knnMatch method
KnnMatch Finds the k best matches for each descriptor from a query set.
For further details, please see: https://docs.opencv.org/master/db/d39/classcv_1_1DescriptorMatcher.html#aa880f9353cdf185ccf3013e08210483a
Implementation
VecVecDMatch knnMatch(Mat query, Mat train, int k) {
final ret = calloc<cvg.VecVecDMatch>();
cvRun(() => cffi.BFMatcher_KnnMatch(ptr.ref, query.ref, train.ref, k, ret));
return VecVecDMatch.fromPointer(ret);
}