Simple masking for a simple 2d projection

hello there vvvv comunity. first thing im sorry if i double post…ive been searching for 2 days without hope…

i have a simple question (im really a noob)…so i mangled with v4 and obtained some nice 3d stuff synced to fft (bass) so basically i got it going. but i got stuck…i need to mask the output of a projector so it fits under an arc i have in my house…im thinking this is simple masking…is there a way? i saw the quad node…its good for other stuff…what i would want is simple 2d masking, like bezier spline or at least some other forms (circle, triangle etc) than quad. i would very much appreciate this.

ps: i also saw homography and i found a patch that has like 4 windows with some kind of polygons that you can adjust but i still cant make an arc out of it. perhaps there is a workaround…if anyone could help please