QGIS Core Centroid NEW

/* /src/core/qgscentralpointpositionmanager.cpp */
int QgsCentralPointPositionManager::calculatePolygonCentroid( double x[], double y[], int numberOfPoints, double& centroidX, double& centroidY ) const
{
  register int i, j;
  double ai, atmp = 0, xtmp = 0, ytmp = 0;
  if ( numberOfPoints < 3 )
  {
    return 1;
  }

  for ( i = numberOfPoints - 1, j = 0; j < numberOfPoints; i = j, j++ )
  {
    ai = ( x[i] - x[0] ) * ( y[j] - y[0] ) - ( x[j] - x[0] ) * ( y[i] - y[0] );
    atmp += ai;
    xtmp += ( x[j] + x[i] - 2 * x[0] ) * ai;
    ytmp += ( y[j] + y[i] - 2 * y[0] ) * ai;
  }
  if ( atmp == 0 )
  {
    return 2;
  }
  centroidX = x[0] + xtmp / ( 3 * atmp );
  centroidY = y[0] + ytmp / ( 3 * atmp );
  return 0;
}