I would like to know if Emacs treats empty portions of the frame as faces. I want to know because I wonder if the background of an Emacs frame is drawn separately of other elements on the screen.
EDIT: I have done some experiments and found that on X11, Emacs uses the function "x_clear_area" to fill in the background color of empty potions of the frame. Background for spaces and non-visible characters is handled by the draw method of the "font_driver" struct (xfont_draw/xftfont_draw).
EDIT2: Now I am very confused, there seem to be multiple places where the background is being drawn. Does anybody know where are all the places this happens on X11 build ?