js8call/JS8_Main/SignalMeter.cpp

// Simple bargraph dB meter
// Originally implemented by Edson Pereira PY2SDR
//

#include "SignalMeter.h"
#include "moc_SignalMeter.cpp"
#include <QFontMetrics>
#include <QHBoxLayout>
#include <QLabel>
#include <QPainter>
#include <QPolygon>
#include <QVBoxLayout>
#include <boost/circular_buffer.hpp>

// Meter component, which displays to the right of the scale, as a
// level gauge with a peak hold indicator. Displays green when the
// level is good, yellow when it's too low, red when it's too high.

class SignalMeter::Meter final : public QWidget {
  public:
    static constexpr int MAX = 100;
    static constexpr int LO = 15;
    static constexpr int HI = 85;

    // We handle the peak hold calculation using a circular buffer that
    // always contains the last 10 values; initially, it'll contain 10
    // zeroes. The current meter reading is whatever the last value we
    // put into the buffer was, and the peak hold level is the largest
    // value in the buffer at any moment.

    explicit Meter(QWidget *parent) : QWidget{parent} {}

    QSize sizeHint() const override { return {10, 100}; }

    int last() const { return m_values.back(); }
    int peak() const { return m_peak; }
    int max() const { return m_max; }

    // Caller has provided us with exciting new information. Since GUI
    // components are in general not thread-safe, we don't need to be
    // concerned about locking here; this function can only be called
    // by the setValue() function of the SignalMeter that created us,
    // which is defined as a slot, should that need to be done by a
    // non-GUI thread.
    //
    // This will get called very frequently, often sequentially with
    // identical values, so to avoid needless repaints, we do need to
    // take some care here to ensure that something actually did change
    // such that we'd need to update.

    void setValue(const int value, const int valueMax) {
        auto const oldLast = last();
        auto const oldPeak = peak();
        auto const oldMax = max();

        m_values.push_back(std::clamp(value, 0, MAX));
        m_peak = *std::max_element(m_values.begin(), m_values.end());
        m_max = valueMax;

        if (last() != oldLast || peak() != oldPeak || max() != oldMax)
            update();
    }

  protected:
    // Draw the level bar, which might be of zero height, coloring it
    // appropriately if we're above or below a warning threshold. If
    // our peak level is non-zero, also draw the peak hold indicator.

    void paintEvent(QPaintEvent *) override {
        QPainter p{this};
        p.setPen(Qt::NoPen);

        if (m_max > HI) {
            p.setBrush(Qt::red);
        } else if (m_peak < LO) {
            p.setBrush(Qt::yellow);
        } else {
            p.setBrush(Qt::green);
        }

        auto const target = contentsRect();
        auto const scaled = [&target](auto const value) {
            return QPoint{
                target.left(),
                static_cast<int>(target.top() + target.height() -
                                 value / (double)MAX * target.height())};
        };

        p.drawRect(QRect{scaled(last()), target.bottomRight()});

        if (peak()) {
            p.setBrush(Qt::white);
            p.setRenderHint(QPainter::Antialiasing);
            p.translate(scaled(peak()));
            p.drawPolygon(
                QPolygon{{target.width(), -4}, {target.width(), 4}, {0, 0}});
        }
    }

  private:
    boost::circular_buffer<int> m_values{10};
    int m_peak;
    int m_max;
};

// Scale component, which displays to the left of the meter.

class SignalMeter::Scale final : public QWidget {
  private:
    static constexpr int text_indent = 2;
    static constexpr int tick_length = 4;
    static constexpr std::size_t tick_range = 10;
    static constexpr std::size_t tick_count = Meter::MAX / tick_range;

  public:
    explicit Scale(QWidget *parent) : QWidget{parent} {
        setSizePolicy(QSizePolicy::Minimum, QSizePolicy::MinimumExpanding);
    }

    QSize sizeHint() const override { return minimumSizeHint(); }

    QSize minimumSizeHint() const override {
        QFontMetrics metrics{font(), this};
        return {metrics.horizontalAdvance("00+") + text_indent + tick_length,
                static_cast<int>(metrics.height() * tick_count)};
    }

  protected:
    void paintEvent(QPaintEvent *) override {
        auto const target = contentsRect();
        auto const metrics = QFontMetrics(font(), this);
        auto const margin = metrics.height() / 2;
        auto const offset = metrics.height() / 4;
        auto const span = target.height() - metrics.height();

        QPainter p{this};
        p.setPen(Qt::white);

        p.drawLine(target.right(), target.top() + margin, target.right(),
                   target.bottom() - margin);

        for (std::size_t tick = 0; tick <= tick_count; ++tick) {
            p.save();
            p.translate(target.right() - tick_length,
                        target.top() + margin + tick * span / tick_count);
            p.drawLine(0, 0, tick_length, 0);
            if (tick & 1) {
                auto const text =
                    QString::number(Meter::MAX - tick * tick_range);
                p.drawText(-(text_indent + metrics.horizontalAdvance(text)),
                           offset, text);
            }
            p.restore();
        }
    }
};

// Signal meter implementation; displays as a scaled level meter above
// a level value display.

SignalMeter::SignalMeter(QWidget *parent)
    : QWidget{parent}, m_scale{new Scale{this}}, m_meter{new Meter{this}},
      m_value{new QLabel{this}} {
    auto outer_layout = new QVBoxLayout;
    outer_layout->setSpacing(8);

    auto inner_layout = new QHBoxLayout;
    inner_layout->setContentsMargins(9, 0, 9, 0);
    inner_layout->setSpacing(0);

    auto label_layout = new QHBoxLayout;
    label_layout->setSpacing(4);

    auto const margin = QFontMetrics(m_scale->font(), m_scale).height() / 2;

    m_meter->setContentsMargins(0, margin, 0, margin);
    m_meter->setSizePolicy(QSizePolicy::Minimum, QSizePolicy::Minimum);

    m_value->setAlignment(Qt::AlignRight);

    inner_layout->addWidget(m_scale);
    inner_layout->addWidget(m_meter);

    label_layout->addWidget(m_value);
    label_layout->addWidget(new QLabel("dB", this));

    outer_layout->addLayout(inner_layout);
    outer_layout->addLayout(label_layout);

    setLayout(outer_layout);
}

void SignalMeter::setValue(const float value, const float valueMax) {
    m_meter->setValue(value, valueMax);
    m_value->setText(QString::number(value, 'f', 0));
}