use -DOFF_SMOOTH to omit following page buffering

[Apaczer]

• increases image swapping time with minimal RAM on target platform
• use get_page_bottom() to differentiate page size height
• change to start page with PAGEDOWN/UP keys

Still I can't figure out how to adjust bottom line correctly for prv page when change_page(-1). Otherwise it works really well on those weak devices with little available memory.

[rofl0r]

OFF_SMOOTH is kind of a misnomer. OFF is generally associated with "offset". a more suiting term would be DISABLE. but i'm generally not a friend of littering the code with ifdefs. it would we nicer if one could simple override RENDER_PAGES which defaults to 2 if not already set, and optimally it would even allow greater values than 2 to make the program behave well even in such a case. though here in order to make progress as quickly as possible, i'd suggest you first throw out all code that renders the second page - make heay use of gdb on your desktop to inspect the values live, which helps a lot to figure out what actually happens - and once you got everything behaving as you desire, make a diff and then look how you can cleanly integrate the changes into "upstream". or you just decide to make a hard fork with "smooth scrolling" removed.