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 <[EMAIL PROTECTED]>:
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
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