A
frame buffer graphics device is an
idealization or
abstraction of your
computer's
video hardware in order to make
programming it simple. It
simulates or provides in actual
memory a space which maps to the
screen byte for byte (or
word for word, or
32 bit longword for longword), in such a way that the
data at
offset 0 stands for the
pixel at
coordinate (0,0), and so on until the end of line 0 (which has, for example, 1024 pixels), so that byte 1024 represents (0,1), etc.
This makes
creating graphics
off-screen easy, since you only have to
allocate and write to a
memory block of the same size as the frame buffer, and then copy the off- screen buffer into the frame buffer.
Frame buffer devices may fulfill more
complex tasks, but the thing here is the minimum.