UMat.fromRange constructor
creates a matrix header for a part of the bigger matrix
UMat(const UMat& m, const Range& rowRange, const Range& colRange=Range::all());
https://docs.opencv.org/4.x/d7/d45/classcv_1_1UMat.html#afeaabd3e9eef98ccef422a81176a4250
Implementation
factory UMat.fromRange(UMat umat, {int rowStart = 0, int? rowEnd, int colStart = 0, int? colEnd}) {
final p = calloc<cvg.UMat>();
rowEnd ??= umat.rows;
colEnd ??= umat.cols;
cvRun(() => ccore.cv_UMat_create_7(umat.ref, rowStart, rowEnd!, colStart, colEnd!, p));
return UMat._(p);
}