filter2D function
Implementation
VARP filter2D(VARP src, int ddepth, VARP kernel, {double delta = 0, int borderType = BORDER_REFLECT}) {
final pOut = c.mnn_cv_filter2D(src.ptr, ddepth, kernel.ptr, delta, borderType);
final rval = VARP.fromPointer(pOut);
return rval;
}