The reasons for that are twofold:
1) LINK_PRIVATE is only available since CMake 2.8.7.
2) The way it was used generated a warning because of CMake policy CMP0023:
http://www.cmake.org/cmake/help/v2.8.12/cmake.html#policy:CMP0023
Using LINK_INTERFACE_LIBRARIES actually causes another warning - this time
because of CMake policy CMP0022:
http://www.cmake.org/cmake/help/v2.8.12/cmake.html#policy:CMP0022
I set the policy to OLD, because NEW means subtle changes when compiling
with CMake 2.8.12, and I don't want to research that this close to release.
:-)
I also removed the setting of CMP0003, because it's set by
cmake_minimal_version anyway.
The patch was submitted to CMake and might be available
in the next CMake release.
But until we have the fix in CMake we should add workaround in our scripts.
The OpenGL library is not supported on Gtk3 which uses the cairo
library for rendering. Cairo, in turn uses hardware acceleration when
supported by the underlying system. Some improvement to performance
may be gained by useing the cairo-gl and cairo-glx libraries included
on modern Gtk3 systems.
See the cairo documentation for further information. The following
link may also be of interest.
http://lists.cairographics.org/archives/cairo/2012-October/023609.html
A new option WITH_GTK3 has been added to the cmake configure system to enable compilation under Gtk version 3.The flag HAVE_GTK3 is also introduced to select the new Gtk3 code in the source files. (Gtk2 is disbled when Gtk3 is selected).
window_gtk.cpp has been modified to remove obsolete (and deleted from libgtk 3) and introduce new Gtk3 code in its place when compiled for Gtk3.
To compile for Gtk2, disable WITH_GTK3 in cmake. To build for Gtk3 both WITH_GTK and WITH_GTK3 must be selected.
I didn't make the status part of the version variables here, because
letters don't play too well with version comparison algorithms
(especially with CMake's, which only supports numbers).