I've added OpenBSD support to libpano13. As you can see in the
patch(openbsd_support.patch), it was pretty easy.
The compilation doesn't work out of the box though as there is a
problem in libpng detection (as a matter of fact, on OpenBSD, libpng
has its include files in /usr/local/include/libpng ans the libs are
in /usr/local/lib, a situation not taken into account in the m4 macros
available with libpano).
To solve that problem, I made another patch (libpng_detection.patch)
that uses pkg-config rather than a home-made macro. This solves my
problem and should still hopefully work on Linux.
Both patch can be applied against latest head.
Hope that helps.