ALEMBIC_DIR not used when an Alembic lib is found in default paths

[ix-dcourtois]

Description of Issue

If you have a version of Alembic library installed in the default paths (/usr/lib/ for instance on Linux, or in a folder accessible through the %PATH% env var on Windows) then the build CMake script will always use this one, not matter what you specify in -DALEMBIC_DIR=...

There are a few problems with the FindAlembic.cmake module:

• find_library is using PATHS to handle the user provided ALEMBIC_DIR, and those are used only if CMake cannot find the lib in the default paths. So if you have an Alembic lib installed in one of those default, the script will always link this one instead of the user provided one. This can be fixed by using HINTS instead of PATHS: Hints take precedence on default paths.
• LIBRARY_PATHS starts with the standard /usr/lib, etc. paths. So same as before, even if we use hints and specify a custom ALEMBIC_DIR, the one installed in /usr/lib will be used.
• The include directories are located using find_path at the end of the file, but with totally different parameters than the find_library call. And neither PATHS nor HINTS are used, thus any Alembic headers installed in default paths are found before the ones in ALEMBIC_DIR\include

I can work on a pull request, but I'd like to know if I should change the order of the paths where Alembic is looked for: I think it's best to first check in the user provided paths, and only when not found check the standard/default ones.

Steps to Reproduce

1. On Windows, update PATH to point to a folder where an Alembic lib can be found (which happens if you have a previous install of USD, see the requirements here: http://graphics.pixar.com/usd/docs/Maya-USD-Plugins.html)
2. Build USD using -DALEMBIC_DIR=<another_alemic_folder> with another Alembic lib, and check that the Alembic library used is the one in your PATH

System Information (OS, Hardware)

Windows 10 (but probably happens on all platforms)

Package Versions

0.8.3

Build Flags

[jtran56]

Filed as internal issue #156964.

[sunyab]

This fix was released with v0.8.5, closing this out. Thanks!