Method begin

src/qt/qcustomplot.cpp:410–418

! Sets the QPainter::NonCosmeticDefaultPen in Qt versions before Qt5 after beginning painting on \a device. This is necessary to get cosmetic pen consistency across Qt versions, because since Qt5, all pens are non-cosmetic by default, and in Qt4 this render hint must be set to get that behaviour. The Constructor \ref QCPPainter(QPaintDevice *device) which directly starts painting also

  \note this function hides the non-virtual base class implementation.
*/
bool QCPPainter::begin(QPaintDevice *device)
{
  bool result = QPainter::begin(device);
#if QT_VERSION < QT_VERSION_CHECK(5, 0, 0) // before Qt5, default pens used to be cosmetic if NonCosmeticDefaultPen flag isn't set. So we set it to get consistency across Qt versions.
  if (result)
    setRenderHint(QPainter::NonCosmeticDefaultPen);
#endif
  return result;
}

/*! \overload