Building OpenGL from source

["Zieg, Mark" <mark dot zieg at lmco dot com>]

Hello,

Pardon if this is an easy one, but I've been looking at it for a few
days and haven't found an "easy" solution.  If anyone can issue me a few
adroit pointers (or kicks), I'd be most grateful.

PROBLEM
-------

I need to be able to build and run an OpenGL implementation from source
on Windows.  Performance isn't an issue, so it doesn't need to have any
hardware acceleration, but I need to be able to tweak specific equations
and constants within the source code.

OBSERVATIONS
------------

It looks like the default Cygwin OpenGL libraries are basically just
pass-throughs to the pre-compiled Microsoft implementation; is that
correct?  Since MS probably isn't about to open up the source to their
version, I went looking for open-source implementations.  SGI's
ogl-sample and the Mesa3D version both looked promising; perhaps
Chromium if neither of those pan out.

However, I'm finding it's "easier said than done" to get one of those
compiling and linked into Cygwin's X11R6 installation.  For instance,
Mesa3D doesn't seem to come with a "cygwin" configuration.  I hacked one
from the provided "linux-static" version and was able to compile, but
the teapot demo coredumps on its first(?) call to glGetString:

  LOG INFO   :  teapot: Teapot V1.2
  LOG INFO   :  teapot: Written by David Bucciarelli (tech.hmw@plus.it)
  LOG INFO   :  teapot: calling glutInit...
  LOG INFO   :  teapot: calling inittextures...
  LOG TRACE  :    inittextures: [entering]
  LOG INFO   :      inittextures: glGenTextures...
  LOG INFO   :      inittextures: glBindTexture...
  LOG INFO   :      inittextures: glPixelStorei...
  LOG INFO   :      inittextures: LoadRGBMipmaps...
  LOG TRACE  :        LoadRGBMipmaps: [entering]
  LOG TRACE  :            LoadRGBMipmaps2: [entering]
  LOG INFO   :              LoadRGBMipmaps2: calling tkRGBImageLoad:
../images/tile.rgb
  LOG TRACE  :                tkRGBImageLoad: [entering]
  LOG TRACE  :                tkRGBImageLoad: [returning]
  LOG INFO   :              LoadRGBMipmaps2: checking that image was
returned
  LOG INFO   :              LoadRGBMipmaps2: determining format from
number of components
  LOG INFO   :              LoadRGBMipmaps2: looks like RGB
  LOG INFO   :              LoadRGBMipmaps2: calling gluBuild2DMipmaps
  LOG INFO   :                gluBuild2DMipmaps: calling closestFit...
  LOG INFO   :                  closestFit: start
  LOG INFO   :                  closestFit: calling
glGetString(GL_VERSION)
  Segmentation fault (core dumped)

I wasn't sure where that was coming from, so I temporarily set that path
aside and tried looking at the SGI ogl-sample build instructions.  It
seemed to state that, like it or not, I was probably going to have to
build X11 from scratch if I wanted to change OpenGL implementations.  

So then I took a full CVS checkout of Xorg (per
http://x.cygwin.com/docs/cg/prog-obtaining-source.html) and built it.
That went surprisingly smooth (great job, maintainers!), but all my
teapot examples still seemed to want to link against
/usr/lib/w32api/*32.a, which I gather are not touched by the Xorg
installation.  I tried pointing my teapot app to /usr/X11R6/lib, which
has these intriguingly named libraries:

  libGL-1.dll.a
  libGL.dll.a
  libGLU-1.dll.a
  libGLU.dll.a
  libGLw.a

However, trying to link against those spat out lots of undefined
references:

  make[1]: Entering directory `/home/ziegm/opengl/teapot'
  g++ teapot.o -L/usr/X11R6/lib -lglut -lGLU -lGL -o teapot
  teapot.o:teapot.cpp:(.text+0xd2): undefined reference to
`_glClearColor@16'
  teapot.o:teapot.cpp:(.text+0xe1): undefined reference to
`_glShadeModel@4'
  teapot.o:teapot.cpp:(.text+0x11d): undefined reference to
`_glMaterialfv@12'
  teapot.o:teapot.cpp:(.text+0x159): undefined reference to
`_glLightfv@12'
  teapot.o:teapot.cpp:(.text+0x1fe): undefined reference to
`_glEnable@4'
  teapot.o:teapot.cpp:(.text+0x27c): undefined reference to
`_gluLookAt@72'
  ...etc

My assumption (!) from those results is that the full Xorg build is
still "noticing" that I'm on Cygwin/Windows, and is therefore
"helpfully" linking its own code against the w32api/MS libraries.  (I
really don't understand enough about this process to confirm or refute
that theory, however.)

However, I do see that the Mesa code shipped with Xorg under "extras" is
indeed being compiled and linked into an "libOSMesa.dll.a" archive.
However, linking against that didn't resolve any of the above linker
errors.  To try to confirm whether these files were even being used, I
added a bunch of "printf's" to extras/Mesa/src/mesa/*/*light.c
(apparently symlinked to lib/GL/mesa and programs/Xserver/GL/mesa), yet
running teapot (linked against /usr/lib/w32api) generated nary a
message.

Am I even on the right track?  Is there an easier way to do this?  If
you needed to intercept and customize a few specific OpenGL functions
(say, the lighting model), under Windows, preferably via Cygwin, how
would you go about it?

Thank you for any help you may provide,

Mark Zieg