[vtk-developers] Re: Fwd: Re: Compiling VTK-5.0.2 with Cygwin make

Steve Robbins smr at sumost.ca
Thu Sep 21 15:37:33 EDT 2006

Quoting Steve Robbins <smr at sumost.ca>:

To recap: I am building VTK 5 sources on cygwin under windows XP.  The  
initial build failed with link errors.  Cygwin provides two different  
OpenGL implementations: one that runs on top of X11 and one that  
doesn't.  The cause of the link errors is that the compilation used  
gl.h from X11 but linked against the non-X11 GL library.

I configured with VTK_USE_X set to OFF.

> Note that VTK_USE_X is off: so why am I picking up
> -I/usr/X11R6/include?  Hmmm....

The answer is that CMakeCache.txt had the following line:

So why is that?  It appears to me that there's a bug somewhere in  
CMake (I'm using  CMake version 2.4-patch 3).  There's no agreement on  
whether having CYGWIN true should imply that WIN32 is true.  The  
symbol CYGWIN is set by the CMakeCCompiler, CMakeCXXCompiler, and  
CMakeFortranCompiler.  All of these set UNIX but don't set WIN32.  The  
module FindOpenGL, however, only tests CYGWIN when WIN32 is also true.

In particular, here is the code from FindOpenGL that searches for the  
OpenGL include path:

IF (WIN32)



For non-X11 builds, the correct location for GL/gl.h is  
/usr/include/w32api.  But since WIN32 is not defined, we go through  
the second FIND_PATH() and end up with -I/usr/X11R6/include on the  

I'm not really sure what to suggest as a fix: should CMakeCCompiler  
and friends define WIN32 or should FindOpenGL be overhauled?


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