OK, I think I've got the kinks worked out of the MinGW work, and
have written up a little README (attached) describing how the
process works.  Thanks to Norman and Frederic for the pointer to
the pthread library.

The required changes are in CVS now, and the process has been
tested at least on my Fedora box.  Hopefully this will be helpful
to the windows users who have been left a little behind by the
recent SDL and OpenAL changes, or maybe to someone who wants to
set up an automated build system for windows binaries.

Andy
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 /<wherever>/mingw-runtime-3.2.tar.gz
  tar xfz /<wherever>/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

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