrollsChannels) {
        // Vertical wheel → scroll channels (up = earlier, down = later)
        int channelStep = (delta.y() > 0) ? -1 : 1;
        int maxFirst = qMax(0, totalLogicalChannels() - m_visibleChannelCount);
        setFirstVisibleChannel(qBound(0, m_firstVisibleChannel + channelStep, maxFirst));
    } else {
        // Vertical wheel → scroll time
        if (!m_frozen) {
            float step = width() * m_samplesPerPixel * 0.15f * m_scrollSpeedFactor * (delta.y() > 0 ? -1.f : 1.f);
            scrollBy(step, 100);
        }
    }
 
    event->accept();
}
 
//=============================================================================================================
 
void ChannelRhiView::mousePressEvent(QMouseEvent* event)
{
    // Right-click → annotation range selection (when annotation mode is ON)
    //            → ruler measurement         (when annotation mode is OFF)
    if (event->button() == Qt::RightButton) {
        // Stop any running inertial scroll
        stopScrollAnimations();
 
        if (m_annotationSelectionEnabled) {
            // Annotation mode: right-drag creates a new annotation range
            m_annSelecting = true;
            m_annSelX0 = m_annSelX1 = event->position().toPoint().x();
            if (m_overlay)
                m_overlay->repaint();
        } else {
            // Normal mode: right-drag starts ruler measurement
            m_rulerActive = true;
            m_rulerSnap = RulerSnap::Free;
            m_rulerX0 = m_rulerX1 = m_rulerRawX1 = event->position().toPoint().x();
            m_rulerY0 = m_rulerY1 = m_rulerRawY1 = event->position().toPoint().y();
            if (m_overlay)
                m_overlay->repaint();
        }
        event->accept();
        return;
    }
 
    if (!m_frozen &&
        (event->button() == Qt::MiddleButton ||
         (event->button() == Qt::LeftButton && (event->modifiers() & Qt::AltModifier)))) {
        m_dragging = true;
        m_dragStartX = event->position().toPoint().x();
        m_dragStartScroll = m_scrollSample;
        event->accept();
        return;
    }
    if (event->button() == Qt::LeftButton) {
        // Stop any running inertial scroll
        stopScrollAnimations();
 
        // Check if clicking on an annotation boundary for drag-resize
        if (m_annotationSelectionEnabled && !m_annotations.isEmpty()) {
            bool isStart = false;
            int hitIdx = hitTestAnnotationBoundary(event->position().toPoint().x(), isStart);
            if (hitIdx >= 0) {
                m_annDragging = true;
                m_annDragIndex = hitIdx;
                m_annDragIsStart = isStart;
                event->accept();
                return;
            }
        }
 
        if (m_frozen) {
            // Frozen: clicks still emit sampleClicked but no drag
            float samplePos = m_scrollSample + static_cast<float>(event->position().x()) * m_samplesPerPixel;
            emit sampleClicked(static_cast<int>(samplePos));
            event->accept();
            return;
        }
        // Record start position; activate drag on move (threshold in mouseMoveEvent)
        m_leftButtonDown = true;
        m_leftDragActivated = false;
        m_leftDownX = event->position().toPoint().x();
        m_leftDownScroll = m_scrollSample;
        m_velocityHistory.clear();
        m_dragTimer.start();
        m_velocityHistory.append({m_leftDownX, 0});
        event->accept();
        return;
    }
    QRhiWidget::mousePressEvent(event);
}
 
//=============================================================================================================
 
void ChannelRhiView::mouseMoveEvent(QMouseEvent* event)
{
    // ── Annotation boundary drag-resize ──────────────────────────────
    if (m_annDragging) {
        // Visually update the annotation boundary while dragging
        int newSample = static_cast<int>(m_scrollSample + static_cast<float>(event->position().toPoint().x()) * m_samplesPerPixel);
        newSample = qMax(newSample, m_firstFileSample);
        if (m_lastFileSample >= 0)
            newSample = qMin(newSample, m_lastFileSample);
 
        if (m_annDragIndex >= 0 && m_annDragIndex < m_annotations.size()) {
            if (m_annDragIsStart)
                m_annotations[m_annDragIndex].startSample = newSample;
            else
                m_annotations[m_annDragIndex].endSample = newSample;
            m_overlayDirty = true;
            update();
        }
        event->accept();
        return;
    }
 
    // ── Annotation range selection drag (right-button, annotation mode) ─
    if (m_annSelecting) {
        m_annSelX1 = event->position().toPoint().x();
        if (m_overlay)
            m_overlay->repaint();
        event->accept();
        return;
    }
 
    if (m_rulerActive) {
        m_rulerRawX1 = event->position().toPoint().x();
        m_rulerRawY1 = event->position().toPoint().y();
 
