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From:	"Matt D." <codespunk AT gmail DOT com>
To:	cygwin AT cygwin DOT com
Reply-To:	codespunk+cygwin AT gmail DOT com
Subject:	What is the purpose of libglut32?
Message-ID:	<dcc6471d-f995-52b8-2770-1f523ae34ae6@gmail.com>
Date:	Thu, 27 Sep 2018 08:48:01 -0400
User-Agent:	Mozilla/5.0 (Windows NT 10.0; WOW64; rv:52.0) Gecko/20100101 Thunderbird/52.8.0
MIME-Version:	1.0

Does anyone know what libglut32 is used for? It comes as part of 
"w32api-runtime" and "mingw64-i686-runtime" and is installed into:

usr/lib/w32api/libglut32.a

and

usr/i686-w64-mingw32/sys-root/mingw/lib/libglut32.a

I haven't been able to find a use for this as attempting to link with it 
produces the following errors:

undefined reference to `_imp____glutInitWithExit AT 12'
undefined reference to `_imp____glutCreateWindowWithExit AT 8'
undefined reference to `_imp____glutCreateMenuWithExit AT 8'

It is possible to link with it if -DGLUT_DISABLE_ATEXIT_HACK is used to 
skip these declarations but then it depends upon glut32.dll which isn't 
provided by any package. How can libglut32 be used for anything if it is 
missing its binary dependency? Is this library unused? Is the glut32.dll 
dependency an error?

Also note that this define really isn't meant to be used since it 
disables a necessary workaround as defined in freeglut_std.h.

See here:

 > Win32 has an annoying issue where there are multiple C run-time
 > libraries (CRTs). If the executable is linked with a different CRT
 > from the GLUT DLL, the GLUT DLL will not share the same CRT static
 > data seen by the executable. In particular, atexit callbacks
 > registered in the executable will not be called if GLUT calls its
 > (different) exit routine. GLUT is typically built with the
 > "/MD" option (the CRT with multithreading DLL support), but the Visual
 > C++ linker default is "/ML" (the single threaded CRT).
 >
 > One workaround to this issue is requiring users to always link with
 > the same CRT as GLUT is compiled with. That requires users supply a
 > non-standard option. GLUT 3.7 has its own built-in workaround where
 > the executable's "exit" function pointer is covertly passed to GLUT.
 > GLUT then calls the executable's exit function pointer to ensure that
 > any "atexit" calls registered by the application are called if GLUT
 > needs to exit.
 >
 > Note that the __glut*WithExit routines should NEVER be called
 > directly. To avoid the atexit workaround, #define
 > GLUT_DISABLE_ATEXIT_HACK.

This library is NOT the same as libgut, which seems to be the 
appropriate way to include glut, even when compiling for MinGW.


Matt D.

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