If im correct the C Demo Scrolling trick uses the method were you draw behind and in front creating an identical image like this
http://eab.abime.net/showthread.php?t=80646or for horizontal and vertical -
and no corkscrew is used ive only ever done 8 way scrolling like this and yes scrolling down right is the ultimate test - if you view the entire Bitmap save it as iff not just what is displayed on screen ie something like 640 *480 you will see it split into something like 4 identical pictures - when full scroll down right.
There must be a fairly simple formula for this something like screen width, height = number of tiles that must be drawn and height and width bimtmap must be to complete perfect down right scroll.
I never figured it out the formula and no one has ever published it to my knowledge I just guessed and worked on overkill to make sure I drew enough tiles etc.
and as you know Blitz has problems InitCopList corkscrew past 8191
