I think that opening a window and rendering something inside it using the native Win32 API from assembly code on Windows would not be so terrifyingly complex. It's just more code as it needs to call the appropriate GUI APIs (not just syscalls), and it's OS-specific... but such code is anyway always OS-specific (the one mentioned here seems to be for Linux, given the used syscalls). No idea how complex it would be with X or on Mac, as I don't know their low-level GUI APIs.