Document build of FLANN

[schuhschuh]

Building FLANN 1.8.4 with Visual Studio 2015 (and apparently also earlier versions, including the minimum required version to build MIRTK itself, i.e., VS 2013) produces a compiler error. The solution can be found in this SO thread. The following few lines have to be added to src\cpp\flann\util\serialization.h:92:

#ifdef _MSC_VER
BASIC_TYPE_SERIALIZER(unsigned __int64);
#endif

[ghisvail]

Looking at the upstream development history, the proposed fix was:

#ifdef _MSC_VER
// unsigned __int64 ~= unsigned long long
// Will throw error on VS2013
#if _MSC_VER != 1800
BASIC_TYPE_SERIALIZER(unsigned __int64);
#endif
#endif

But it was reverted here, based on feedback from a VS2015 user.

[schuhschuh]

The proper fix seems to be given in the linked issue thread then.

[ghisvail]

Dunno, seems that what the bug reporter is suggesting that the current fix (copied above) works for VS2013 and VS2015 (x86 implied here I guess), but not VS2015 x64?

[schuhschuh]

but not VS2015 x64?

That is exactly my configuration. It is worthwhile noting that I am using the latest release version of FLANN (v1.8.4, see initial issue description), not the master branch. That is the source package advertised for download on the FLANN home page and thus likely used. In any case, it'd be good to add build instructions for MIRTK dependencies for the three supported OS's (Linux, OS X, and Windows) to the online help. For FLANN, this can have a section/note for what patch is needed to build the latest release version.

It sounds like what fixed this issue indirectly was a change made for MinGW, the addition of:

BASIC_TYPE_SERIALIZER(unsigned long long);

which is apparently equivalent to

BASIC_TYPE_SERIALIZER(unsigned __int64);

for VS 2013 and 2015.

So before the addition of unsigned long long, you would think the latter is missing to get it to build with MSVC. But once unsigned long long was added, you get a duplicate definition.

[schuhschuh]

Note: FLANN_LIBRARY that is linked to on Windows must be flann_cpp_s.lib, otherwise there are unresolved LZ4 symbols which are not exported by the FLANN build. Maybe one can link to the shared flann_cpp.lib library when also adding the LZ4 library to the link dependencies, but the FLANN build includes the lz4.c source file. No linking to a LZ4 library here... Hence, it's probably best to link to FLANN statically which is anyway only used internally by mirtk::PointLocator, a wrapper around FLANN.

• Modify FindFLANN CMake BASIS module to enable looking for static C++ library (only) using the COMPONENTS argument of [basis_]find_package.

[ghisvail]

it's probably best to link to FLANN statically

👍

[schuhschuh]

New FindFLANN module added by commit 293c32f and modified dependency declarations to use static C++ library with commit bac41d1.