Try linking from gphoto2 from package config

[tenderlove]

If gphoto2 was found in package config, but was not found via the normal find_path / find_library calls, try looking again but with the paths supplied by pkg-config

This is probably a niche usecase, but tethering wasn't working with my OM-1 Mkii. I tracked the problem to a bug in libgphoto2, and sent a PR to fix libgphoto2. I was able to confirm that gphoto2 could control my camera, but I wanted to test darktable integration. I installed a development version of libgphoto2 to a special directory, and even though I could get CMake to find my pkg-config files, it wouldn't compile / link against them. I added the code in this PR to try compiling and linking against gphoto2 found in pkg-config so I could verify my changes fixed darktable too.

Here's a screenshot of darktable tethering with my OM-1 Mkii:

I know this is a niche usecase, so it's fine if my PR is rejected. But I wanted to send it in case someone else is trying to test edge versions of dependencies (or maybe there's an easier way I don't know).

Thanks!

[TurboGit]

Looks good to me but I'll prefer a CMake expert look at this, @kmilos can you review ?

[kmilos]

This looks very contorted and unnecessary to me...

What is the exact problem you're trying to solve, can you provide some output when trying to link to libghpoto2 in a custom location?

[tenderlove]

What is the exact problem you're trying to solve, can you provide some output when trying to link to libghpoto2 in a custom location?

I've installed libgphoto2 to $HOME/.local/lib. I set PKG_CONFIG_PATH to $HOME/.local/lib/pkgconfig. I expected the CMake configuration to compile and link against the values returned by pkg-config, but instead it searches the system libraries for libgphoto2 and uses pkg-config to determine the version.

If I specify PKG_CONFIG_PATH, pkg-config will pick up the right cflags etc:

$ PKG_CONFIG_PATH="$HOME/.local/lib/pkgconfig" pkg-config --cflags libgphoto2
-I/Users/aaron/.local/include -I/Users/aaron/.local/include/gphoto2 -I/opt/homebrew/Cellar/libexif/0.6.25/include

AFAICT the find_library call will not consult pkg-config for paths to search.

Here is the script I'm using to build:

begin
  set -lx DEVELOPER_DIR "/Applications/Xcode.app/Contents/Developer"
  set -lx CC cc
  set -lx CXX c++
  set -lx MACOSX_DEPLOYMENT_TARGET 14.0
  set -lx SRC_DIR $HOME/git/darktable
  set -lx BUILD_DIR $SRC_DIR/build
  set -lx INSTALL_PREFIX $BUILD_DIR/macosx
  set -lx ECO "-DBINARY_PACKAGE_BUILD=ON -DBUILD_CURVE_TOOLS=ON -DBUILD_NOISE_TOOLS=ON -DUSE_GRAPHICSMAGICK=OFF -DUSE_IMAGEMAGICK=ON"
  set -lx CMAKE_BUILD_TYPE Release
  set -lx GENERATOR Ninja
  set -lx TARGET skiptest
  set -lx PKG_CONFIG_PATH $HOME/.local/lib/pkgconfig

  pushd $SRC_DIR
  git submodule init
  git config submodule.src/tests/integration.update none
  git submodule update
  popd

  pushd $SRC_DIR

  cmake -E make_directory $BUILD_DIR
  cmake -E make_directory $INSTALL_PREFIX
  $SRC_DIR/.ci/ci-script.sh
  $SRC_DIR/packaging/macosx/3_make_hb_darktable_package.sh

  popd
end

Here is the logfile made by building on master.

Here is the logfile made from building on my branch.

On master:

-- Could NOT find Gphoto2 (missing: Gphoto2_LIBRARY Gphoto2_INCLUDE_DIR) (Required is at least version "2.5")

On my branch:

-- Found Gphoto2: /Users/aaron/.local/lib/libgphoto2.dylib (Required is at least version "2.5")

otool output on master (it's empty):

$ otool -l build/macosx/bin/darktable | grep gphoto

otool output on my branch:

$ otool -l build/macosx/bin/darktable | grep gphoto
         name /Users/aaron/.local/lib/libgphoto2.6.dylib (offset 24)
         name /Users/aaron/.local/lib/libgphoto2_port.12.dylib (offset 24)

I think this PR could be rewritten like this:

diff --git a/cmake/modules/FindGphoto2.cmake b/cmake/modules/FindGphoto2.cmake
index 936122c75d..e1d3726cdf 100644
--- a/cmake/modules/FindGphoto2.cmake
+++ b/cmake/modules/FindGphoto2.cmake
@@ -19,19 +19,21 @@
 
 include(LibFindMacros)
 
-find_path(Gphoto2_INCLUDE_DIR gphoto2/gphoto2.h)
-mark_as_advanced(Gphoto2_INCLUDE_DIR)
 
 set(Gphoto2_NAMES ${Gphoto2_NAMES} gphoto2 libgphoto2)
 set(Gphoto2_PORT_NAMES ${Gphoto2_PORT_NAMES} gphoto2_port libgphoto2_port)
-find_library(Gphoto2_LIBRARY NAMES ${Gphoto2_NAMES} )
-find_library(Gphoto2_PORT_LIBRARY NAMES ${Gphoto2_PORT_NAMES} )
-mark_as_advanced(Gphoto2_LIBRARY)
-mark_as_advanced(Gphoto2_PORT_LIBRARY)
 
 # Detect libgphoto2 version
 libfind_pkg_check_modules(Gphoto2_PKGCONF libgphoto2)
 if(Gphoto2_PKGCONF_FOUND)
+  find_path(Gphoto2_INCLUDE_DIR gphoto2/gphoto2.h PATHS ${Gphoto2_PKGCONF_INCLUDE_DIRS} )
+  mark_as_advanced(Gphoto2_INCLUDE_DIR)
+
+  find_library(Gphoto2_LIBRARY NAMES ${Gphoto2_NAMES} PATHS ${Gphoto2_PKGCONF_LIBRARY_DIRS} )
+  find_library(Gphoto2_PORT_LIBRARY NAMES ${Gphoto2_PORT_NAMES} PATHS ${Gphoto2_PKGCONF_LIBRARY_DIRS} )
+  mark_as_advanced(Gphoto2_LIBRARY)
+  mark_as_advanced(Gphoto2_PORT_LIBRARY)
+
   set(Gphoto2_VERSION_STRING "${Gphoto2_PKGCONF_VERSION}")
 endif()

But I'm not a CMake expert. Also I suspect I could manually pass CFLAGS etc, but since the build scripts require gphoto2 to be available via pkg-config, it seems like we should use the paths pkg-config tell us to use.

Hope this makes sense. Thank you for your patience.

[kmilos]

Yep, the FindGphoto2.cmake module is not really implemented in the best way, find_path is called before any pkgconf stuff, which is indeed a bit strange? I might try to refactor the whole thing at some point...

Btw, are we sure gphoto2 ships a .pc file on all platforms? (It does for me on MSYS2 at least.)

[kmilos]

@tenderlove Can you please give #18875 a go instead?