c++ - Linux draw on screen independent of windows manager -

this more of vocabulary question else.

introduction

i'm using point cloud library face tracking data. using data want track user facing on screen. not problem.

problem

to give user-feedback, draw estimation of user's face-direction red circle on screen, seen here (they create tiny window). circle able go everywhere on screen , want visible. not want covered active window. if impedes interaction window, i'm fine that.

my problem not know start.

i control cursor, less ideal, because still able move cursor while i'm using face detection.

i think need use opengl, examples i've seen have been inside x windows. example, code found here after getting hint here, give me nice permanent window, window still captures mouse clicks. how draw on screen opengl x-window independent?

am approaching wrong direction completely? if so, should googling?

i accept answer gives me starting point.

platform

i using ubuntu 12.04 unity desktop.

create regular window. tell wm skip decorations ant keep window on top. use xfixessetwindowshaperegion() separately set circular output region , empty input region. need a compositing window manager xfixes extensions work.

you can make window semi-transparent (this needs compositing window manager).

a modern toolkit such gtk should have easy use apis of above.

no opengl needed @ stage.