Fix linker error to gst_base_sink_get_type

[RFRIEDM-Trimble]

This should actually fix the #12 by properly linking gstreamer libs.

• Use PkgConfig populated variables correctly
• Stop linking to strings that aren't targets
• Add alias library for gscam_node

Note: ament_target_dependencies is on its way out in favor of modern cmake calls to target_link_libraries.
ament/ament_cmake#292

It's out of scope of this bug fix, but upgrading to modern cmake in this library would be favorable to make it easier and more robust to consume.

References:

• https://stackoverflow.com/questions/64078308/how-to-write-a-cmake-file-which-successfully-links-gstreamer-basic-tutorial-5
• https://zhangboyi.gitlab.io/post/2020-09-14-resolve-dso-missing-from-command-line-error/#:~:text=The%20DSO%20missing%20from%20command,a%20directly%20specified%20dynamic%20library
• See copy-dt-needed-entries on https://linux.die.net/man/1/ld
• https://cmake.org/cmake/help/latest/module/FindPkgConfig.html

[RFRIEDM-Trimble]

CI failed on rolling due to this failure:

 -- Found ament_cmake: 1.2.1 (/opt/ros/rolling/share/ament_cmake/cmake)
  -- Found Python3: /usr/bin/python3.8 (found version "3.8.10") found components: Interpreter 
  -- Override CMake install command with custom implementation using symlinks instead of copying resources
  CMake Error at CMakeLists.txt:35 (find_package):
    By not providing "Findcamera_calibration_parsers.cmake" in
    CMAKE_MODULE_PATH this project has asked CMake to find a package
    configuration file provided by "camera_calibration_parsers", but CMake did
    not find one.
  
    Could not find a package configuration file provided by
    "camera_calibration_parsers" with any of the following names:
  
      camera_calibration_parsersConfig.cmake
      camera_calibration_parsers-config.cmake

In the galactic build, it is found here:

-- Found camera_calibration_parsers: 2.3.1 (/opt/ros/galactic/share/camera_calibration_parsers/cmake)

Will try to get a rolling environment set up to see if I can reproduce this issue.

[clydemcqueen]

Hi, thanks for this contribution! LGTM+++

I'm learning a bunch of CMake by reading the changes the you made and diving around to understand the syntax. I am very open to any/all changes you'd like to propose.

CI failed on rolling due to this failure:

I think this is a bug in the CI, I am still building Rolling in Focal, not Jammy. See:

gscam2/.github/workflows/build_test.yml

Line 29 in 687a975

- docker_image: rostooling/setup-ros-docker:ubuntu-focal-ros-rolling-ros-base-latest

I will merge this PR as-is and then fix CI in a separate PR.

[RFRIEDM-Trimble]

Hi, thanks for this contribution! LGTM+++

I'm learning a bunch of CMake by reading the changes the you made and diving around to understand the syntax. I am very open to any/all changes you'd like to propose.

CI failed on rolling due to this failure:

I think this is a bug in the CI, I am still building Rolling in Focal, not Jammy. See:

gscam2/.github/workflows/build_test.yml

Line 29 in 687a975

- docker_image: rostooling/setup-ros-docker:ubuntu-focal-ros-rolling-ros-base-latest

I will merge this PR as-is and then fix CI in a separate PR.

Excellent! Thanks for merging. Hopefully the links I supplied are useful for your learning.

I tried replacing the libraries in ament_target_dependencies to another call of target_link_libraries as one should, however the upstream libraries don't support alias targets and Config mode exports (yet). I've filed the issue upstream here, so if I can get traction on that and implement it, then the modern cmake support can also be improved here.