@Carl Love A PlotComponent allows for properties (clickx clicky) to be queried programatically. Those can be used with a single right-click, or click&drag.
The `Explore` command allows for this by having two (or one) parameters be specified via its `markers` option. Additionally, the corresponding Sliders may be shown, or suppressed. See ?Explore as well as ?examples,Explore .
The above have a notion that the scale of the parameters is the same as the scale of the 2D plot. Naturally, if the interactive plot is 3D then such marker-style interaction (on a 2D plot area) would need to be in a separate plot, by the side say.
I'm away from a computer until this coming Sunday and then again from Mon-Fri. Apologies not being to show examples by code.
[edit. If I can paste properly...]
The parameter values taken from a 2D plotting area can be used as simply the x,y values of an input point. Or they can be used as a pair of parameters used in some quite different manner of your own devising.
IIRC, here's an Explore app that used markers to grab an x-y point input on-the-fly,
And here's an embedded components app that also used clickx,clicky (but not via Explore) to control parameters,