How to know if Graphic object is being displayed?

[c-s]

In that case, you should also look at the display-context option. As the documentation notes, when a Visual's display-context is non-null, it's attached to a graphical hierarchy or otherwise able to be displayed; if it's null, then you know it's definitely not being displayed. Able to be displayed doesn't necessary mean being displayed, so you would also want to check the View.visibility as mentioned above if the option is non-null if you're interested in seeing if it's really on-screen.

So, roughly:

1. Is display-context null? If so, stop: we're not displayed.
2. Else is get-view null? If so, again, stop: we're either being printed or not in an actual View.
3. Else is View.visibility hidden or minimized? If so, stop: the View is out of the user's visibility.
   

Note that it's OK to check these values -- except note that if you're calling get-view that requires layout validation so be careful about when your timing -- but be cautious about moving Visuals around or setting key options in response to changes, or you may end up with invalidation loops or similar trouble.