Hardware Blitting in GTK+

[Rashid <rashid milacom de>]

 hi guys i want to do the following: i got a freerunner smart phone. it
can use accelerated blitting. its working and its fast but only under
xlib not under sdl (sdl 3 frames per second, xlib 50). 
  but xlib doesnt support an alpha channel (and the freerunner has only
16 bits per pixel). is there an easy way to do transparency (one
transparent color is enough) with xlib or a toolkit which builds an
xlib?
 can i blit in gtk+? with a transparent color? in sdl it works
 but sdl isnt hardware accelerated with blitting in X11.

if there a few tips for double buffering i would be happy to :)