macos confusion about libpbg version

[edwardhartnett]

When I added a test for PNG and it ran on the mac, I get this:

12/12 Test #12: tst_png ..........................***Failed    0.10 sec
33
libpng warning: Application built with libpng-1.4.12 but running with 1.6.37
34
Testing PNG functions.
35
Testing enc_png() call...-1

Turns out this is a known macos issue: https://stackoverflow.com/questions/36523911/osx-homebrew-cmake-libpng-version-mismatch-issue

[edwardhartnett]

OK, this was fixed for macos by changing the CMakeLists.txt file to:

link_directories("/usr/local/lib")
if(USE_PNG)
  find_package(ZLIB REQUIRED)
  find_package(PkgConfig REQUIRED)
  pkg_check_modules(PNG libpng16 REQUIRED)
#  find_package(PNG REQUIRED)
else()
  message(STATUS "Will not build PNG support")
endif()

This was as described here: https://stackoverflow.com/questions/36523911/osx-homebrew-cmake-libpng-version-mismatch-issue

@kgerheiser @aerorahul did I do the right thing here?

Also, I presume that the g2 project would have the same problem with macOS and PNG, and we will discover it as we add tests to that project...

[DusanJovic-NOAA]

Please do not make changes like this anymore. If PNG installation is broken on Mac it should be fixed there. Or if Mac specific code needs to be added to this project then it must be in added Mac specific if section.

[edwardhartnett]

What do we mean by "changes like this?" ;-)

I will be making many changes to this library. We (the NCEPLIBS team and Arun) recently had a meeting in which we mapped out our development plans with respect to GRIB code. We have some nice ambitious plans! ;-) No longer will these libraries languish, neglected and untested. A new day is dawning for this code!

However, backward compatibly will be preserved.

[dusanjovic]

By 'changes like this' I mean changes that are platform specific. "/usr/local/lib" does not necessarily exist on all platforms. Platform specific code should be in if(....) .... endif() sections.