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Mace
Registered: May 2002
Posts: 1799 |
Ghostbyte / garbage / $3FFF
Discussion about the ghostbyte in the comment of Aliens:
Quoting Jammerso for what extent can i control this 'garbage'? in terms of chars and colours.
The ghostbyte is always black.
It occurs in the upper and lower border, when opened, but also in the 'void' that is created with an FLD routine.
If you want that effect as seen in Aliens, you have to write values to $3FFF in a raster routine.
The byte is repeated over the entire width and height of the borders, as the patterns shows.
BTW, I can't remember ever seeing a 'split raster' in $3FFF...
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pernod
Account closed
Registered: Nov 2004
Posts: 25 |
A fun thing is that when you do a transfer to RAM from a REU, you can lock the destination address counter, so $3fff gets updated every cycle ==> free (black + other color) hires gfx in upper and lower borders. Me and Mastermind/HZ played around with this back then.
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Mace
Registered: May 2002
Posts: 1799 |
Well... I found that byte myself too, but I was 2 years older and never exploited the possibilities :)
But boy, was I pleased that I finally got that garbage away in Get Life+! |
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Oswald
Registered: Apr 2002
Posts: 5094 |
yeah, my initial goal was to get rid of the garbage too :) |
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Skate
Registered: Jul 2003
Posts: 494 |
@Oswald: Same here. When I opened upper/lower borders for the first time, I've met with this "bug" personally. I found the address causing this irritating "bug" by clearing random memory addresses. I was so happy when it's gone. I've never thought of anything useful about it. :) |
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Ksubi
Account closed
Registered: Nov 2007
Posts: 87 |
My favourite ghost byte piece of code from 1987: Gauntlet the intro by the Cult is simple and cool. |
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JackAsser
Registered: Jun 2002
Posts: 2014 |
I think Graham made the coolest application of it so far (C128 only though) in RFO - The VIC experience. If you open the top/bottom border and disable the screen at the same time u get the classic sprites+3fff without chars screen. On a C128 in 2Mhz mode the VIC will never issue any memory reads so the $3fff-gfx every VIC-cycle is now instead what was left on the bus, i.e. the bytes that was read by the CPU. So, by using 2c op-codes, like f.e. LDA #$xx u can indirectly alter the $3fff gfx every VIC-cycles by simply align the CPU-read of the immediate value and the VIC. Kinda cool! :) |
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Mace
Registered: May 2002
Posts: 1799 |
JackAsser... can you translate that to a language I understand, please? :D |
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Danzig
Registered: Jun 2002
Posts: 440 |
Quote: and to further extend this exciting coder dick size compo: I have found the ghostbyte myself when playing with a ripped fld routine being 14 years old, even made these pattern effects with it. anyone has better bets? :)
you explored it yesterday? that makes dick size * -1 ;) |
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Zyron
Registered: Jan 2002
Posts: 2381 |
Quote: JackAsser... can you translate that to a language I understand, please? :D
You can make cool effect! ;) |
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Hein
Registered: Apr 2004
Posts: 954 |
There is also simple but practical use, I used it in The Good, the Bad and the Ugly with split raster to create a lovely black rectangle in the top border. |
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