Here is a demo of how to scroll a mode 7 screen a pixel at a time vertically (uses BeebAsm).

The description is on the Sample Code page http://www.retrosoftware.co.uk/wiki/index.php/VerticalScrollingMode7

Please feel free to comment here.

ooh, that's strangely hypnotic ...

Sam.

Here is the corrected code with nice scrolling!

I added the unroll x3 and had to add a couple of RTSs as the old ones (return and retern) were no longer in range!

Even more hypnotic now

Moral: don't set A to what you need and then call vsync_wait to splat it!

[Edit] Premature optimisation of the 3 loads and 2 stores prior to the draw_map call!

30 downloads and no more comments - is everyone sat Mesmerized in front of their Beebs

Indeed.......

It seems that I just love replying to myself!

I thought that I should mention that this doesn't actually hardware scroll the screen, it redraws the whole screen every frame, that is why some can be left un-scrolled (if desired) and why it takes nearly 1/50th of a second to draw a frame.

If you watch for a while, you will see some parts of the screen have bits that change as they scroll down, this is where the values being read by the program change each frame, either because the OS is changing them or because they are being read from HW that has different values each frame (eg timers).