Date   : Tue, 10 May 2005 14:13:49 +0100
From   : Richard_Talbot-Watkins@...
Subject: Re: Beeb versus Master?

Richard Gellman wrote:

> Christopher Dewhurst CCARE Panel Clerk wrote:
>
> > And access to OS1.2 or Basic I/II ROM routines and tables.
> > For example, the 640x table for sprite plotting in Modes 1
> > and 2 (only in the BBC B's OS1.2), and the 'warm start'
> > routine in the Basic Rom.
>
> Sprite plotting? *impressed* Of which, did anyone else ever
> make use of the SPRITER ROM image on the Master Welcome
> disk?

The 640x table in OS1.20 was just a quick way of looking up 640*x where x
was a screen row number between 0 and 31.  The OS used it to obtain screen
addresses of the start of character rows, as it was a little quicker than
doing the multiplication by 640 'by hand'.  This would then be used as part
of the calculation to calculate a screen address for the text output code.
There was no actual sprite plotting code in any of the OS versions.

Because it was there, sometimes it was also used by games coders to help
speed up the screen address calculation.  Frak! and Castle Quest were two
culprits - the effect of running these on a Master is that all the
characters appear near the top of the screen (because the 'table' is
returning values of 0 for each index).

I used to find the Spriter ROM *very* useful.  I did all of my sprite
design for games with it - it was handy for knocking up quick Basic
programs to test animations and things, and then made it very easy to
convert them to a 'raw' format, for use in my game (with a 'proper' sprite
routine).  It may not have been the fastest or most easy-to-use editor, but
it was versatile and it worked!

> > This may be true for games software (re-)released in the late
> > 80s/early 90s but not all. In fact some of my favourites in the
> > Ultimate Play The Game range like Sabre Wulf haven't (yet)
> > been patched satisfactorily to run on the Master. But if your
> > main use of the machine is not for games playing this isn't TOO
> > much of an issue.

I had all the Ultimate titles working on my Master - all except Alien 8
whose protection I just couldn't crack.  The usual problems were their use
of chunks of OS1.20 code to change screen mode without clearing the screen,
hard wired OS1.20 IRQ routine exit points (JMP &DC93), and assuming that
the character set definitions lived in the ROM at &C000...&C2FF so they
could plot characters directly, rather than using OSWRCH.

> When I say "all" I mean a generic "all". Yes, there are some out
> there that still don't work properly on the M128, but most of the
> popular games we're re-released as master-compatible versions
> (or in some cases, such as Stryker's Run, Master-Enhanced versions.
> In this case, the BBC B version doesn't run at all - except for the
> later re-releases (compilation releases?) which seem to be
> re-recoded).

Yep, most games which got a re-release (e.g. as part of a Play It Again Sam
collection) were fixed to run properly on the Master, for example Zalaga,
Citadel and Frak.


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