As the title says, I’m trying to enable the zapper in retroarch 1.2.2. I’m using the Nestopia core. I see no options whatsoever in core input remapping or otherwise. Help please? 
Hmm. Typically, you would load the content up and then go into settings > input settings and change the Player 2 input device type from NES Pad or whatever to Zapper, but that doesn’t seem to be an option with either Nestopia or FCEUmm. I’ll try talking to rdanbrook about it, as it’s probably just not hooked up at the moment.
I just spoke to him and it turns out that you need the NstDatabase.xml in your ‘system’ directory so Nestopia knows it’s a Zapper game, at which point you should get a crosshair and it should start accepting mouse input.
Awesome! Thank you. I now have regular NES games working. However, how do I go about adding games like VS Duck Hunt and VS Hogan’s Alley? I looked at the xml and I’m not sure how to get the data it wants to plug those in.
those are part of the MAME set…so the setup would be different.