js8call/plotter.cpp

#include "plotter.h"
#include <algorithm>
#include <cmath>
#include <numeric>
#include <type_traits>
#include <utility>
#include <QBitArray>
#include <QDebug>
#include <QLineF>
#include <QMouseEvent>
#include <QPainter>
#include <QPair>
#include <QPen>
#include <QStack>
#include <QToolTip>
#include <QWheelEvent>
#include "commons.h"
#include "moc_plotter.cpp"
#include "DriftingDateTime.h"
#include "JS8Submode.hpp"

extern "C" {
  void flatten(int     size,
               float * data);
}

namespace
{
  // Default epsilon value for RDP point reduction; adjust to taste.

  constexpr qreal RDP_EPSILON = 2.0;

  // 30 meter band: 10.130-10.140 RTTY
  //                10.140-10.150 Packet

  constexpr float BAND_30M_START = 10.13f;
  constexpr float BAND_30M_END   = 10.15f;
  
  // The WSPR range starts at 10.1401 MHz and runs for 200 Hz.

  constexpr float WSPR_START = 10.1401f;
  constexpr int   WSPR_RANGE = 200;

  // FFT bin width, as with NSPS, a constant; see the JT9 documentation
  // for the reasoning behind the values used here, but in short, since
  // NSPS is always 6912, 1500 for nsps2 and 2048 for nfft3 are optimal.

  constexpr float FFT_BIN_WIDTH = 1500.0 / 2048.0;

  // Vertical divisions in the spectrum display.

  constexpr std::size_t VERT_DIVS = 7;

  // Resize debounce interval, in milliseconds; adjust to taste.

  constexpr auto RESIZE_DEBOUNCE_INTERVAL = 100;

  // Band colors, always drawn with a 3-pixel pen.

  constexpr auto BAND_EDGE = QColor{149, 165, 166};  // Gray
  constexpr auto BAND_GOOD = QColor{ 46, 204, 113};  // Green
  constexpr auto BAND_WARN = QColor{241, 196,  15};  // Yellow
  constexpr auto BAND_WSPR = QColor{230, 126,  34};  // Orange

  // Given a floating point value, return the fractional portion of the
  // value e.g., 42.7 -> 0.7.

  template <typename T,
            typename = std::enable_if_t<std::is_floating_point_v<T>>>
  constexpr auto
  fractionalPart(T const v)
  {
    T                    integralPart;
    return std::modf(v, &integralPart);
  }

  // Given the frequency span of the entire viewable plot region, return
  // the frequency span that each division should occupy.

  auto
  freqPerDiv(float const fSpan)
  {
    if (fSpan > 2500) { return 500; }
    if (fSpan > 1000) { return 200; }
    if (fSpan >  500) { return 100; }
    if (fSpan >  250) { return  50; }
    if (fSpan >  100) { return  20; }
                        return  10;
  }

  // We'll typically end up with a ton of points to draw for the spectrum,
  // and some simplification is worthwhile; use the Ramer–Douglas–Peucker
  // algorithm to reduce to a smaller number of points.
  //
  // We'll modify the inbound polygon in place, such that anything we want
  // to keep is at the start of the polygon and anything we want to omit
  // is at the end, returning an iterator to the new end, i.e., the point
  // one past the last point we want to keep.

  auto
  rdp(QPolygonF  & polygon,
       qreal const epsilon = RDP_EPSILON)
  {
    // Prime our array such that all points are initially in play, and
    // prime our stack to consider the full span; run the stack machine
    // until it empties.

    auto array = QBitArray{polygon.size(), true};
    auto stack = QStack<QPair<qsizetype, qsizetype>>{{{qsizetype{0}, polygon.size() - 1}}};

    while (!stack.isEmpty())
    {
      auto const [
        index0,
        indexZ
      ] = stack.pop();

    // Determine the index of the point at the maximum perpendicular
    // distance from a theoretical line drawn between the first and
    // last points in the span we're presently considering.

