Method start

deps/opencv/modules/imgproc/src/filter.cpp:204–303

static const int VEC_ALIGN = CV_MALLOC_ALIGN;

int FilterEngine::start(Size _wholeSize, Rect _roi, int _maxBufRows)
{
    int i, j;

    wholeSize = _wholeSize;
    roi = _roi;
    CV_Assert( roi.x >= 0 && roi.y >= 0 && roi.width >= 0 && roi.height >= 0 &&
        roi.x + roi.width <= wholeSize.width &&
        roi.y + roi.height <= wholeSize.height );

    int esz = (int)getElemSize(srcType);
    int bufElemSize = (int)getElemSize(bufType);
    const uchar* constVal = !constBorderValue.empty() ? &constBorderValue[0] : 0;

    if( _maxBufRows < 0 )
        _maxBufRows = ksize.height + 3;
    _maxBufRows = std::max(_maxBufRows, std::max(anchor.y, ksize.height-anchor.y-1)*2+1);

    if( maxWidth < roi.width || _maxBufRows != (int)rows.size() )
    {
        rows.resize(_maxBufRows);
        maxWidth = std::max(maxWidth, roi.width);
        int cn = CV_MAT_CN(srcType);
        srcRow.resize(esz*(maxWidth + ksize.width - 1));
        if( columnBorderType == BORDER_CONSTANT )
        {
            constBorderRow.resize(getElemSize(bufType)*(maxWidth + ksize.width - 1 + VEC_ALIGN));
            uchar *dst = alignPtr(&constBorderRow[0], VEC_ALIGN), *tdst;
            int n = (int)constBorderValue.size(), N;
            N = (maxWidth + ksize.width - 1)*esz;
            tdst = isSeparable() ? &srcRow[0] : dst;

            for( i = 0; i < N; i += n )
            {
                n = std::min( n, N - i );
                for(j = 0; j < n; j++)
                    tdst[i+j] = constVal[j];
            }

            if( isSeparable() )
                (*rowFilter)(&srcRow[0], dst, maxWidth, cn);
        }

        int maxBufStep = bufElemSize*(int)alignSize(maxWidth +
            (!isSeparable() ? ksize.width - 1 : 0),VEC_ALIGN);
        ringBuf.resize(maxBufStep*rows.size()+VEC_ALIGN);
    }

    // adjust bufstep so that the used part of the ring buffer stays compact in memory
    bufStep = bufElemSize*(int)alignSize(roi.width + (!isSeparable() ? ksize.width - 1 : 0),16);

    dx1 = std::max(anchor.x - roi.x, 0);
    dx2 = std::max(ksize.width - anchor.x - 1 + roi.x + roi.width - wholeSize.width, 0);

    // recompute border tables
    if( dx1 > 0 || dx2 > 0 )
    {
        if( rowBorderType == BORDER_CONSTANT )