Load plugins

[mmurooka]

This change allows the use of plugins such as https://github.com/isri-aist/MujocoTactileSensorPlugin I just copied part of https://github.com/deepmind/mujoco/blob/main/simulate/main.cc, but it may be modified to fit this project if necessary.

[mmurooka]

Just as Choreonoid automatically loads plugin libraries in the directory of the environment variable CNOID_PLUGIN_PATH, I think it may be a good idea to introduce MUJOCO_PLUGIN_PATH.

[rohanpsingh]

Hi @mmurooka san! I'm unable to play the video file in the README. What does the tactile sensor do? Is it different from the touch sensor introduced recently?

[mmurooka]

Hi @rohanpsingh I've updated the video so you can play it now. My plugin (MujocoTactileSensorPlugin) is implemented based on the touch grid plugin in the MuJoCo repo, with the following differences.

• The touch grid plugin handles the contact forces in a site frame common to all sensor patches, whereas MujocoTactileSensorPlugin handles them in the frame of each sensor patch to accurately simulate tactile sensor measuring normal forces.
• Supports both square and hexagonal grids for sensor arrays (I'm thinking of simulating a hexagonal grid sensor.)
• Sensor values can be published as a ROS topic.

Anyway, this PR is intended to allow general plugins, including those in the MuJoCo repo, to be used with mc_mujoco.

[mmurooka]

Just as Choreonoid automatically loads plugin libraries in the directory of the environment variable CNOID_PLUGIN_PATH, I think it may be a good idea to introduce MUJOCO_PLUGIN_PATH.

I've updated it in this way.

The following is a use case of this PR. By loading the MujocoRosUtils::PosePublisher plugin in mc_mujoco with this PR, when running LocomanipController in mc_mujoco, the pose of the cart model is obtained via ROS topics.

https://github.com/rohanpsingh/mc_mujoco/assets/6636600/7567c53a-d372-479d-b540-ce6e03a7c7e8

[gergondet]

Hi @mmurooka

This looks good to me. However, may I ask that you consider the following:

1. Consider using a configuration entry in mc_mujoco.yaml to define the search path (that would complement the MUJOCO_PLUGIN_PATH environment variable)
2. Maybe rename MUJOCO_PLUGIN_PATH to MC_MUJOCO_PLUGIN_PATH such that there's no confusion about it
3. Add some information in the README about the functionality

Thanks

[mmurooka]

Hi @gergondet Thanks for your comment. I think I have addressed all of them. I have eliminated support for the environment variable because I began to feel that it fits better with the concept of mc_rtc. Feel free to modify the entry name, doc, etc.

[mmurooka]

I have rebased the commits to eliminate the changelog in main.cpp.