So a lime window you can get from

Lib.application.windows

has a private variable called

__backend

which will give you a

NativeWindow

on native targets like desktop. The

NativeWindow

has a public variable called

handle

which is the sdl window but it is

Dynamic

. You will probably need to write some externs to set that opacity. I haven't done anything like that before, but that is where it is as far as I can tell.