PocketFrog - backbuffer

Hello,
I'm new to PocketPC programming. I've chosen PocketFrog for making a PocketPC port of our Symbian Series60 game ATOMIX.
I've got one small question:
Is it necessary to blit all the scene every frame or can I be sure that the content of backbuffer is unchanged since the previous frame?
Thanks
Tomas
I'm new to PocketPC programming. I've chosen PocketFrog for making a PocketPC port of our Symbian Series60 game ATOMIX.
I've got one small question:
Is it necessary to blit all the scene every frame or can I be sure that the content of backbuffer is unchanged since the previous frame?
Thanks
Tomas