dirrerence between cairo and GDK as to drawing

[Randy <randyqiuxy hotmail com>]

Hi list,
I plan to draw complicated graphics(interpret a new format file and
render it to the screen) via GTK+ and it needs a good display speed.
I find most GTK+ books or references mentions less about drawing than
widgets descriptions.Anyone could give me some info about it?
I only know the cairo is now a part of GTK+,but I don't know how I
should make such a choice---use cairo or Gtk's relative functions,when
I'm going to do my work mentioned above.
Any suggestion?
Thanks for your time!

Best regards,
Randy