Date   : Wed, 04 May 2005 10:13:31 +0100
From   : Richard_Talbot-Watkins@...
Subject: Re: BBC B/Electron Chuckie Egg queries

Peter Craven wrote:

> I was really looking forward to trying this listing - unfortunately,
> I have issues ... :(

uh-oh...

> I think I've correctly typed in your listing (including identifying
> the missing & on line 140, in your repeat listing) but I'm getting
> mixed results even tho I appear to have the same CH_EGG as
> you.  The Chuckie Egg logo on the title screen is corrupted in
> both MESS and BeebEm - is that right?

Yep, well spotted - it should be LDX#&27.  Also, the rest of the line
(after .q) was word-wrapped by Lotus Notes (bleugh), so obviously this
should all be on one line.  I've checked that listing against the actual
code I'm running and they're definitely the same.

Perhaps you have a different version of the executable - mine is from
http://www.stairwaytohell.com/bbc/archive/diskimages/AnF/ChuckieEgg.zip .

I've tested the patch on Model B (10-04-2004) and BeebEm 2.2, and it works
fine with both.  Don't know about MESS (but have never really trusted it to
provide as accurate emulation as a dedicated emulator).  Incidentally I've
found Model B to be rather more accurate than BeebEm with regard to
timing... it seems to run Chuckie a little smoother than BeebEm in any
case.

> Then, on playing the game in BeebEm - the background of the
> information at the top of the screen turns red (altho the font
> colour stays black, unlike the spectrum version) but the eggs
> stay yellow ... :/

Very odd - I can only imagine this would happen if your executable was
subtly different.  The only thing that should appear diferent at the title
page is the text 'HIGH SCORES' will appear in white rather than yellow.
Everything else will be the same.

>From a technical point of view, the patch works by modifying the colour
that eggs and lifts are plotted in, and changing its palette entry to
display white.  The red status is achieved with an interrupt which switches
the magenta palette entry to red at the top of the screen.  This isn't
ideal though as it requires a tiny extra bit of CPU which will alter the
timing of the sprite plotting a little bit (and lead to flickering in
different places to the original).  I've just realised there is a way to do
this which doesn't involve this interrupt trick, and I'll give it a go
soon... look out for Patch Version 2 (coming to a screen near you...soon).
This should also allow us to have different coloured digits for the score,
a la Speccy!

Good luck!

Rich


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