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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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Jammer
Registered: Nov 2002
Posts: 1335 |
thanks a lot! i play with kick assembler recently so i have to try it out :) |
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algorithm
Registered: May 2002
Posts: 705 |
It does not need to cover the entire width of the screen. Just like horizontal color splits you can change the ghostbyte half way through etc and combine with $d016 etc. A camelot demo and some crest demo's use similar methods |
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Graham
Account closed
Registered: Dec 2002
Posts: 990 |
Also it's not always at $3FFF, depending on the VIC-bank selected it can also be at $7FFF, $BFFF or $FFFF. And if you enable ECM mode it can be found at $39FF, $79FF, $B9FF and $F9FF.
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Mace
Registered: May 2002
Posts: 1799 |
Graham, of course... I was keeping it simple :-)
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Cruzer
Registered: Dec 2001
Posts: 1048 |
Quote: Also it's not always at $3FFF, depending on the VIC-bank selected it can also be at $7FFF, $BFFF or $FFFF. And if you enable ECM mode it can be found at $39FF, $79FF, $B9FF and $F9FF.
Guess that's why they invented the term "ghostbyte". |
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Oswald
Registered: Apr 2002
Posts: 5094 |
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? :) |
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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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