For my office remodel, I had a large window and two french doors to paint. I decided to try liquid masking for the glass since cutting-in 34 panes x 2 coats is not my idea of fun.
I tried some kind of liquid mask many years ago and wasn't impressed, but there are newer products and they get good reviews. You paint (or spray) the masking onto the glass. You don't have to cut it in, any that gets on the wood just gets painted over, and if you have bare wood or bare spots, the mask acts as a primer. You can mask all the glass if you will be spray painting; in my case I'm painting by hand so I just masked a 2" or so band around each edge of each pane. After the mask dries (4 hours to overnight) you paint, with no need to cut-in; you just brush or spray the paint over the masking. After all the coats of paint are applied and dry, you scribe around each pane lightly with a utility knife and then peel off the masking, leaving a nice clean edge behind.
I've only done the 4 large panes so far, but the stuff works great! It peels off easily and cleanly and the paint edge is straighter and cleaner than I could get on my best day just cutting in. I'll probably try spraying the mask on when I do the doors since there are 15 panes in each door.