Your tutorial project is very helpful, thanks. I use CMake, too (along with QT Creator). I'm not very adept in it, yet, so your CMake scripts are also interesting for me.
I'm not entirely sure what you mean with "avoiding modifications to the external libraries", though. Were you referring to how I split up SFML in separate directories for headers and platform- and compiler-specific bins and libs? I was inspired by way SFML handled external libraries, as the SFML repository contains DLLs and libs for OpenAL and libsndfile. They're added like this in /src/SFML/CMakeLists.txt:
I thought I could do it in a similar fashion.
Or should I rather use the script FindSFML.cmake instead? I just recently payed attention to this script.
In regards to SFML, it makes sense for that library to supply the includes/libs/dll's in a cleaned up manner as the point of SFML is easy use and distribution. This is different than writing a game though where the focus is not on easy distribution so much as it is on getting the job done. Let's say it takes a couple hours to build all the variations of SFML, make copies of the includes, put the binaries where you want them etc, that's a couple hours you could be coding on the game instead of fiddling with trivialities. With the solution I use in the tutorials project, if I upgrade SFML I just drop it into the extern folder and point the listfile to the new location, delete the old version and keep working on my game. 5 minutes (ok, 10 if you count the extra build time for the new version ) versus a couple hours.
As to making no modifications, I mean that it should be literally a matter of downloading the new source package, unzip to the extern directory and update the CMake list files to point at the new version. Anything beyond that, or perhaps very trivial modifications, is just too much of a hassle generally. The libraries which come with SFML are not exactly my favorite thing, but then again, building FreeType2 is a pain in the ass (on Windows at least) and SFML is coded against those versions so I have no problem using them, this is an exception to my normal rules though.
As to using FindSFML, as Hodgman says, I want a self contained project, so I build SFML as part of my solution. Different library versions, compiler flags etc are too painful later, I want to basically have a directory I can zip and drop on another machine and it just "works" without the user having to do a bunch of nonsense. At most, and only on Windows, I generally have to point folks at the VC redistributable to get that installed, other than that I want no other worries in distribution. This is an experience thing, back in the bad days I released a game and we were debugging oddball startup failures, game crashes etc for almost a month because of different libraries installed on different machines and all the hassles that involves. I wouldn't wish such an experience on anyone, especially the users..