the trick is just mounting $wsys and optionally supply some window attributes in the mount spec. see rio(1) and /sys/src/libdraw/newwindow.c
after that, you have the new window mounted on /dev and a following initdraw() will pick it up. if you want to maintain multiple windows for your program, its better to mount each window somewhere else and supply windir. its unusual for plan9 programs to make ther own windows tho. instead, its more common to create windows/layers inside your screen (like sam or acme). -- cinap
