Render plugin force for debugging

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I have a plugin that is applying a force on a link, and I would want that plugin to inject a visual for that force into the link. For instance, say that the link is a box, and my plugin applies a force on the side of the box that makes it translate in the world, I would want my plugin to add an arrow showing that force.

Because I don't know how to make an arrow, for now let's say I just draw a sphere where that force applies. So in my plugin's Load function, I get the model and the SDF:

void MyPlugin::Load(physics::ModelPtr model, sdf::ElementPtr sdf)

I can get the link, say my_link, with model->GetLink("my_link"). And I would like to inject the following visual into it:

  <visual name='test_sphere_visual'>
    <pose>0 0 1</pose>
    <geometry>
      <sphere>
          <radius>0.05</radius>
      </sphere>
    </geometry>
  </visual>

I have been following the "spawn spheres" tutorial, where I successfully manage to create an msgs::Model from a string and inject it into the world. But in this case, instead of injecting a whole new model, I want to inject a visual into an existing link.

Is there a way to do that from a plugin?