[CMake] Fwd: Targets organisation of complex project

[Chris Foster]

[ Ugh, I replied to this as a private message to Mateusz by mistake.
I'm forwarding it to the list as I hope it may be of general interest. Sorry! ]


---------- Forwarded message ----------
From: Chris Foster <chris42f at gmail.com>
Date: Mon, Oct 12, 2009 at 9:18 AM
Subject: Re: [CMake] Targets organisation of complex project
To: Mateusz Loskot <mateusz at loskot.net>


Hi Mateusz,

On Mon, Oct 12, 2009 at 5:41 AM, Mateusz Loskot <mateusz at loskot.net> wrote:
> The sources are organised in large number of subdirectories and
> sort of logical sub-libraries, but the binary output of compilation
> is a single library.
>
> Trying to figure out how to organise targets I got an idea to
> configure these sub-libraries as static library targets
> (e.g. libgdal_cpl, libgdal_alg, libgdal_gcore, etc.) which
> eventually link to single shared library (libgdal.so).

As you've seen, doing this won't work in many cases :-(

I've grappled with the same problem recently when rewriting the build system
for the aqsis renderer project.  I certainly don't know what's *best*, but I
did find a solution which somewhat satisfied me.  Let's suppose we have two
individual subdirectories, libA and libB, and we want to combine them
together.

Here's how I have laid that kind of thing out in aqsis:

src/
   CMakeLists.txt
   libA/
       project.cmake
       ... lots of source
   libB/
       project.cmake
       ... lots of source

The idea is to define a file (arbitrarily named "project.cmake" in my system)
in the individual library directories which defines variables corresponding to
the library source.  The main CMakeLists.txt then include()s these files,
makes a source list from all the individual sources, and uses those in an
add_library command to create the final library.  I wrote some macros to
automate the inclusion process a little better so that the project.cmake files
were a bit like what you'd normally write in a CMakeLists.txt.

The system has some remaining shortcomings - in particular the project.cmake
files still look more different from a plain CMakeLists.txt than I'd like -
but perhaps it can give you some ideas.  You can browse the aqsis source tree
online at

http://aqsis.git.sourceforge.net/git/gitweb.cgi?p=aqsis/aqsis;a=tree

If you're interested, I would suggest you look at the file
libs/core/CMakeLists.txt and the project.cmake files in the subdirectories of
libs/core/.  Here's an overview of the relevant directory structure:

libs/core/
   CMakeLists.txt
   api/
       project.cmake
   ddmanager/
       project.cmake
   geometry/
       project.cmake
   raytrace/
       project.cmake

To see the macros which are used (in particular, add_subproject and related
macros), have a look at the file cmake/UtilMacros.cmake

HTH,
~Chris.