Originally Posted by pmc
This might be my misreading but are you saying you can do only four blits per word and still get a 1 pixel resolution sinescroller?
blit up and down with a mask. first mask covers all columns that have to go down 8 pixels. next cover all columns that have to go up by four pixels, then up by 2, then up by 1. as long as the slope never exceeds 1:1, this is sufficient.
example: first mask = $FF00, second mask $0F0F, third mask $3333, fourth mask $5555, this would give a straight 1:1 slope.
to calculate the values of the masks, do a quick "chunky-to-planar" type conversion on the y-data. (Could precalculate all these)
sometimes it is useful to think deeper inside the box.