https://github.com/ttsiodras/zx_spectrum_scrolling

Using Z80 assembly to perform screen scrolling (per-pixel)
https://github.com/ttsiodras/zx_spectrum_scrolling

Last synced: 4 days ago
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Using Z80 assembly to perform screen scrolling (per-pixel)

• Host: GitHub
• URL: https://github.com/ttsiodras/zx_spectrum_scrolling
• Owner: ttsiodras
• Created: 2022-02-15T20:21:54.000Z (almost 3 years ago)
• Default Branch: master
• Last Pushed: 2024-08-18T12:54:47.000Z (4 months ago)
• Last Synced: 2024-08-18T13:59:54.946Z (4 months ago)
• Language: C
• Size: 7.81 KB
• Stars: 0
• Watchers: 3
• Forks: 0
• Open Issues: 0
• Metadata Files:
  • Readme: README.md

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README

        
It was fun, writing this. Memories from childhood!

Click the image below to see the code run inside FUSE:

[![Scrolling per-pixel the Speccy's screen via Z80 ASM](https://img.youtube.com/vi/LsN2iZfjdZ0/0.jpg)](https://youtu.be/LsN2iZfjdZ0)

- Scrolling the top 2/3rds of the Speccy's screen

  one pixel at a time, via optimised Z80 assembly...

- ...and finally printing the achieved frames per

  second *(~23 running under FUSE; no idea what a

  real Speccy would score, but probably something

  close)*.

z88dk doesn't support macros in the inline assembly;

but it does support `m4`! So I [defined](scroller.c.m4#L5)

an `m4` macro to emit the bodies of the scrolling 

functions; their only difference being the direction

of the change to the `HL` register (`inc`/`dec`), and

the `RL`/`RR` instructions used to shift the bits.

Sigh... :-)

I can still remember my 13 year old self struggling

to understand how one could possibly scroll the 

Speccy's screen... It now only took me a couple of

hours to write this!

3 decades of coding definitely helped :-)