Enable/disable: gravity and static

[ahcorde]

🎉 New feature

Summary

Allow to enable/disable gravity and static state

Test it

Checklist

• Signed all commits for DCO
• Added tests
• Added example and/or tutorial
• 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)
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[ahcorde]

@scpeters and/or @azeey do you have some time to review this one ?

[azeey]

gazebosim/gz-sim#3189 added the ability to change gravity at runtime. Is it still necessary to add aa feature to enable/disable gravity? What's the expected behavior when gravity is disabled, but then it's changed to be a non-zero value with the API in gazebosim/gz-sim#3189?

[ahcorde]

gazebosim/gz-sim#3189 added the ability to change gravity at runtime. Is it still necessary to add aa feature to enable/disable gravity? What's the expected behavior when gravity is disabled, but then it's changed to be a non-zero value with the API in gazebosim/gz-sim#3189?

If there is no need to calculate gravety, It's more clear to disable it than set to zero. Probrably internally in the physics engines are less calculations.

[ahcorde]

@scpeters or @caguero opinions here ?

[scpeters]

gazebosim/gz-sim#3189 added the ability to change gravity at runtime. Is it still necessary to add aa feature to enable/disable gravity? What's the expected behavior when gravity is disabled, but then it's changed to be a non-zero value with the API in gazebosim/gz-sim#3189?

If there is no need to calculate gravety, It's more clear to disable it than set to zero. Probrably internally in the physics engines are less calculations.

gazebosim/gz-sim#3189 uses the World Get/Set Gravity feature from #275, while this is adding the equivalent of Model::SetGravityMode from gazebo-classic. Is there a particular use case motivating this, or is it mainly to improve feature parity with gazebo-classic?

[ahcorde]

@azeey @scpeters and @caguero ready for another pass

[ahcorde]

friendly ping @azeey @scpeters and @caguero

[caguero]

Is this functionality working with nested models? This might be a good pattern if not. Consider to add tests using nested models as well.

[ahcorde]

Is this functionality working with nested models? This might be a good pattern if not. Consider to add tests using nested models as well.

I will take a look to the nested models. I was testing some ideas and it's not working. I can do this in a follow up PR