For big windows, their shadow images might exceed the maximum request length limit of Xorg. libxcb will shutdown the connection to X server if we try to send that image. So we have to break the image apart and send it piecemeal. In the future we probably should migrate to MIT-SHM. Fixes #255 #274 Signed-off-by: Yuxuan Shui <yshuiv7@gmail.com>