Method updatePaintNode

app/src/UI/Widgets/PlotAreaFill.cpp:453–503

* @brief Rebuilds the fill from the per-column envelopes: one O(points) accumulation * pass, then O(item width) vertex emission, so geometry cost is independent of * data density. The per-vertex alpha ramps from kMaxAlpha at the largest * per-sign deviation down to kMinAlpha at the baseline, anchoring the gradient * to the data instead of the axis range. */

 *        to the data instead of the axis range.
 */
QSGNode* Widgets::PlotAreaFill::updatePaintNode(QSGNode* oldNode, UpdatePaintNodeData* data)
{
  Q_UNUSED(data)

  const double w      = width();
  const double h      = height();
  const double xRange = m_xMax - m_xMin;
  const double yRange = m_yMax - m_yMin;

  const QList<QPointF> points = m_source ? m_source->points() : QList<QPointF>();

  const bool valid =
    points.size() >= 2 && std::isfinite(m_baseline) && xRange > 0 && yRange > 0 && w > 0 && h > 0;
  if (!valid) {
    delete oldNode;
    return nullptr;
  }

  const int cols = std::min(kMaxColumns, static_cast<int>(std::ceil(w)));
  accumulateColumns(points, cols, w);

  double refPositive = 0;
  double refNegative = 0;
  const int filled   = scanColumns(refPositive, refNegative);
  if (filled == 0) {
    delete oldNode;
    return nullptr;
  }

  auto* node = static_cast<QSGGeometryNode*>(oldNode);
  if (!node) {
    node           = new QSGGeometryNode;
    auto* geometry = new QSGGeometry(QSGGeometry::defaultAttributes_ColoredPoint2D(), 0);
    geometry->setDrawingMode(QSGGeometry::DrawTriangleStrip);
    node->setGeometry(geometry);
    node->setFlag(QSGNode::OwnsGeometry);
    node->setMaterial(new QSGVertexColorMaterial);
    node->setFlag(QSGNode::OwnsMaterial);
  }

  const int vertexCount = 8 * filled - 2;
  auto* geometry        = node->geometry();
  Q_ASSERT(geometry != nullptr);
  if (geometry->vertexCount() != vertexCount)
    geometry->allocate(vertexCount);

  emitColumns(geometry->vertexDataAsColoredPoint2D(), vertexCount, w, h, refPositive, refNegative);

  node->markDirty(QSGNode::DirtyGeometry);
  return node;
}