Add support for pip install

[matthewdcong]

This PR adds preliminary support for pip install. Assuming that the dependencies required for building OpenVDB and NanoVDB are installed, then pip install <openvdb_source_root> will

1. Build OpenVDB, NanoVDB, and their corresponding Python bindings.
2. Install these Python bindings and dependent libraries in the site-packages directory
3. Enable the user to import openvdb and import nanovdb when launching Python.

This is a first-step towards making installation of OpenVDB easier for new users, and will help users dive into the library via the Python interface.

[linux-foundation-easycla]

The committers listed above are authorized under a signed CLA.

• ✅ login: matthewdcong / name: Matthew Cong (5e4bb9f, 40d1089, 18ad210)

[matthewdcong]

Why is the CLA check failing?

[danrbailey]

Why is the CLA check failing?

Just pushed a commit and it's failing for me as well, let me message John...

[jmertic]

/easycla

[danrbailey]

Wondering if there's a cleaner way to handle this kind of case without all of this conditional branching. What about using an INSTALL_PREFIX and including the forward slash in the prefix (although potentially needs thought for multi-platforms):

if (SKBUILD)
  set(INSTALL_PREFIX "openvdb/")
else
  set(INSTALL_PREFIX "")
endif()

install(TARGETS openvdb_static
  RUNTIME_DESTINATION ${INSTALL_PREFIX}${CMAKE_INSTALL_BINDIR}
)

Ultimately, it would be nice to use less if (SKBUILD) logic if possible?

[matthewdcong]

Yeah, I'm not a huge fan of all the SKBUILD logic either. I'm happy to take another look.

In an ideal world, it'd be possible to separate them entirely, but in practice Python packaging has very limited support for two modules in a single package. Thus, we need to delegate a lot of the pip install location logic to CMake since Python just doesn't provide us with the expressiveness to do so hence the SKBUILD custom logic.

[matthewdcong]

Thanks for the suggestions @danrbailey ! I've consolidated the conditional branching significantly. Please take another look and let me know what you think.

[danrbailey]

This is much better, thanks Matt! Just one small comment which I think is probably a find-replace typo...

[danrbailey]

There are a few of these variables that are swapping INCLUDE paths for ROOT paths?

[matthewdcong]

Not a typo I think.

Prior to this change, NANOVDB_INSTALL_INCLUDE_DIR (note the underscore between include and dir) was already defined. I've renamed NANOVDB_INSTALL_INCLUDE_DIR to NANOVDB_INSTALL_ROOT_DIR in order to avoid confusion with the newly introduced/very similarly named NANOVDB_INSTALL_INCLUDEDIR (that defaults to CMAKE_INSTALL_INCLUDEDIR).

[danrbailey]

Ah, that makes sense, thanks for explaining.

[apradhana]

Tested on Linux with the latest changes. LGTM.