[rviz_rendering] replace hard coded resource location with ament_index

[wjwwood]

In ROS 1 rviz used rospkg (the ROS_PACKAGE_PATH) to find the rviz package's location to find the stuff distributed in ogre_media at runtime. As one example, see:

• https://github.com/ros-visualization/rviz/blob/3cddcb77316e326775e52bf9ca249262cba4bda7/src/rviz/ogre_helpers/render_system.cpp#L262

Right now in the rviz_rendering package we have a hard coded value to find these files, which will not work long term. See:

• rviz/rviz_rendering/src/rviz_rendering/render_system.cpp

  Line 279 in 7d93981

  std::string rviz_path = get_resource_directory();

• rviz/rviz_rendering/include/rviz_rendering/resource_config.hpp

  Line 49 in 7d93981

  set_resource_directory(const std::string & resource_directory);

• rviz/rviz_rendering/src/rviz_rendering/config.hpp.in

  Line 33 in 7d93981

  #cmakedefine RVIZ_RENDERING_PACKAGE_DIR

• rviz/rviz_rendering/CMakeLists.txt

  Lines 72 to 73 in 7d93981

  	# TODO(wjwwood): replace this with ament_index
  	PRIVATE "-DRVIZ_RENDERING_DEFAULT_RESOURCE_DIRECTORY=\"${CMAKE_CURRENT_SOURCE_DIR}\""

This should instead be replaced with finding the package's installation location using the ament_index. The idea behind the ament_index is described in detail here:

https://github.com/ament/ament_cmake/blob/master/ament_cmake_core/doc/resource_index.md

There is a cmake API, which we would use to store things in the ament index if we needed to do so:

https://github.com/ament/ament_cmake/tree/master/ament_cmake_core/cmake/index

However, if we just need the installation location of the rviz_rendering package, that part is already "registered" in the ament index with this call in the CMake:

rviz/rviz_rendering/CMakeLists.txt

Line 111 in 7d93981

ament_package()

We can access the information with the ament_index_cpp package which is C++ API for querying the ament index at runtime:

https://github.com/ament/ament_index/tree/master/ament_index_cpp

Here is an example of finding a package's location at runtime using the C++ API:

https://github.com/ros2/demos/blob/8354081d55c627b60b8e1229bdcd84d6ec036068/composition/src/api_composition.cpp#L89

There is a more direct API call in the python version ament_index_python:

https://github.com/ros2/ros2cli/blob/5584754399cb388b479814328dbf8840483ff985/ros2pkg/ros2pkg/api/__init__.py#L17

We could add that to C++ if needed.

You can introspect what is in the ament index by just browsing the files in <install prefix>/share/ament_index/resource_index.

[Martin-Idel]

Here is my understanding of this issue:

Currently, the only "resource" we require is the ogre_media folder containing the plugins.cfg file. This is as of now linked into the program during CMake and it's linked from the source folder. Obviously, that's not the way to go.

We now want two things:

a) we want the ogre_media resources to be available in the ament_index. To do this, we can register the resources and move the folders during CMake. I would think that ogre_media was its own resource to which every plugin could then contribute, i.e. we would have a file share/ament_index/resource_index/ogre_media/rviz_rendering pointing at the ogre_main folder at share/ogre_main

b) we want the location of the ogre_media package loaded at runtime (not via CMake). This can be accomplished using the ament_index_cpp package if the resources have been correctly registered. Then, whenever we call resource_config::get_resource_directory(), we just query ament_index for the location of the ogre_main resources.

Is this the way to go?

[wjwwood]

we want the ogre_media resources to be available in the ament_index.

No, I wouldn't think of the ogre_media as a resource in the ament index, though that might be something we need to do for #4.

This issue could be solved by simply getting the package's location and referencing the ogre media of this package with a relative path.

The ament index will only tell you either:

• what install prefix is a package in?
• what packages have "media for rviz"? (again this is more what [rviz_rendering] implement and document replacement for media_export #4 is about)

It does not answer:

• where are the resources relative to the install prefix?
• which resource files are being exported?

You could either hard code this information (probably the right thing to do in the case of the relative location of the resources, e.g. hard code <install prefix>/share/rviz_rendering/ogre_media) or you could include some custom data in the resource file, which might be the right thing if you need to communicate an explicit list of resources or something. However, the content of the file is not specified by the ament index, so it could be newline separated, comma separated, yaml, or whatever you want. The ament index API will only give you the text content of the file, not interpret it.

we want the location of the ogre_media package loaded at runtime (not via CMake).

Yes, but as I described above, I think the solution for this issue is to get the "package" resource which tells us at runtime (not via CMake) where the rviz_rendering package is (e.g. might be /home/me/my_cool_ws/install_with_suffix or could be /usr/local, etc...) and then we can hard code the relative path from there, i.e. share/rviz_rendering/ogre_media could be it.

[anhosi]

We are preparing a PR for this issue.