Use relative install paths for plugin shared libraries and media files

[azeey]

🦟 Bug fix

Summary

Fixes an error when building https://github.com/gazebo-release/gz_rendering_vendor/ in the ROS buildfarm.

Similar to gazebosim/gz-tools#137

Checklist

• Signed all commits for DCO
• Added tests
• Updated documentation (as needed)
• Updated migration guide (as needed)
• Consider updating Python bindings (if the library has them)
• codecheck passed (See contributing)
• All tests passed (See test coverage)
• While waiting for a review on your PR, please help review another open pull request to support the maintainers

Note to maintainers: Remember to use Squash-Merge and edit the commit message to match the pull request summary while retaining Signed-off-by messages.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 75.68%. Comparing base (e187f52) to head (f2ecc4f).

❗ Current head f2ecc4f differs from pull request most recent head f13205e. Consider uploading reports for the commit f13205e to get more accurate results

Additional details and impacted files

@@              Coverage Diff               @@
##           gz-rendering8     #984   +/-   ##
==============================================
  Coverage          75.68%   75.68%           
==============================================
  Files                177      177           
  Lines              16959    16959           
==============================================
  Hits               12835    12835           
  Misses              4124     4124           

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

[azeey]

Based on gazebosim/gz-physics#616 (comment), I've reverted changes to GZ_RENDERING_ENGINE_INSTALL_DIR and GZ_RENDERING_RESOURCE_PATH and instead used GZ_RENDERING_ENGINE_RELATIVE_INSTALL_DIR and GZ_RENDERING_RELATIVE_RESOURCE_PATH in f13205e

One way I've found to test this is to go into the build directory and run

cmake -DCMAKE_ERROR_ON_ABSOLUTE_INSTALL_DESTINATION=ON -P cmake_install.cmake

(Make sure to have the latest version of gz-cmake3)

[caguero]

Just checking, are the Windows CI issues expected?

[azeey]

Just checking, are the Windows CI issues expected?

I believe so. Here's the build for the gz-rendering8 branch: https://build.osrfoundation.org/job/gz_rendering-8-win/38/testReport/