Date   : Thu, 29 Sep 1994 15:55:35 +0000
From   : lamcw <lamcw@...>
Subject: Re: CRTC and ULA emulation

James B. wrote:

;Many games use split palette modes, but I can only think of the above two for
;changing screen modes. Maybe Sphere of Destiny does. Speaking of S.O.D, do
;people realise that the speed (it's a "trailblazer" clone) of game is simply
;because the animation of the 3D trail is done purely using colour palette
;switching? Amazing! Exile also uses colour palette hacking (for the water), as
;do many other games I imagine.

i'm afraid i've never seen SOD or Exile (shock horror). maybe someone out there
will loan me a copy... you'll get it back, honest!

i remember a Trailblazer game for the Atari 8 bit machine and it went like the
clappers.

;It depends on precisely what they're changing. The mode in FE20 is simply the
;colour control (ie bits per colour) isn't it? If the resolution changes (eg
;mode 4 vs mode 2) CRTC registers will surely need modifying. I'd be suprised
;if Elite didn't do this somewhere, although I can't remember the modes it uses.

yep, could be right.


Revs is sneaky. heres how the screen looks like:-


3 lines MODE 4 - for time and best time

7 lines of apparent garbage

about 18 lines of MODE 5 for the track + car display


when i saw all that garbage, i thought it wasn't working properly. but i then
realised that it was PROGRAM CODE!!! a video interrupt zaps all the logical
colours to cyan so it looks blank. then another video int zaps it to the 
colours needed for the MODE5 display. makes the Elite display look positively
simplistic!


chris lam.