Method getTraverse

projects/gui/3rdparty/qcustomplot/qcustomplot.cpp:23696–23782

! \internal This function is part of the curve optimization algorithm of \ref getCurveLines. This method assumes that the \ref mayTraverse test has returned true, so there is a chance the segment defined by (\a prevKey, \a prevValue) and (\a key, \a value) goes through the visible region 5. The return value of this method indicates whether the segment actually traverses region 5

  exit points of region 5. They will become the optimized points for that segment.
*/
bool QCPCurve::getTraverse(double prevKey, double prevValue, double key, double value, double keyMin, double valueMax, double keyMax, double valueMin, QPointF &crossA, QPointF &crossB) const
{
  // The intersection point interpolation here is done in pixel coordinates, so we don't need to
  // differentiate between different axis scale types. Note that the nomenclature
  // top/left/bottom/right/min/max is with respect to the rect in plot coordinates, wich may be
  // different in pixel coordinates (horz/vert key axes, reversed ranges)
  
  QList<QPointF> intersections;
  const double valueMinPx = mValueAxis->coordToPixel(valueMin);
  const double valueMaxPx = mValueAxis->coordToPixel(valueMax);
  const double keyMinPx = mKeyAxis->coordToPixel(keyMin);
  const double keyMaxPx = mKeyAxis->coordToPixel(keyMax);
  const double keyPx = mKeyAxis->coordToPixel(key);
  const double valuePx = mValueAxis->coordToPixel(value);
  const double prevKeyPx = mKeyAxis->coordToPixel(prevKey);
  const double prevValuePx = mValueAxis->coordToPixel(prevValue);
  if (qFuzzyIsNull(keyPx-prevKeyPx)) // line is parallel to value axis
  {
    // due to region filter in mayTraverse(), if line is parallel to value or key axis, region 5 is traversed here
    intersections.append(mKeyAxis->orientation() == Qt::Horizontal ? QPointF(keyPx, valueMinPx) : QPointF(valueMinPx, keyPx)); // direction will be taken care of at end of method
    intersections.append(mKeyAxis->orientation() == Qt::Horizontal ? QPointF(keyPx, valueMaxPx) : QPointF(valueMaxPx, keyPx));
  } else if (qFuzzyIsNull(valuePx-prevValuePx)) // line is parallel to key axis
  {
    // due to region filter in mayTraverse(), if line is parallel to value or key axis, region 5 is traversed here
    intersections.append(mKeyAxis->orientation() == Qt::Horizontal ? QPointF(keyMinPx, valuePx) : QPointF(valuePx, keyMinPx)); // direction will be taken care of at end of method
    intersections.append(mKeyAxis->orientation() == Qt::Horizontal ? QPointF(keyMaxPx, valuePx) : QPointF(valuePx, keyMaxPx));
  } else // line is skewed
  {
    double gamma;
    double keyPerValuePx = (keyPx-prevKeyPx)/(valuePx-prevValuePx);
    // check top of rect:
    gamma = prevKeyPx + (valueMaxPx-prevValuePx)*keyPerValuePx;
    if (gamma >= qMin(keyMinPx, keyMaxPx) && gamma <= qMax(keyMinPx, keyMaxPx)) // qMin/qMax necessary since axes may be reversed
      intersections.append(mKeyAxis->orientation() == Qt::Horizontal ? QPointF(gamma, valueMaxPx) : QPointF(valueMaxPx, gamma));
    // check bottom of rect:
    gamma = prevKeyPx + (valueMinPx-prevValuePx)*keyPerValuePx;
    if (gamma >= qMin(keyMinPx, keyMaxPx) && gamma <= qMax(keyMinPx, keyMaxPx)) // qMin/qMax necessary since axes may be reversed
      intersections.append(mKeyAxis->orientation() == Qt::Horizontal ? QPointF(gamma, valueMinPx) : QPointF(valueMinPx, gamma));
    const double valuePerKeyPx = 1.0/keyPerValuePx;
    // check left of rect:
    gamma = prevValuePx + (keyMinPx-prevKeyPx)*valuePerKeyPx;
    if (gamma >= qMin(valueMinPx, valueMaxPx) && gamma <= qMax(valueMinPx, valueMaxPx)) // qMin/qMax necessary since axes may be reversed
      intersections.append(mKeyAxis->orientation() == Qt::Horizontal ? QPointF(keyMinPx, gamma) : QPointF(gamma, keyMinPx));
    // check right of rect:
    gamma = prevValuePx + (keyMaxPx-prevKeyPx)*valuePerKeyPx;
    if (gamma >= qMin(valueMinPx, valueMaxPx) && gamma <= qMax(valueMinPx, valueMaxPx)) // qMin/qMax necessary since axes may be reversed
      intersections.append(mKeyAxis->orientation() == Qt::Horizontal ? QPointF(keyMaxPx, gamma) : QPointF(gamma, keyMaxPx));
  }
  
  // handle cases where found points isn't exactly 2:
  if (intersections.size() > 2)
  {
    // line probably goes through corner of rect, and we got duplicate points there. single out the point pair with greatest distance in between:
    double distSqrMax = 0;
    QPointF pv1, pv2;
    for (int i=0; i<intersections.size()-1; ++i)
    {
      for (int k=i+1; k<intersections.size(); ++k)