Provide artifacts with libtool and pkg-config files

[joschi]

Hi!

Thanks for maintaining sharp and these native libraries for libvips! They're a great help to get started. 😃

I'd like to use the native libraries provided by this project in https://github.com/criteo/JVips instead of building the libraries and maintaining their build scripts in JVips, too.

Since it's a Java project using JNI to interface with the native libraries, I need to compile a small wrapper which requires the pkg-config (*.pc) and libtool (*.la) files in order to be build.
Unfortunately, those files are removed at the end of the Linux build script:

sharp-libvips/build/lin.sh

Lines 284 to 285 in 5007da5

	cd ${TARGET}/lib
	rm -rf pkgconfig .libs *.la libvipsCC* cmake

@lovell Do you think it would be possible and sensible to provider an additional artifact with just these files for people to use the pre-built libraries of sharp-libvips and link them to their own C wrappers?

[lovell]

Is this for Linux only? Is it a problem that the .la files might contain hard-coded paths from the build machine?

These files are very small so we could put them in the main tarballs, i.e. not delete them. Happy to accept a PR if you're able.

[kleisauke]

This should be much easier now that we are building a single shared library with all its dependencies statically linked. You only have to include vips-cpp.pc, for example:

prefix=${pcfiledir}/../..
libdir=${prefix}/lib
includedir=${prefix}/include

Name: vips-cpp
Description: C++ API for vips8 image processing library
Version: 8.15.3
Requires:
Libs: -L${libdir} -l:libvips-cpp.so.42
Cflags: -I${includedir} -I${includedir}/glib-2.0 -I${libdir}/glib-2.0/include -D_GLIBCXX_USE_CXX11_ABI=0

# Download pre-built libvips binaries
mkdir -p /opt/libvips && cd /opt/libvips
curl -Ls https://github.com/lovell/sharp-libvips/releases/download/v8.15.3/libvips-8.15.3-linux-x64.tar.gz | tar -xzC .

# Download pkgconfig file
mkdir -p lib/pkgconfig && cd lib/pkgconfig
curl -OLs https://gist.github.com/kleisauke/8d93635010b371e154275e376272f8d4/raw/vips-cpp.pc

# Update the PKG_CONFIG_PATH environment variable,
# since libvips is installed in a non-standard prefix
export PKG_CONFIG_PATH=/opt/libvips/lib/pkgconfig

# Ensure dynamic linker finds the pre-built libvips binaries
export LD_LIBRARY_PATH=/opt/libvips/lib

Note that if you need to use the string overload of VImage::new_from_buffer, you must compile your project with -D_GLIBCXX_USE_CXX11_ABI=0. The pre-built binaries were compiled with the devtoolset packages on RHEL/CentOS 7 which forcefully disabled the -D_GLIBCXX_USE_CXX11_ABI=1 compiler flag, see: https://stackoverflow.com/a/52611576.

$ readelf -Ws /opt/libvips/lib/libvips-cpp.so.42 | c++filt | grep -qF "new_from_buffer(std::__cxx11::" && echo "C++11 ABI used" || echo "C++03 ABI used"
C++03 ABI used
$ readelf -Ws /usr/lib64/libvips-cpp.so.42 | c++filt | grep -qF "new_from_buffer(std::__cxx11::" && echo "C++11 ABI used" || echo "C++03 ABI used"
C++11 ABI used

[lovell]

Is this still something that might be useful? I guess the vips-cpp.pc file could be published in the @img/sharp-libvips-dev package.

[kleisauke]

It could still be useful, I think.

FWIW, I just updated https://gist.github.com/kleisauke/8d93635010b371e154275e376272f8d4 to make vips-cpp.pc relocatable, similar to what is done when you build with Meson's pkgconfig.relocatable option.