      auto const & line0 = polygon.at(index0);
      auto const & lineZ = polygon.at(indexZ);
      auto const   lineX = lineZ.x() - line0.x();
      auto const   lineY = lineZ.y() - line0.y();
      auto const   lineL = std::sqrt(std::pow(lineX, 2) +
                                     std::pow(lineY, 2));

      auto  index  = index0;
      qreal dMax   = 0.0;

      for (auto i = index0 + 1;
                i < indexZ;
              ++i)
      {
        if (array.testBit(i))
        {
          auto const & point = polygon.at(i);
          auto const   d     = std::abs(lineX * (line0.y() - point.y())  -
                                        lineY * (line0.x() - point.x())) /
                                        lineL;
          if (d > dMax)
          {
            index = i;
            dMax  = d;
          }
        }
      }

      // If the max distance is above epsilon, then we have to keep
      // working the problem. If not, cull the indices of points that
      // are not relevant to the result, i.e., everything but for the
      // first and last.

      if (dMax > epsilon)
      {
        stack.push({index0, index});
        stack.push({index, indexZ});
      }
      else
      {
        for (auto i = index0 + 1;
                  i < indexZ;
                ++i)
        {
          array.clearBit(i);
        }
      }
	  }

    // Our array now contains bits set to true for every point that
    // should be kept, false for those that should be removed.

    auto const last  = polygon.end();
    auto       first = polygon.begin();
    qsizetype  i     = 0;

    // Position the iterator at the first point that should be removed.

    for (; first != last && array.testBit(i++); ++first);

    // Which might be nothing at all, in which case we're done here.
    // Otherwise, shift things to be kept forward, preserving order.

    if (first != last)
    {
      auto it = first; while (++it != last)
      {
        if (array.testBit(i++)) *first++ = std::move(*it);
      }
    }

    // We're now pointing to the first element of junk, and all the stuff
    // we want to keep is ahead of it. Return the iterator to our caller.

    return first;
  }

  // Standard overload template for use in visitation.

  template<typename... Ts>
  struct overload : Ts ... { 
      using Ts::operator() ...;
  };

  // While C++20 can deduce the above, C++17 can't; this guide
  // can be removed when we move to C++20 as a requirement.

  template<typename... Ts> overload(Ts...) -> overload<Ts...>;
}

CPlotter::CPlotter(QWidget * parent)
  : QWidget        {parent}
  , m_resize       {new QTimer(this)}
  , m_freqPerPixel {m_binsPerPixel * FFT_BIN_WIDTH}
{
  setFocusPolicy(Qt::StrongFocus);
  setMouseTracking(true);

  // Debounce resize events such that resize() doesn't actually get called
  // until the debounce time has elapsed without any further resize events.

  m_resize->setSingleShot(true);
  m_resize->setInterval(RESIZE_DEBOUNCE_INTERVAL);
  
  connect(m_resize, &QTimer::timeout, this, &CPlotter::resize);
}

QSize
CPlotter::minimumSizeHint() const
{
  return QSize(50, 50);
}

QSize
CPlotter::sizeHint() const
{
  return QSize(180, 180);
}

void
CPlotter::paintEvent(QPaintEvent *)
{
  QPainter p(this);

  p.drawPixmap(0, 0,    m_ScalePixmap);
  p.drawPixmap(0, 30,   m_WaterfallPixmap);
  p.drawPixmap(0, m_h1, m_SpectrumPixmap);

  p.drawPixmap(xFromFreq(m_freq), 30, m_DialPixmap[0]);

  if (m_lastMouseX >= 0)
  {
    p.drawPixmap(m_lastMouseX, 30, m_DialPixmap[1]);
  }

  if (m_filterEnabled && m_filterWidth > 0)
  {
    p.drawPixmap(                                                      0, 0, m_FilterPixmap[0]);
    p.drawPixmap(m_w - m_FilterPixmap[1].deviceIndependentSize().width(), 0, m_FilterPixmap[1]);
  }
}

void
CPlotter::resizeEvent(QResizeEvent *)
{
  m_resize->start();
}

void
CPlotter::drawLine(QString const & text)
{
  m_WaterfallPixmap.scroll(0, 1, m_WaterfallPixmap.rect());

