Function cvDrawContours

deps/opencv/modules/core/src/drawing.cpp:2372–2490

    ((count) -= ((count) == (seq)->total && !CV_IS_SEQ_CLOSED(seq)))

CV_IMPL void
cvDrawContours( void* _img, CvSeq* contour,
                CvScalar _externalColor, CvScalar _holeColor,
                int  maxLevel, int thickness,
                int line_type, CvPoint _offset )
{
    CvSeq *contour0 = contour, *h_next = 0;
    CvTreeNodeIterator iterator;
    cv::vector<cv::PolyEdge> edges;
    cv::vector<cv::Point2l> pts;
    cv::Scalar externalColor = _externalColor, holeColor = _holeColor;
    cv::Mat img = cv::cvarrToMat(_img);
    cv::Point offset = _offset;
    double ext_buf[4], hole_buf[4];

    if( line_type == CV_AA && img.depth() != CV_8U )
        line_type = 8;

    if( !contour )
        return;

    CV_Assert( thickness <= 255 );

    scalarToRawData( externalColor, ext_buf, img.type(), 0 );
    scalarToRawData( holeColor, hole_buf, img.type(), 0 );

    maxLevel = MAX(maxLevel, INT_MIN+2);
    maxLevel = MIN(maxLevel, INT_MAX-1);

    if( maxLevel < 0 )
    {
        h_next = contour->h_next;
        contour->h_next = 0;
        maxLevel = -maxLevel+1;
    }

    cvInitTreeNodeIterator( &iterator, contour, maxLevel );
    while( (contour = (CvSeq*)cvNextTreeNode( &iterator )) != 0 )
    {
        CvSeqReader reader;
        int i, count = contour->total;
        int elem_type = CV_MAT_TYPE(contour->flags);
        void* clr = (contour->flags & CV_SEQ_FLAG_HOLE) == 0 ? ext_buf : hole_buf;

        cvStartReadSeq( contour, &reader, 0 );
        if( thickness < 0 )
            pts.resize(0);

        if( CV_IS_SEQ_CHAIN_CONTOUR( contour ))
        {
            cv::Point pt = ((CvChain*)contour)->origin;
            cv::Point prev_pt = pt;
            char prev_code = reader.ptr ? reader.ptr[0] : '\0';

            prev_pt += offset;

            for( i = 0; i < count; i++ )
            {