Method drawXAxis

app/src/UI/Widgets/Waterfall.cpp:940–983

* @brief Draws the frequency axis (X) -- grid, tick marks, labels. */

 * @brief Draws the frequency axis (X) -- grid, tick marks, labels.
 */
void Widgets::Waterfall::drawXAxis(QPainter* painter, const QRectF& plotRect) const
{
  if (m_samplingRate <= 0)
    return;

  const double nyquist = m_samplingRate * 0.5;
  const double srcW    = nyquist / m_xZoom;
  const double maxPan  = qMax(0.0, (nyquist - srcW) * 0.5);
  const double center  = nyquist * 0.5 + qBound(-maxPan, m_xPan * nyquist, maxPan);
  const double xMinHz  = center - srcW * 0.5;
  const double xMaxHz  = center + srcW * 0.5;

  const AxisTicks ticks = computeFreqTicks(srcW, kAxisTickCount);

  const QFontMetrics fm(painter->font());
  const double tickTopY = plotRect.bottom();
  const double tickBotY = plotRect.bottom() + kAxisTickPx;
  const double labelY   = tickBotY + kAxisLabelPad;

  const double step      = ticks.step;
  const double invStep   = 1.0 / step;
  const double first     = std::ceil(xMinHz * invStep - 1e-9) * step;
  const double xRange    = xMaxHz - xMinHz;
  const double invXRange = xRange > 0.0 ? 1.0 / xRange : 0.0;

  for (double v = first; v <= xMaxHz + 1e-6; v += step) {
    const double t = (v - xMinHz) * invXRange;
    if (t < 0.0 || t > 1.0)
      continue;

    const double x = plotRect.left() + t * plotRect.width();

    painter->setPen(QPen(m_gridColor, 1, Qt::DotLine));
    painter->drawLine(QPointF(x, plotRect.top()), QPointF(x, plotRect.bottom()));

    painter->setPen(QPen(m_borderColor, 1));
    painter->drawLine(QPointF(x, tickTopY), QPointF(x, tickBotY));

    const QString label  = formatFreqTick(v);
    const int labelWidth = fm.horizontalAdvance(label);
    painter->setPen(m_textColor);
    painter->drawText(QPointF(x - labelWidth * 0.5, labelY + fm.ascent()), label);
  }
}

/**
 * @brief Draws the Y axis (time or Campbell-mode dataset value).