  QPainter p(&m_WaterfallPixmap);

  // Draw a green line across the complete span.

  p.setPen(Qt::green);
  p.drawLine(0, 0, m_w, 0);

  // Compute the number of lines required before we need to draw the
  // text, and note the text to draw, saving it against a potential
  // replot request.

  m_text = text;
  m_line = p.fontMetrics().height() * devicePixelRatio();
  m_replot.push_front(m_text);

  update();
}

void
CPlotter::drawData(WF::SWide swide)
{
  m_WaterfallPixmap.scroll(0, 1, m_WaterfallPixmap.rect());

  QPainter p(&m_WaterfallPixmap);

  // Convert the power scale we receive to dB. Note that while we could
  // convert only m_w elements here for immediate display, we want to
  // convert the full range of the data so that we can be resized and
  // still properly display without having to process the data again.

  std::transform(swide.begin(),
                 swide.end(),
                 swide.begin(),
                 [](auto const value)
                 {
                   return 10.0f * std::log10(value);
                 });

  // Same deal for flattening; full range.

  if (m_flatten) flatten(swide.size(),
                         swide.data());

  // Display the processed data in the waterfall, drawing only the range
  // that's displayed.

  auto       it   = swide.begin();
  auto const end  = it + m_w;
  auto const gain = gainFactor();
  
  for (auto x = 0; it != end; ++it, ++x)
  {
    p.setPen(m_colors[std::clamp(m_plotZero + static_cast<int>(*it * gain), 0, 254)]);
    p.drawPoint(x, 0);
  }

  // See if we've reached the point where we should draw previously computed
  // line text.

  if (--m_line == 0)
  {
    m_line = std::numeric_limits<int>::max();

    p.setPen(Qt::white);
    p.drawText(5, p.fontMetrics().ascent(), m_text);
  }

  // Our spectrum might be of zero height, in which case our overlay pixmap
  // isn't going to be usable; proceed to spectrum work only if it's usable.

  if (!m_OverlayPixmap.isNull())
  {
    // We draw the spectrum by copying the overlay prototype and drawing our
    // points into it.

    m_SpectrumPixmap = m_OverlayPixmap.copy();

    QPainter p(&m_SpectrumPixmap);

    // Add a point to the polyline, where x is the x coordinate, y is the
    // computed value for y, and a is any adjustment that should be made.

    auto const addPoint = [this,
                           gain = std::pow(10.0f, 0.02f * m_plot2dGain),
                           view = m_h2 *  0.9f,
                           span = m_h2 / 70.0f](int   const x,
                                                float const y,
                                                int   const a = 0)
    {
      m_points.emplace_back(x, view - span * ((m_plot2dZero + gain * y) + a));
    };

    // Given an interator pointing to the first element of adjunct summary
    // data, return an iterator indicating where iteration should start.

    auto const getStart = [this](auto const it)
    {
      return it + static_cast<int>(m_startFreq / FFT_BIN_WIDTH + 0.5f);
    };

    // Clear the current points and ensure space exists to add all the
    // points we require without reallocation.

