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Forums > C64 Coding > Ghostbyte / garbage / $3FFF
2008-12-05 11:57
Mace

Registered: May 2002
Posts: 1799
Ghostbyte / garbage / $3FFF

Discussion about the ghostbyte in the comment of Aliens:

Quoting Jammer
so 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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2021-03-05 16:55
Copyfault

Registered: Dec 2001
Posts: 467
Quoting Compyx
...
I think you can also set sprite priority so the ghostbyte will cover the sprites. Not sure about that one, I'd have to check that.
Can confirm, used it in some -yet unreleased- code ;)
2021-03-05 17:30
Krill

Registered: Apr 2002
Posts: 2854
You both seem to be ignoring or misreading what w4rp8 is implying here.

If i understand correctly, this is about glitching the rendering of the idle byte by just writing to seemingly unrelated colour registers, and that glitching causes it to be briefly rendered with black hires pixels in multicolour mode rather than black brick pixels.
2021-03-05 17:35
w4rp8

Registered: Oct 2010
Posts: 9
If it's not a bug in Vice. And the timing of the glitch seems to shift with the index of the color-register you write into.
2021-03-05 17:53
Compyx

Registered: Jan 2005
Posts: 631
Quoting Krill
You both seem to be ignoring or misreading what w4rp8 is implying here.

If i understand correctly, this is about glitching the rendering of the idle byte by just writing to seemingly unrelated colour registers, and that glitching causes it to be briefly rendered with black hires pixels in multicolour mode rather than black brick pixels.


And that would then display some multicolor pixels in a single 'char'?
2021-03-05 17:58
Copyfault

Registered: Dec 2001
Posts: 467
Quoting Krill
...
If i understand correctly, this is about glitching the rendering of the idle byte by just writing to seemingly unrelated colour registers, and that glitching causes it to be briefly rendered with black hires pixels in multicolour mode rather than black brick pixels.
Oh that sounds like "something new"... good point, will have to investigate deeper on this "feature".

Thanks for bringing it up, Warp8!
2021-03-05 18:10
chatGPZ

Registered: Dec 2001
Posts: 11148
I strongly suggest to try it on real hardware, and come up with a test program :)
2021-03-05 21:11
Krill

Registered: Apr 2002
Posts: 2854
Quoting w4rp8
If it's not a bug in Vice.
Yes, of course. That manipulation apparently only triggering line-wise responses makes it reek a bit like an emulation bug, indeed. And what Groepaz said. =)
2021-03-06 10:02
tlr

Registered: Sep 2003
Posts: 1727
I'm not sure I fully understand the description, but I'm assuming you're running x64sc right?
A simple screen shot of the effect would be a good start.
2021-03-06 10:26
Laurent

Registered: Apr 2004
Posts: 40


This is from a real c64 (so, same behavior as Vice)
Fresh has some explanation here GhostbyteInSprite
2021-03-06 10:33
tlr

Registered: Sep 2003
Posts: 1727
Quote:

This is from a real c64 (so, same behavior as Vice)
Fresh has some explanation here GhostbyteInSprite


If it's that, we have discussed it quite a lot here: Sprite data fetch in sideborder

From the description I thought w4rp8 referred to the screen area idle fetch graphics, not the idle part at the top of sprites.
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