Using CMakePackageConfigHelpers, we can generate a relocatable
OpenJPEGConfig.config, using the PATH_VARS feature to make
CMAKE_INSTALL_LIBDIR relative to the installed location.
This change is needed for me when cross-compiling since
CMAKE_INSTALL_FULL_LIBDIR is a path inside the sysroot rather than
an absolute path to the actual includes. Without this change poppler
ends up passing a -I flag that does not exist.
This includes fallback code for CMake 2.8, which adds a bit of complexity,
since I'm not sure if raising the minimum to 3.0 (now over 8 years old)
is acceptable.
* Add GNUInstallDirs for standard installation directories
Distributions are given standard variables for already existing hooks.
Multiarch libdirs is taken care of automagically.
Raises minimum cmake version by a little.
* Handle CMAKE_INSTALL_xxx being absolute paths for .pc file generation
In some cases the CMAKE_INSTAL_{BIN,MAN,DOC,LIB,INCLUDE}DIR variables
may turn out to be absolute paths in which case prepending ${prefix} in
the pkg-config .pc files will result in incorrect values.
For .pc file generation, figure out if these variables are absolute and
omit the prefix in the configured file when so.
See: ab25e4b7ed
Alex Richardson
Thomas Bracht Laumann Jespersen
Fabrice Fontaine
Matthew Sharp
Libor Bukata
Mathieu Malaterre