    m_points.clear();
    m_points.reserve(m_w);

    auto it = swide.begin();
    auto x  = 0;

    switch (m_spectrum)
    {
      case Spectrum::Current:
      {
        p.setPen(Qt::green);

        auto const add = m_flatten ? 0 : 15;
        auto const min = *std::min_element(it, end);

        for (; it != end; ++it, ++x) addPoint(x, *it - min, add);
      }
      break;

      case Spectrum::Cumulative:
      {
        p.setPen(Qt::cyan);

        auto const add = m_flatten ? 15 : 30;
        auto       sit = getStart(std::begin(dec_data.savg));

        for (; it != end; ++it, ++x, sit += m_binsPerPixel)
        {
          addPoint(x, std::reduce(sit,
                                  sit + m_binsPerPixel,
                                  0.0f,
                                  [](auto const total,
                                     auto const value)
                                  {
                                    return total + 10.0f * std::log10(value);
                                  }) / m_binsPerPixel, add);
        }
      }
      break;
      
      case Spectrum::LinearAvg:
      {
        p.setPen(Qt::yellow);

        auto sit = getStart(std::begin(spectra_.syellow));

        for (; it != end; ++it, ++x, sit += m_binsPerPixel)
        {
          addPoint(x, std::reduce(sit, sit + m_binsPerPixel) / m_binsPerPixel);
        }
      }
      break;
    }

    // Draw the spectrum line, reducing the resulting points prior to
    // drawing them, but keeping the collection capacity.

    m_points.erase(rdp(m_points), m_points.end());
    p.setRenderHint(QPainter::Antialiasing);
    p.drawPolyline(m_points);
  }

  // Save the data against a potential replot requirement.
  
  m_replot.push_front(std::move(swide));

  update();
}

void
CPlotter::drawDecodeLine(QColor const & color,
                         int    const   ia,
                         int    const   ib)
{
  auto const x1 = xFromFreq(ia);
  auto const x2 = xFromFreq(ib);

  QPainter p(&m_WaterfallPixmap);
  
  p.setPen(color);
  p.drawLine(qMin(x1, x2), 4, qMax(x1, x2), 4);
  p.drawLine(qMin(x1, x2), 0, qMin(x1, x2), 9);
  p.drawLine(qMax(x1, x2), 0, qMax(x1, x2), 9);
}

void
CPlotter::drawHorizontalLine(QColor const & color,
                             int    const   x,
                             int    const   width)
{
  QPainter p(&m_WaterfallPixmap);

  p.setPen(color);
  p.drawLine(x, 0, width <= 0 ? m_w : x + width, 0);
}

void
CPlotter::drawMetrics()
{
  if (m_ScalePixmap.isNull()) return;

  m_ScalePixmap.fill(Qt::white);

  QPainter p(&m_ScalePixmap);

  p.setPen(Qt::black);
  p.drawRect(0, 0, m_w, 30);

  auto        const fSpan   = m_w * m_freqPerPixel;
  auto        const fpd     = freqPerDiv(fSpan);
  float       const ppdV    = fpd / m_freqPerPixel;
  std::size_t const hdivs   = fSpan / fpd + 1.9999f;
  int         const fOffset = ((m_startFreq + fpd - 1) / fpd) * fpd;
  auto        const xOffset = float(fOffset - m_startFreq) / fpd;
  std::size_t const nMajor  = hdivs - 1;
  std::size_t const nMinor  = fpd == 200 ? 4: 5;
  float       const ppdVM   = ppdV / nMinor;
  float       const ppdVL   = ppdV / 2;

  // Draw ticks and labels.

  for (std::size_t iMajor = 0; iMajor < nMajor; iMajor++)
  {
    auto const rMajor = (xOffset + iMajor) * ppdV;
    auto const xMajor = static_cast<int>(rMajor);
    p.drawLine(xMajor, 18, xMajor, 30);

    for (std::size_t iMinor = 1; iMinor < nMinor; iMinor++)
    {
      auto const xMinor = static_cast<int>(rMajor + iMinor * ppdVM);
      p.drawLine(xMinor, 22, xMinor, 30);
    }

    if (xMajor > 70)
    {
       p.drawText(QRect(xMajor - static_cast<int>(ppdVL), 0, static_cast<int>(ppdV), 20),
                  Qt::AlignCenter,
                  QString::number(fOffset + iMajor * fpd));
    }
  }

