[vtkusers] Re: Compiling VTK-5.0.2 with Cygwin make

[Patrick D. Emond]

For those people who, like me, are primarily interested in getting VTK5 
built under cygwin the simplest solution seems to be to make sure that 
your cygwin install has no X11 libraries installed.  I completely 
reinstalled cygwin making sure to not include any X11 packages and the 
VTK install went off without a hitch (no need to change the 
CMakeCache.txt file after running CMake).

Hope that helps someone.

- Patrick


Steve Robbins wrote:
> Hello all,
> 
> This thread begins at 
> http://public.kitware.com/pipermail/vtkusers/2006-September/087106.html
> 
> 
> Quoting Steve Robbins <smr at sumost.ca>:
> 
>> I'm having the same problem as Patrick D. Emond
>> [http://public.kitware.com/pipermail/vtkusers/2006-September/086953.html] 
>> in
>> building VTK under cygwin.
> 
> 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.  However, CMake saw fit to add 
> -I/usr/X11R6/include to the compile command line and therefore brought 
> in the
> wrong gl.h.
> 
> In a series of emails with helpful folks like David Cole and Brad King I 
> learned the following:
> 
> 0. A workaround exists: after configuring, edit CMakeCache.txt to set
> the OPENGL_* variables correctly, reconfigure, and build.
> 
> 1. The only way to debug CMake's actions is to sprinkle MESSAGE() 
> throughout
> its input files, including those in /usr/share/cmake-2.4.3.
> 
> 2. The symbol WIN32 *is* defined on cygwin, contrary to my initial 
> speculation.
> 
> 3. The file /usr/share/cmake-2.4.3/Modules/FindOpenGL.cmake has the 
> following
> code:
> 
> IF (WIN32)
>   IF (CYGWIN)
> 
>     FIND_PATH(OPENGL_INCLUDE_DIR GL/gl.h
>       /usr/include
>       /usr/include/w32api
>       /usr/X11R6/include
>     )
> 
> Despite the existence of /usr/include/w32api/GL/gl.h, the variable 
> OPENGL_INCLUDE_DIR is set to /usr/X11R6/include by this code.  This is
> *not* an effect of CMake caching, nor have I defined the environment
> variable INCLUDE.
> 
> What is happening is that FIND_PATH() searches an internal, hard-coded set
> of paths *before* the paths specified in the arguments.  This set of
> paths happens to include /usr/X11R6/include, so if that directory contains
> GL/gl.h, there's no way /usr/include/w32api/GL/gl.h (the correct, non-X11
> header) will be found.
> 
> At this point, deep in a private email thread, the speculation became
> that the internal set of include paths was in the wrong order.  In fact,
> however, there is no possible correct ordering if one wants to support
> building with both versions of OpenGL, based on a build-time configuration
> variable (VTK_USE_X).  Rather, I think, the code in FindOpenGL.cmake should
> resemble the following:
> 
> IF(VTK_USE_X)
>   FIND_PATH( OPENGL_INCLUDE_DIR GL/gl.h /usr/X11R6/include 
> NO_DEFAULT_PATH )
> ELSE
>   FIND_PATH( OPENGL_INCLUDE_DIR GL/gl.h /usr/include/w32api 
> NO_DEFAULT_PATH )
> ENDIF
> 
> The trouble is, of course, that FindOpenGL.cmake has no knowledge of
> "VTK_USE_X".
> 
> It's clear that there's a bug: building on cygwin should work 
> out-of-the-box
> for both settings of VTK_USE_X.  It's less clear (to me) whether the bug 
> should
> be fixed in VTK or in CMake.
> 
> -Steve
> 
>