Method emitColumns

app/src/UI/Widgets/PlotAreaFill.cpp:394–444

* @brief Emits one six-vertex column per filled column (peak quad above the baseline, * valley quad below, sharing the baseline edge where the alpha pinches to * kMinAlpha), stitched into a single strip with two degenerate vertices. */

 *        kMinAlpha), stitched into a single strip with two degenerate vertices.
 */
void Widgets::PlotAreaFill::emitColumns(QSGGeometry::ColoredPoint2D* vertices,
                                        const int vertexCount,
                                        const double w,
                                        const double h,
                                        const double refPositive,
                                        const double refNegative) const
{
  Q_ASSERT(vertices != nullptr);
  Q_ASSERT(refPositive > 0.0);
  Q_ASSERT(refNegative > 0.0);

  const double sy    = h / (m_yMax - m_yMin);
  const float base_y = static_cast<float>((m_yMax - m_baseline) * sy);

  auto ramp = [](const double dev, const double ref) -> double {
    return kMinAlpha + (kMaxAlpha - kMinAlpha) * std::min(1.0, dev / ref);
  };

  int j                  = 0;
  const std::size_t cols = m_colMin.size();
  for (std::size_t c = 0; c < cols; ++c) {
    const double lo = m_colMin[c];
    const double hi = m_colMax[c];
    if (hi < lo)
      continue;

    const double a_top = hi > m_baseline ? ramp(hi - m_baseline, refPositive) : kMinAlpha;
    const double a_bot = lo < m_baseline ? ramp(m_baseline - lo, refNegative) : kMinAlpha;

    const float x0    = static_cast<float>(c);
    const float x1    = static_cast<float>(std::min(static_cast<double>(c + 1), w));
    const float y_top = static_cast<float>((m_yMax - std::max(hi, m_baseline)) * sy);
    const float y_bot = static_cast<float>((m_yMax - std::min(lo, m_baseline)) * sy);

    if (j > 0) {
      vertices[j] = vertices[j - 1];
      ++j;
      setVertexColor(vertices[j++], x0, y_top, m_fillColor, a_top);
    }

    setVertexColor(vertices[j++], x0, y_top, m_fillColor, a_top);
    setVertexColor(vertices[j++], x1, y_top, m_fillColor, a_top);
    setVertexColor(vertices[j++], x0, base_y, m_fillColor, kMinAlpha);
    setVertexColor(vertices[j++], x1, base_y, m_fillColor, kMinAlpha);
    setVertexColor(vertices[j++], x0, y_bot, m_fillColor, a_bot);
    setVertexColor(vertices[j++], x1, y_bot, m_fillColor, a_bot);
  }

  Q_ASSERT(j == vertexCount);
  Q_UNUSED(vertexCount)
}

/**
 * @brief Rebuilds the fill from the per-column envelopes: one O(points) accumulation