RViz plug-in which is neither a Tool, Display, nor a Panel

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Hi all,

I'm looking for a way to take a screenshot of the current view in RViz from the code and output it in png. RViz is already able to take screenshots through the GUI, so I assume it would not be so much effort to code a little bit more and write a plugin that:

1. Subscribes to a ROS topic waiting for a screenshot order
2. Takes a screenshot of the current view when such an order is received
3. Publishes it somewhere as a sensor_msgs::Image for instance or in a temporarily png

But this kind of plug-in is neither a tool, a panel or a Display, just some code running in background as soon as the plug-in is loaded. What's the better way to do that easily?

Please note that my screenshot orders would be sent automatically and periodically by another node, I don't want any GUI annoying the user when screenshots occur, and it must not be a tool as soon as the user may be using other tools during this time (Interact, Camera, ...).

Any help or advice is welcome, Many thanks