        // Snap logic: if displacement is dominantly horizontal → lock to horizontal,
        // if dominantly vertical → lock to vertical, otherwise free
        int dx = qAbs(m_rulerRawX1 - m_rulerX0);
        int dy = qAbs(m_rulerRawY1 - m_rulerY0);
        const int kSnapThresh = 8; // minimum movement before snapping
        if (dx < kSnapThresh && dy < kSnapThresh) {
            m_rulerSnap = RulerSnap::Free;
        } else if (dx > dy * 2) {
            m_rulerSnap = RulerSnap::Horizontal;
        } else if (dy > dx * 2) {
            m_rulerSnap = RulerSnap::Vertical;
        } else {
            m_rulerSnap = RulerSnap::Free;
        }
 
        // Apply snap
        switch (m_rulerSnap) {
            case RulerSnap::Horizontal:
                m_rulerX1 = m_rulerRawX1;
                m_rulerY1 = m_rulerY0; // lock Y
                break;
            case RulerSnap::Vertical:
                m_rulerX1 = m_rulerX0; // lock X
                m_rulerY1 = m_rulerRawY1;
                break;
            default:
                m_rulerX1 = m_rulerRawX1;
                m_rulerY1 = m_rulerRawY1;
                break;
        }
 
        if (m_overlay)
            m_overlay->repaint();
        event->accept();
        return;
    }
 
    if (m_dragging) {
        int dx = event->position().toPoint().x() - m_dragStartX;
        float newScroll = m_dragStartScroll - static_cast<float>(dx) * m_samplesPerPixel;
        setScrollSample(newScroll);
        event->accept();
        return;
    }
    if (m_leftButtonDown) {
        int x = event->position().toPoint().x();
        int dx = x - m_leftDownX;
        if (!m_leftDragActivated && qAbs(dx) > 5)
            m_leftDragActivated = true;
        if (m_leftDragActivated) {
            float newScroll = m_leftDownScroll - static_cast<float>(dx) * m_samplesPerPixel;
            setScrollSample(newScroll);
 
            // Record velocity sample; keep only the last 100 ms
            qint64 now = m_dragTimer.elapsed();
            m_velocityHistory.append({x, now});
            while (m_velocityHistory.size() > 1 &&
                   now - m_velocityHistory.first().t > 100)
                m_velocityHistory.removeFirst();
 
            event->accept();
            return;
        }
    }
 
    // ── Crosshair tracking (passive mouse tracking without buttons) ──
    if (m_crosshairEnabled) {
        m_crosshairX = event->position().toPoint().x();
        m_crosshairY = event->position().toPoint().y();
        if (m_overlay)
            m_overlay->repaint();
 
        // Emit cursor data signal here (not from drawCrosshair) to keep
        // signal emission out of the paint path and avoid repaint cascades.
        emitCursorData();
    }
 
    // ── Annotation boundary hover cursor ─────────────────────────────
    if (m_annotationSelectionEnabled && !m_annotations.isEmpty()) {
        bool isStart = false;
        int hitIdx = hitTestAnnotationBoundary(event->position().toPoint().x(), isStart);
        if (hitIdx >= 0) {
            if (m_annHoverIndex != hitIdx || m_annHoverIsStart != isStart) {
                m_annHoverIndex = hitIdx;
                m_annHoverIsStart = isStart;
                setCursor(Qt::SizeHorCursor);
            }
        } else if (m_annHoverIndex >= 0) {
            m_annHoverIndex = -1;
            unsetCursor();
        }
    }
 
    QRhiWidget::mouseMoveEvent(event);
}
 
//=============================================================================================================
 
void ChannelRhiView::mouseReleaseEvent(QMouseEvent* event)
{
    // ── Annotation boundary drag-resize completion ───────────────────
    if (m_annDragging && event->button() == Qt::LeftButton) {
        int newSample = static_cast<int>(m_scrollSample + static_cast<float>(event->position().toPoint().x()) * m_samplesPerPixel);
        newSample = qMax(newSample, m_firstFileSample);
        if (m_lastFileSample >= 0)
            newSample = qMin(newSample, m_lastFileSample);
 
        emit annotationBoundaryMoved(m_annDragIndex, m_annDragIsStart, newSample);
        m_annDragging = false;
        m_annDragIndex = -1;
        event->accept();
        return;
    }
 
