Method drawContours

deps/opencv/modules/imgproc/src/contours.cpp:1791–1868

}

void cv::drawContours( InputOutputArray _image, InputArrayOfArrays _contours,
                   int contourIdx, const Scalar& color, int thickness,
                   int lineType, InputArray _hierarchy,
                   int maxLevel, Point offset )
{
    Mat image = _image.getMat(), hierarchy = _hierarchy.getMat();
    CvMat _cimage = image;

    size_t ncontours = _contours.total();
    size_t i = 0, first = 0, last = ncontours;
    vector<CvSeq> seq;
    vector<CvSeqBlock> block;

    if( !last )
        return;

    seq.resize(last);
    block.resize(last);

    for( i = first; i < last; i++ )
        seq[i].first = 0;

    if( contourIdx >= 0 )
    {
        CV_Assert( 0 <= contourIdx && contourIdx < (int)last );
        first = contourIdx;
        last = contourIdx + 1;
    }

    for( i = first; i < last; i++ )
    {
        Mat ci = _contours.getMat((int)i);
        if( ci.empty() )
            continue;
        int npoints = ci.checkVector(2, CV_32S);
        CV_Assert( npoints > 0 );
        cvMakeSeqHeaderForArray( CV_SEQ_POLYGON, sizeof(CvSeq), sizeof(Point),
                                 ci.data, npoints, &seq[i], &block[i] );
    }

    if( hierarchy.empty() || maxLevel == 0 )
        for( i = first; i < last; i++ )
        {
            seq[i].h_next = i < last-1 ? &seq[i+1] : 0;
            seq[i].h_prev = i > first ? &seq[i-1] : 0;
        }
    else
    {
        size_t count = last - first;
        CV_Assert(hierarchy.total() == ncontours && hierarchy.type() == CV_32SC4 );
        const Vec4i* h = hierarchy.ptr<Vec4i>();

        if( count == ncontours )
        {
            for( i = first; i < last; i++ )
            {
                int h_next = h[i][0], h_prev = h[i][1],
                    v_next = h[i][2], v_prev = h[i][3];