Build OpenCV with libc++ on Gentoo and static-libs

When you build C++ projects with CLang, you have the choice between using the stdlibc++ that is provided along G++ and the new libc++ that is provided by CLang.

libc++ is another implementation of the C++ Standard Library. This implementation is dual-licensed under the MIT license and UIUC license. It is especially targeting C++11 and has already 100% support for C++14. This last point is the reason that I use libc++ on several of my projects. Moreover, it is also the default on Mac OS X.

The problem with linking with another library is that you can only works with libraries that have been compiled with libc++ support. For instance, if you want to use Boost dynamic libraries, you'll have to compile Boost from sources with libc++.

For one of my project, I'm using OpenCV and libc++. To simplify the installation of OpenCV, I created a new ebuild with a libcxx use flag to selectively build the library with libc++. This requires LLVM/CLang on the build machine. Moreover, by default, the Gentoo ebuild does not have support for building the static libraries. The reason for that is that OpenCV build is not able to build dynamic and static libraries. I added a static-libs use flag that build the static libraries by building OpenCV a second time after the first. That will likely double the compile time (unless ccache is used). Anyhow, it is simple easier than to build that by hand on several machine.

The ebuild is available on my overlay. You can add the overlay to your machine by modifying /etc/layman/layman.cfg:

overlays: http://www.gentoo.org/proj/en/overlays/repositories.xml
          http://github.com/wichtounet/wichtounet-overlay/raw/master/repository.xml

Then, you can add it to layman:

layman -S
layman -a wichtounet

For now, I have created an ebuild for opencv-2.4.8-r1. If someone is interested in other versions, I'd be glad to create new ebuilds.

I hope that this ebuild will be helpful.

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