Meltdown programming tricks

Subject: Meltdown programming tricks
From: "Thomas Jentzsch" <tjentzsch@xxxxxx>
Date: Wed, 25 Aug 2004 12:54:27 +0200
I don't know if anybody else has already looked into the Meltdown
code. I got curious because it doesn't work perfect on emulators.

The code is IMO quite sophisticated:
1. It uses selfmodifying code for kernel display!
2. It uses flicker for some quite effective anti-aliasing
3. Is uses a trick which is new too me to display two wide spaced
AND double size players! Here is the code, which I suppose is 
responsible for that:
  009e: ldx #04      ; two copies wide
  00a0: lda #35      ; double sized player    
  00a2: stx  NUSIZ0  
  00a4: sta  NUSIZ0  
  00a6: lda #15      ; double sized player    
  00a8: sty  GRP0    
  00aa: stx  NUSIZ1  
  00ac: sta  NUSIZ1  
(AFAIK you can ignore the bits for missile size)

So by switching the register to two wide copies and *immediately* 
after set switching to double size player, you seem to be able to 
combine both settings. Isn't that cool?!?

Maybe it is also possible to combine other settings (e.g. quad size player
and three copies wide) by using this trick. I'll start experimenting with 
that when I return home.

Have fun!
Thomas Jentzsch         | *** Every bit is sacred ! ***
tjentzsch at web dot de |
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