    // ── Annotation range selection completion (right-button, annotation mode) ─
    if (m_annSelecting && event->button() == Qt::RightButton) {
        m_annSelX1 = event->position().toPoint().x();
        m_annSelecting = false;
        if (m_overlay)
            m_overlay->repaint();
 
        const int x0 = qMin(m_annSelX0, m_annSelX1);
        const int x1 = qMax(m_annSelX0, m_annSelX1);
        if (qAbs(x1 - x0) > 3) {
            int startSample = static_cast<int>(m_scrollSample + static_cast<float>(x0) * m_samplesPerPixel);
            int endSample = static_cast<int>(m_scrollSample + static_cast<float>(x1) * m_samplesPerPixel);
 
            startSample = qMax(startSample, m_firstFileSample);
            if (m_lastFileSample >= 0)
                endSample = qMin(endSample, m_lastFileSample);
 
            if (endSample >= startSample)
                emit sampleRangeSelected(startSample, endSample);
        }
        event->accept();
        return;
    }
 
    if (m_rulerActive && event->button() == Qt::RightButton) {
        m_rulerRawX1 = event->position().toPoint().x();
        m_rulerRawY1 = event->position().toPoint().y();
        // Apply final snap
        switch (m_rulerSnap) {
            case RulerSnap::Horizontal:
                m_rulerX1 = m_rulerRawX1;
                m_rulerY1 = m_rulerY0;
                break;
            case RulerSnap::Vertical:
                m_rulerX1 = m_rulerX0;
                m_rulerY1 = m_rulerRawY1;
                break;
            default:
                m_rulerX1 = m_rulerRawX1;
                m_rulerY1 = m_rulerRawY1;
                break;
        }
        m_rulerActive = false;
        if (m_overlay)
            m_overlay->repaint();
 
        event->accept();
        return;
    }
 
    if (m_dragging && (event->button() == Qt::MiddleButton || event->button() == Qt::LeftButton)) {
        m_dragging = false;
        event->accept();
        return;
    }
    if (event->button() == Qt::LeftButton && m_leftButtonDown) {
        if (!m_leftDragActivated) {
            // Short tap — emit click position, no inertia
            float samplePos = m_leftDownScroll + static_cast<float>(event->position().x()) * m_samplesPerPixel;
            emit sampleClicked(static_cast<int>(samplePos));
        } else {
            // Compute velocity from recent history and launch inertial animation
            if (m_velocityHistory.size() >= 2) {
                auto oldest = m_velocityHistory.first();
                auto newest = m_velocityHistory.last();
                float dt = static_cast<float>(newest.t - oldest.t);
                if (dt > 5.f) {
                    float dx = static_cast<float>(newest.x - oldest.x);
                    // px/ms → samples/ms (positive dx = dragging right = going backward)
                    float velSampPerMs = -(dx / dt) * m_samplesPerPixel;
                    float speed = qAbs(velSampPerMs);
                    if (speed > 0.3f) { // threshold: ~300 samples/s minimum
                        // OutCubic: f'(0) = 3, so travel = v × duration / 3.
                        // Longer duration and distance for a smooth, phone-like glide.
                        float durationMs = qBound(500.f, speed * 1.0f, 5000.f);
                        float targetScroll = m_scrollSample + velSampPerMs * durationMs / 3.f;
                        targetScroll = qMax(targetScroll, static_cast<float>(m_firstFileSample));
 
                        m_pInertialAnim = new QPropertyAnimation(this, "scrollSample", this);
                        m_pInertialAnim->setDuration(static_cast<int>(durationMs));
                        m_pInertialAnim->setEasingCurve(QEasingCurve::OutCubic);
                        m_pInertialAnim->setStartValue(m_scrollSample);
                        m_pInertialAnim->setEndValue(targetScroll);
                        connect(m_pInertialAnim, &QPropertyAnimation::finished, this, [this]() {
                            m_pInertialAnim = nullptr;
                        });
                        m_pInertialAnim->start(QAbstractAnimation::DeleteWhenStopped);
                    }
                }
            }
        }
        m_leftButtonDown = false;
        m_leftDragActivated = false;
        event->accept();
        return;
    }
    QRhiWidget::mouseReleaseEvent(event);
}
 
//=============================================================================================================
 
void ChannelRhiView::mouseDoubleClickEvent(QMouseEvent* event)
{
    if (!m_model || event->button() != Qt::LeftButton) {
        QRhiWidget::mouseDoubleClickEvent(event);
        return;
    }
 
    int totalCh = totalLogicalChannels();
    int visCnt = qMin(m_visibleChannelCount, totalCh - m_firstVisibleChannel);
    if (visCnt <= 0)
        return;
 
    float laneH = static_cast<float>(height()) / visCnt;
    int row = static_cast<int>(event->position().y() / laneH);
    if (row >= 0 && row < visCnt) {
        int ch = actualChannelAt(m_firstVisibleChannel + row);
        if (ch >= 0) {
            auto info = m_model->channelInfo(ch);
            m_model->setChannelBad(ch, !info.bad);
        }
    }
    event->accept();
}