MinGW/cross-compiler
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Cross compiling a MinGW FlightGear from Cygwin or Linux
(Initial meta-note: these are instructions for how to compile FlightGear to the mingw32 (win32 APIs only, no cygwin.dll, etc...) target, *not* how to compile it using the MSYS command line environment. I presume the user already has either a working linux box or cygwin installation.)
First you need to build the MinGW cross compiler tools. (Cygwin users can skip this section and simply install the MinGW environment from the setup tool) I used the source distributions available from the GNU project instead of the MinGW trees, because the MinGW ones failed to build in linux. Either should work under Cygwin.
I am assuming that your cross compiler tools are going to live in a directory named "/mingw" Change this as appropriate.
Remember to put /mingw/bin on your path. Some of the configure scripts notice the --prefix setting and pick the right binaries up by default, but others do not, and end up defaulting to the native compiler (trust me, you don't want to spend 20 minutes compiling plib just to discover that you've built a Linux library):
export PATH=/mingw/bin:$PATH
Get the source to GNU binutils (I used version 2.15) and build it:
./configure --target=mingw32 --prefix=/mingw make make install
Now you need the MinGW C runtime and Win32 libraries and headers, because the compiler cannot build without them (this sounds like a bug to me...) Download them from the mingw.org site and unpack them into the /mingw/mingw32 directory.
cd /mingw/mingw32 tar xfz //mingw-runtime-3.2.tar.gz tar xfz //w32api-2.5.tar.gz
Now it is time to build gcc (3.3.3 in my case). This works just like the binutils step:
./configure --target=mingw32 --prefix=/mingw make make install
Pick a destination path for your FlightGear installation; I am using "/fg" here for brevity. You will need to specify this with a "--prefix=/fg" argument to all configure scripts. Don't forget.
For "native" builds many people use the /usr/local default, but for cross compilation you *must* place the resulting must in a tree by themselves.
Before compiling anything, you will need to install the dependent binary libraries (skip to the end of the section if you are happy with downloading packages I put together and don't want to read the long explanation).
You will want to install "SDK" headers and libraries for OpenAL, SDL, pthread, and zlib. The goal here is to get header files, lib*.a static libraries, and (if needed) runtime DLLs for them installed to the appropriate place: the *.a libraries go in /fg/lib, DLLs in /fg/bin, and headers under /fg/include.
Unfortunately, because the cross compilation environment is more complicated and because MSVC has traditionally been the "standard" build environment, none of these packages are as simple to install as "configure; make; make install" on a linux host, nor are they installable by default with cygwin.
The zlib library (source is packaged with SimGear) has a rather primitive non-standard configure script that simply doesn't work for building with a cross compiler or outside a Unix-like environment. I built it (just three files: libz.a, zlib.h, zconf.h) by hand. It may be possible to use the zlib implementation that ships with cygwin with a MinGW build; whether it works or not depends on whether the different underlying C libraries are sufficiently compatible.
SDL has a nicely packaged mingw32 development tarball on their website (www.libsdl.org). You can simply unpack this under /fg if you like. My version eliminates some of the unnecessary files and is somewhat smaller, but is otherwise unchanged.
The Win32 pthread library (http://sources.redhat.com/pthreads-win32) also distributes pre-compiled libraries. Unfortunately, you will have to rename them before using them. They also ship a broken header (no joke) which fails when compiled in an autoconf environment where HAVE_CONFIG_H is defined. My version fixes these problems, but is otherwise the same library.
OpenAL is the hardest to get working. First, you really want to install the binary package via the Creative installer (follow link from www.openal.org) in order to take advantage of binary-only vendor extensions from Creative and NVidia. Second, the SDK is MSVC-only, with no MinGW/Cygwin import libraries and (sigh) no meaningful directory structure. I generated libalut.a and libopenal32.a import libraries by hand from the MSVC .lib files. Unless you want to help out the OpenAL project by generating a Cygwin/MinGW build environment for them, you'll probably want to use my pre-packaged version.
Note that the openal32.dll file is *not* dumped in the /fg/bin directory; it is intended to be a system-wide library installed by the Creative installer. Also note that the alut.dll library is a separate library, not part of openal32.dll.
So to make a long story short, I put a tarball of "SDK" tarballs up at http://plausible.org/andy/fgfs-mingw-libs.tar.gz for folks to use. In side are four tar files (openal, pthread, sdl, zlib). Simply unpack each one you need in the /fg directory.
Now you are ready to compile. This part works exactly as you are used to. Note that it is important to specify --host (the target platform) and --build (the platform on which you are compiling) in order to get the configure script into "cross compilation" mode. If you specify only host, it tries to guess and sometimes gets it wrong (simple .exe files work on Linux when wine is installed!). Cygwin users should of course replace the build host with "i386-cygwin".
Plib:
./configure --host=mingw32 --build=i386-linux --prefix=/fg make make install
SimGear:
./configure --host=mingw32 --build=i386-linux --prefix=/fg make make install
FlightGear:
Note here that we can only build in the src directory. The auxilliary directories tend to be POSIX-only and are not (automatically) compilable at the moment.
./configure --host=mingw32 --build=i386-linux --prefix=/fg --enable-sdl cd src make make install
Finally, if you plan on distributing the resulting files, you will want to strip them to remove the symbol tables (the fgfs.exe file is 62 MB in my build.):
cd /fg/bin mingw32-strip *.exe