sassquad
Posts: 5
Joined: Sat Oct 20, 2012 12:45 am
Location: Godalming, Surrey
Contact: Website

RISC OS Sprite Handling

Tue Dec 11, 2012 2:45 pm

Hi there,

I put this out on the RISC OS Open Forum last week, and am putting it here, in case anyone has missed it.

Some of you may or may not be aware that my brother and I wrote a couple of RISC OS games, which have been updated sporadically over the years.

Having managed to get RISC OS Pi installed and running successfully, I had a go at running these games. It didn’t take long to discover that they didn’t work.

I cannot vouch for whether sound works, as I’m using an HDMI>DVI converter for my monitor, and have not plugged in earphones as yet, but sprite handling, screen banking and 16 colour (4bpp?) display is an issue.

I’ve prepared a live document of all the bits and pieces of disparate information available concerning the use of RISC OS' sprite commands, mode independence, and screen buffering, in order to get some sort of definitive article on converting said games to the Pi:

https://docs.google.com/document/d/1Eca ... U-Jd0/edit

I am aware of efforts such as the JASPP, which are going great guns with commercial software releases, as well as the use of ArcEm on the Pi to run said games. I would prefer however, to get my games to run natively on the Pi. :-)

I’ve had some progress in doing colour mapping of 4bpp sprites (with palettes), but have hit issues with display tearing/flashing concerning the screen swapping, a technique used a lot in RISC OS games. I would welcome contributions to my living document, free for anyone to edit, on how best to address:
  • sprite handling
  • resolution independence
  • screen swapping
There’s arguably some degree of interest in getting legacy games (whether it’s freeware, public domain, subscription discs etc.) to run on the Pi, and all this information needs pulling together somehow.

(11 Dec update) – I’ve reorganised the document in an attempt to get some clarity on the above sections, as well as add some more links concerning mode/resolution independence and screen swapping. I can see the document has been viewed many times, I hope it is proving of some use to people :-)

Please, if there is anything on there that doesn’t make sense, or is just out and out wrong, either let me know, or edit it accordingly.

Thanks in advance! :-D

Stephen Scott
http://www.sassquad.com/riscos
Stephen Scott, SAS Squad Digital Media
www.sassquad.com

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