  // Given a starting frequency and range to cover, return corresponding
  // X values for the sub-band.

  auto const bandX = [this](float const start,
                            int   const range)
  {
    return std::make_pair(xFromFreq(start),
                          xFromFreq(start + range));
  };

  // Given a pair of X values, draw a band line, if visible.

  auto const drawBand = [this, &p](auto const & bandX)
  {
    auto const [x1, x2] = bandX;

    if (x1 <= m_w && x2 > 0)
    {
      p.drawLine(x1 + 1, 26, x2 - 2, 26);
      p.drawLine(x1 + 1, 28, x2 - 2, 28);
    }
  };

  // Colorize the JS8 sub-bands.

  p.setPen(QPen(BAND_EDGE, 3)); drawBand(bandX(   0.0f, 4000));
  p.setPen(QPen(BAND_WARN, 3)); drawBand(bandX( 500.0f, 2500));
  p.setPen(QPen(BAND_GOOD, 3)); drawBand(bandX(1000.0f, 1500));

  // If we're in the 30 meter band, we'd rather that the WSPR sub-band not
  // get stomped on; draw an orange indicator in the scale to denote the
  // WSPR portion of the band.
  //
  // Note that given the way XfromFreq() works, we're always going to see
  // clamped X values here, either 0 or m_w, if the frequency is outside
  // of the range, so we're always going to draw. If the WSPR range is not
  // in the displayed range, the effect will be, given the pen size, that
  // an orange indicator will indicate in which direction the WSPR range
  // lies.

  if (in30MBand())
  {
    auto const wspr = bandX(1.0e6f * (WSPR_START - m_dialFreq), WSPR_RANGE);
    auto       font = QFont();

    font.setBold(true);
    font.setPointSize(10);

    p.setFont(font);
    p.setPen(QPen(BAND_WSPR, 3));
    drawBand(wspr);
    p.drawText(QRect(wspr.first, 0, wspr.second - wspr.first, 25),
               Qt::AlignHCenter|Qt::AlignBottom,
               "WSPR");
  }

  // Our spectrum might be of zero height, in which case our overlay pixmap
  // isn't going to be usable; proceed only if it's usable.

  if (!m_OverlayPixmap.isNull())
  {
    QLinearGradient gradient(0, 0, 0, m_h2);

    gradient.setColorAt(1, Qt::black);
    gradient.setColorAt(0, Qt::darkBlue);

    QPainter p(&m_OverlayPixmap);

    p.setBrush(gradient);
    p.drawRect(0, 0, m_w, m_h2);
    p.setBrush(Qt::SolidPattern);
    p.setPen(QPen(Qt::darkGray, 1, Qt::DotLine));

    // Draw vertical grids.

    auto const x0 = static_cast<int>(fractionalPart((float)m_startFreq / fpd) * ppdV + 0.5f);

    for (std::size_t i = 1; i < hdivs; i++)
    {
      if (auto const x  = static_cast<int>(i * ppdV) - x0;
                    x >= 0 &&
                    x <= m_w)
      {
        p.drawLine(x, 0, x , m_h2);
      }
    }

    // Draw horizontal grids.
    
    float const ppdH = (float)m_h2 / VERT_DIVS; 

    for (std::size_t i = 1; i < VERT_DIVS; i++)
    {
      auto const y = static_cast<int>(i * ppdH);
      p.drawLine(0, y, m_w, y);
    }
  }
}

// Draw the filter overlay pixmaps, if the filter is enabled and has a width
// greater than zero. Note that we could be more clever here and ensure the
// filter is actually visible prior to painting, but what we're doing here
// is reasonably trivial, so probably not worth the effort.

