You'd need to use Inline with => 'PDL' to make available PDL's C functions. Then, to know what PDL C functions to actually call, consult PDL::API.

The imminent PDL::OpenCV (not on CPAN yet, but see https://github.com/PDLPorters/pdl/issues/362) shows how to call from PDL C code into C++ via a wrapper, if that's any use.

EDIT: "how to" is too strong - "one way to" would be better.