Instead use win_has_alpha to check for alpha channel, window mode is
reserved for determine if the window is possibly transparent.
Signed-off-by: Yuxuan Shui <yshuiv7@gmail.com>
Also move static function prototypes out of compton.h. Seems like the
previous developers didn't know what header files are for.
Seems to have bugs after the split.
Yuxuan Shui