Add support for headless mode

[saikishor]

Fixes: #20
@pgesel-rai FYI

In future, we can add some changes, like if we set the headless parameter from the launch file, we can toggle the behaviour

[pgesel-rai]

When I echo /joint_states, I am seeing all zeros. It appears the simulation is not running. However, this may be due testing this change on the humble-devel branch. @saikishor Maybe you have more context, it looks like there are difference, specially with mj_data_control_.

[saikishor]

When I echo /joint_states, I am seeing all zeros. It appears the simulation is not running. However, this may be due testing this change on the humble-devel branch. @saikishor Maybe you have more context, it looks like there are difference, specially with mj_data_control_.

When I checked with rolling it did, I can check it again this evening

[saikishor]

@pgesel-rai I just tested the setup with ros2 launch mujoco_ros2_simulation test_robot.launch.py headless:=true and it works when I send a command both with headless to true and false

[pgesel-rai]

I am going to do some more testing. I wonder if the effort based controller I am running can cause issues. Are you using a position interface?

[saikishor]

I am going to do some more testing. I wonder if the effort based controller I am running can cause issues. Are you using a position interface?

Yes!!

mujoco_ros2_simulation/test/test_resources/test_robot.xml

Lines 44 to 47 in 040657b

	<actuator>
	<position name="joint1" joint="joint1" kp="1000" dampratio="1.0"/>
	<position name="joint2" joint="joint2" kp="1000" dampratio="1.0"/>
	</actuator>

[pgesel-rai]

I messed up the backport. This works on the Humble branch. Looks good!

[saikishor]

I messed up the backport. This works on the Humble branch. Looks good!

I'm glad it is working. Can you approve the PR, if the changes look good to you?

[eholum-nasa]

Fantastic! Works beautifully for me on jazzy. Just minor nits about adding some comments.

@pgesel-rai If you have a functional back port ready to go can you open a PR for the humble branch? This is something that we would use on humble, too.

[eholum-nasa]

🚀