Vertical Rupture Scrolling Mode 5 by Richard Broadhurst (tricky)
Demo of how to use rupture to scroll a mode 5 screen a pixel at a time vertically in BeebAsm.

Sorry for the poor upload, but I don't have much time.

This demo is an implementation of an idea I had this week.

I was thinking that I would really like to port an old side scroller, but if I couldn't get it smooth, why bother; that was when I re-read RichTW's rupture article and thought "Why not just turn the screen on its side like in the old arcade cabinets?" This should be possible with new rotating monitors (or even old cub ones).

While I was thinking, I had an idea for drawing backgrounds efficiently by drawing a couple of pixels rows each frame.

I had to fiddle about quite a bit and use the source code of B-em to see why my rupture wasn't working as it should. The main problem is that to have one large screen, the other needs to be very small and this leads to tight timing requirements or the whole thing doesn't work.

My beeb is still packed from my move, so I have only tried this on Beebem and b-em, but in theory it should be ok.

I will try to update the Graphics Sample entry when I have more time to explain how it works, but if anyone feels inspired to use it for a game, it should use less than 10% of the frame to draw the background and uses 1 byte for a 16 pixel (8 doubled) high square sprite in its map. The initial code only allows 32 different tiles, but with a small change, that could be increased to 64 with no increase to the maximum time per frame.

Hehe nice. That game looks familiar

Never whent back to this, as I started carnival, but have uploaded a video for those on the move http://youtu.be/w5ATw4Z5id0