void
CPlotter::drawFilter()
{
  if (m_filterEnabled && m_filterWidth > 0 && !size().isEmpty())
  {
    auto const filterPixmap = [height = size().height(),
                               fill   = QColor(0, 0, 0, std::clamp(m_filterOpacity, 0, 255)),
                               dpr    = devicePixelRatio()](int const width,
                                                            int const lineX)
    {
      // Ending up with an unusable size here is expected, as in the case
      // where the combination of the filter center and width shifts one
      // or both ends of the filter out of the displayed range. Thus, no
      // matter what, we're going to return a pixmap here, though it may
      // be an empty one.

      if (auto const size = QSize(width, height);
                     size.isEmpty())
      {
        return QPixmap();
      }
      else
      {
        QPixmap pixmap = QPixmap(size * dpr);
        pixmap.setDevicePixelRatio(dpr);
        pixmap.fill(fill);

        QPainter p(&pixmap);

        p.setPen(Qt::yellow);
        p.drawLine(lineX, 1, lineX, height);

        return pixmap;
      }
    };

    auto const width = m_filterWidth / 2.0f;
    auto const start = xFromFreq(m_filterCenter - width);
    auto const end   = xFromFreq(m_filterCenter + width);

    m_FilterPixmap = {
      filterPixmap(start, start),
      filterPixmap(size().width() - end, 0)
    };
  }
}

// Draw the two dials, the first of which will be used to display the selected
// offset and bandwith, the second prospective offset and bandwidth. These are
// not reliant on anything but height, submode, and bins per pixel.

void
CPlotter::drawDials()
{
  if (auto const height = size().height() - 30;
                 height > 0)
  {
    auto const width      = static_cast<int>(JS8::Submode::bandwidth(m_nSubMode) / m_freqPerPixel + 0.5f);
    auto const dialPixmap = [size = QSize(width, height),
                             rect = QRect(1, 1, width - 2, height - 2),
                             dpr  = devicePixelRatio()](QColor const & color,
                                                        QBrush const & brush)
    {
      QPixmap pixmap = QPixmap(size * dpr);
      pixmap.setDevicePixelRatio(dpr);
      pixmap.fill(Qt::transparent);

      QPainter p(&pixmap);

      p.setBrush(brush);
      p.setPen(QPen(QBrush(color), 2, Qt::SolidLine, Qt::SquareCap, Qt::MiterJoin));
      p.drawRect(rect);

      return pixmap;
    };

    m_DialPixmap = {
      dialPixmap(Qt::red,   QBrush(QColor(255, 255, 255, 75), Qt::Dense4Pattern)),
      dialPixmap(Qt::white, Qt::transparent)
    };
  }
}

// Replot the waterfall display, using the data present in the replot
// buffer, if any.

void
CPlotter::replot()
{
  if (m_WaterfallPixmap.isNull()) return;

  // Whack anything currently in the waterfall pixmap; we must do this
  // before attaching a painter.

  m_WaterfallPixmap.fill(Qt::black);

  // Given a value, return color a to use for a point, based on the
  // zero, gain, and color palette settings.

  auto const color = [this,
                      gain = gainFactor()](auto const value)
  {
    return m_colors[std::clamp(m_plotZero + static_cast<int>(gain * value), 0, 254)];
  };

  // We need to consider that entries have been added to the replot
  // buffer at a rate proportional to the display pixel ratio, i.e.,
  // it deals in device pixels, not logical pixels, so we must deal
  // with scaling in the y dimension for this to work out.

  QPainter p(&m_WaterfallPixmap);

  p.scale(1, 1 / m_WaterfallPixmap.devicePixelRatio());

  auto y = 0;
  auto o = overload
  {
    // Null drawing; a monostate is constructed as the default when we
    // resize but have no backing data. Nothing to do here; just data
    // that we didn't have when we were resized.

    [](std::monostate const &){},

    // Line drawing; draw the usual green line across the width of the
    // pixmap, annotated by the text provided.

