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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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Mace
Registered: May 2002
Posts: 1799 |
LOL @ Zyron :-) |
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Krill
Registered: Apr 2002
Posts: 2980 |
Mace: You do lda #$55 : lda #$f0 : lda #$0f and it shows this pattern: .*.*.*.*****........**** - fill a whole screen with it plus sideborder sprites and you have full-screen hires. |
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Mace
Registered: May 2002
Posts: 1799 |
@ Krill: ah, I see! Interesting. |
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Monte Carlos
Registered: Jun 2004
Posts: 359 |
Did you know, that the ghostbyte
in multicolor mode is behind / before
Sprites dependent on $d01d and the pixel combination
of a ghostbyte double pixel?
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Mace
Registered: May 2002
Posts: 1799 |
Monte Carlos, please rephrase... what do you mean with 'double pixel'? |
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Krill
Registered: Apr 2002
Posts: 2980 |
Mace: The idle byte is rendered with double-width pixels in multicolour mode. |
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Mace
Registered: May 2002
Posts: 1799 |
@ Krill: ah, I see! Interesting.
:-) |
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Cruzer
Registered: Dec 2001
Posts: 1048 |
Monte Carlos: ah, I see! Interesting.
Not sure what it can be used for, but always fascinating to learn something new about something you thought you knew everything about.
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Scan
Registered: Dec 2015
Posts: 111 |
Today I ran into something I think is odd. I've got the ghostbyte in a sprite when displaying it in the right side border from X position $68 and up. I get a line the width of a sprite a line above the sprite, of which the middle 8 pixels can be changed using the ghostbyte at $3fff. I've uploaded a demonstration here. GhostbyteInSprite Anyone an idea why this is happening? |
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w4rp8
Registered: Oct 2010
Posts: 9 |
I see, atleast in vice, that some bits of the ghostbyte could be masked by writing to $d020, $d021 ($d022, $d023 too, but not that stable without further stabilzising timing on the writes).
This works with unstable writes:
ldy color
lda #$27
!:cmp $d012
bcs !-
sty $d020
For such a line the ghostbyte goes from 0x33 to 0x21 without touching $7fff.
I saw this appearing in vice 2.4 only with 7 sprites enabled over that lines. vice 3.3 shows that behaviour, and also in areas without sprites enabled, but not as stable, more like writing to $d022. |
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