Client to Server Development Question

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Do any of the clients (UF, Titanium, Etc) receive information from the server that could potentially be used to modify the in-game map on the fly? Something like points with player names that would identify a players position in the zone? I am building a moba style server and it would be ideal if I could use the in-game map and emulate fog of war by only showing players in revealed areas using distance calculations. Perhaps there is a way to modify the client to do this?

I've considered hooking into the client with an external app overlay but I'd rather not require players to run an additional application on-top of the client. This is rather tacky and I just won't do it. Any ideas? I've also considered using the UF browser to display player positions (which I did try) and I was only really able to do it by generating a bitmap that placed dots on the map correlating to their x,y position but the problem is that every time the image refreshes, the browser flickers white which looks awful.