    [ratio = m_WaterfallPixmap.devicePixelRatio(),
     width = m_WaterfallPixmap.size().width(),
     extra = p.fontMetrics().descent(),
     &y    = std::as_const(y),
     &p
    ](QString const & text)
    {
      p.setPen(Qt::white);
      p.save();
      p.scale(1, ratio);
      p.drawText(5, y / ratio - extra, text);
      p.restore();
      p.setPen(Qt::green);
      p.drawLine(0, y, width, y);
    },

    // Standard waterfall data display; run through the vector of data
    // and color each corresponding point in the pixmap appropriately.

    [width  = m_WaterfallPixmap.size().width(),
     &color = std::as_const(color),
     &y     = std::as_const(y),
     &p
    ](WF::SWide const & swide)
    {
      auto       x   = 0;
      auto       it  = swide.begin();
      auto const end = it + width;
      for (; it != end; ++it)
      {
        p.setPen(color(*it));
        p.drawPoint(x, y);
        x++;
      }
    }
  };

  // Our draw routine pushed entries to the front of the buffer, so we
  // can iterate in forward order here, the Qt coordinate system having
  // (0, 0) as the upper-left point.

  for (auto && v : m_replot)
  {
    std::visit(o, v);
    y++;
  }

  // The waterfall pixmap should now look as it did before, but with the
  // current zero, gain, and color palette applied; schedule a repaint.

  update();
}

// Called (indirectly, debounced) from our resize event handler and from
// setPercent2DScreen() after a change to the 2D screen percentage.

void
CPlotter::resize()
{
  if (size().isValid())
  {
    auto const makePixmap = [dpr = devicePixelRatio()](QSize  const & size,
                                                       QColor const & fill)
    {
      auto pixmap = QPixmap(size * dpr);
      
      pixmap.setDevicePixelRatio(dpr);
      pixmap.fill(fill);

      return pixmap;
    };

    m_w  = size().width();
    m_h2 = m_percent2DScreen * (size().height() - 30) / 100.0;
    m_h1 =                      size().height() - m_h2;

    // We want our 3 main pixmaps sized to occupy our entire height,
    // and to be completely filled with an opaque color, since we're
    // going to take the opaque paint even optimization path. If this
    // is a high-DPI display, scale the pixmaps to avoid text looking
    // pixelated.

    m_ScalePixmap     = makePixmap({m_w,   30}, Qt::white);
    m_WaterfallPixmap = makePixmap({m_w, m_h1}, Qt::black);
    m_OverlayPixmap   = makePixmap({m_w, m_h2}, Qt::black);

    // The replot circular buffer should have capacity to hold the full
    // height of the waterfall pixmap, in device, not logical, pixels.
    // Since our variant lists std::monostate as the first alternative,
    // if we get larger here, the added items will be constructed using
    // std::monostate as the alternative.

    m_replot.resize(m_WaterfallPixmap.size().height());

    // The dials, filter, scale and overlay pixmaps don't depend on
    // inbound data, so we can draw them now.

    drawDials();
    drawFilter();
    drawMetrics();

    // The overlay pixmap acts as a prototype for the spectrum pixmap;
    // each time we draw the spectrum, we do so by first making a copy
    // of the overlay, then drawing the spectrum line into it.

    m_SpectrumPixmap = m_OverlayPixmap.copy();

    replot();
  }
}

bool
CPlotter::in30MBand() const
{
  return (m_dialFreq >= BAND_30M_START &&
          m_dialFreq <= BAND_30M_END);
}

int
CPlotter::xFromFreq(float const f) const
{
  return std::clamp(static_cast<int>((f - m_startFreq) / m_freqPerPixel + 0.5f), 0, m_w);
}

float
CPlotter::freqFromX(int const x) const
{
  return m_startFreq + x * m_freqPerPixel;
}

