[vtkusers] Multiple installation

[LL]

Dear VTK-users

Here is a useful hack for those experimenting with multiple versions of
VTK (as in different ABIs or cross-platform libraries). It relies on the
fact that in $(VTK_SRC)/system.make, VTK_LIB_EXT is different from
SHLIB_SUFFIX. Thus if you define (say)

VTK_VERSION = 3.2
VTK_LIB_EXT          = ${VTK_VERSION}.so

then modify the other linked libraries in the various makes to use this
(e.g. -lVTKGraphics${VTK_VERSION}  ) you can trick the make process to
generate different versions.

For example, Kit.make

libVTK$(ME)Python$(VTK_LIB_EXT): libVTK$(ME)$(VTK_LIB_EXT) \
        python/${ME}Init.o ${PYTHON_O_ADD} ${PYTHON_WRAP}
        rm -f libVTK$(ME)Python$(VTK_LIB_EXT)
        $(CXX) ${CXX_FLAGS} ${VTK_SHLIB_BUILD_FLAGS} \
        -o libVTK$(ME)Python$(VTK_LIB_EXT) python/${ME}Init.o \
        ${PYTHON_O_ADD} ${PYTHON_WRAP}  -L. ${XLDFLAGS} \
        ${PYTHON_LIBS}  ${XLIBS} -lXext -lXt ${X_PRE_LIBS} -lX11 \
        ${X_EXTRA_LIBS} ${DL_LIBS} ${THREAD_LIBS}

then in places like install_python, you can add
        @echo "Switching to version {VTK_VERSION}"
        (cd $(LIB_INSTALL_DIR); \
         rm -rf libVTK${ME}Python${SHLIB_SUFFIX};
         ln -s libVTK${ME}Python${VTK_LIB_EXT}
libVTK${ME}Python${SHLIB_SUFFIX})


Caveats -
1) this does not modify the *.make.in so some of the changes (e.g. to
system.make) will be lost when you do a ./configure
2) I have not tested with with non-shared libraries and other variations
of config options, it may affect some other static options
3) there are some spots which need a bit of hand-massaging as they
redefine the linked libraries rather than taking their cues from
system.make. It should work as normal when you set VTK_VERSION to NULL

Where this is useful, if you are using different python installations
(which complains about C API mismatch) or trying some experimental
modifications without destroying a working test-case.

LL