float
CPlotter::gainFactor() const
{
  return 10.f * std::sqrt(m_binsPerPixel * m_waterfallAvg / 15.0f)
              * std::pow(10.0f, 0.015f * m_plotGain); 
}

void
CPlotter::leaveEvent(QEvent * event)
{
  m_lastMouseX = -1;
  event->ignore();
}

void
CPlotter::wheelEvent(QWheelEvent * event)
{
    auto const y = event->angleDelta().y();

    if (auto const d = ((y > 0) - (y < 0)))
    {
      emit changeFreq(event->modifiers() & Qt::ControlModifier
                    ? freq()           + d
                    : freq() / 10 * 10 + d * 10);
    }
    else
    {
      event->ignore();
    }
}

void
CPlotter::mouseMoveEvent(QMouseEvent * event)
{
  m_lastMouseX = std::clamp(static_cast<int>(event->position().x()), 0, m_w);

  update();
  event->ignore();

  QToolTip::showText(event->globalPosition().toPoint(),
                     QString::number(static_cast<int>(freqFromX(m_lastMouseX))));
}

void
CPlotter::mouseReleaseEvent(QMouseEvent * event)
{
  if (Qt::LeftButton == event->button())
  {
    emit changeFreq(static_cast<int>(freqFromX(m_lastMouseX)));
  }
  else
  {
    event->ignore();
  }
}

void
CPlotter::setBinsPerPixel(int const binsPerPixel)
{
  if (m_binsPerPixel != binsPerPixel)
  {
    m_binsPerPixel = std::max(1, binsPerPixel);
    m_freqPerPixel = m_binsPerPixel * FFT_BIN_WIDTH;
    drawMetrics();
    drawFilter();
    drawDials();
    update();
  }
}

void
CPlotter::setColors(Colors const & colors)
{
  if (m_colors != colors)
  {
    m_colors = colors;
    replot();
  }
}

void
CPlotter::setDialFreq(float const dialFreq)
{
  if (m_dialFreq != dialFreq)
  {
    m_dialFreq = dialFreq;
    drawMetrics();
    update();
  }
}

void
CPlotter::setFilter(int const filterCenter,
                    int const filterWidth)
{
  if (m_filterCenter != filterCenter ||
      m_filterWidth  != filterWidth)
  {
    m_filterCenter = filterCenter;
    m_filterWidth  = filterWidth;
    drawFilter();
    update();
  }
}

void
CPlotter::setFilterEnabled(bool const filterEnabled)
{
  if (m_filterEnabled != filterEnabled)
  {
    m_filterEnabled = filterEnabled;
    drawFilter();
    update();
  }
}

void
CPlotter::setFilterOpacity(int const filterOpacity)
{
  if (m_filterOpacity != filterOpacity)
  {
    m_filterOpacity = filterOpacity;
    drawFilter();
    update();
  }
}

void
CPlotter::setFreq(int const freq)
{
  if (m_freq != freq)
  {
    m_freq = freq;
    drawMetrics();
    update();
  }
}

void
CPlotter::setPercent2DScreen(int percent2DScreen)
{
  if (m_percent2DScreen != percent2DScreen)
  {
    m_percent2DScreen = percent2DScreen;
    resize();
    update();
  }
}

void
CPlotter::setPlotGain(int const plotGain)
{
  if (m_plotGain != plotGain)
  {
    m_plotGain = plotGain;
    replot();
  }
}

void
CPlotter::setPlotZero(int const plotZero)
{
  if (m_plotZero != plotZero)
  {
    m_plotZero = plotZero;
    replot();
  }
}

void
CPlotter::setStartFreq(int const startFreq)
{
  if (m_startFreq != startFreq)
  {
    m_startFreq = startFreq;
    drawMetrics();
    drawFilter();
    update();
  }
}

void
CPlotter::setSubMode(int const nSubMode)
{
  if (m_nSubMode != nSubMode)
  {
    m_nSubMode = nSubMode;
    drawDials();
    update();
  }
}