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chriz74
Registered: Apr 2009
Posts: 33 |
What is going on with those ghost bytes in the Ghost demo?
Can anyone explain what’s the catch? |
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chatGPZ
Registered: Dec 2001
Posts: 11116 |
Because only those 4 bits are connected to the databus at that time |
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Jetboy
Registered: Jul 2006
Posts: 213 |
Quote: Now? It was commonly used since the 80s really :) I wouldnt even be able to name another term for it right now *shrug*
We used to call it 3fff or 3ff for short. Or sometimes magic byte, but not very often. |
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Oswald
Registered: Apr 2002
Posts: 5017 |
Quote: Because only those 4 bits are connected to the databus at that time
VICII can read 12 bit at a time thats how it can read 40 char pointers and 40x4bit color in 40 cycles.
why would the 4 bits for color be connected to the char pointer bits part of the data bus when its FLI bug? |
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chatGPZ
Registered: Dec 2001
Posts: 11116 |
You'll have to ask the VICII designers. It's just what happens, it's an artefact of the DMA setup cycles. |
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Mr SQL
Registered: Feb 2023
Posts: 114 |
Quoting trident@frostbyte: if the ghostbyte would have been white instead of black, then "the frostbyte" would have been a pretty cool name for it :)
as to the op's question: this article has an explanation of the various ghostbyte techniques used in the demo: https://github.com/trident64/c64/blob/main/unexpanded-border-sc..
and a presentation on the topic from last year's fjälldata here: https://scenesat.com/videoarchive/93fbf2f3-aab5-11ed-931f-00505..
The Ghost actually uses a range of different ghostbyte techniques in the different parts, some use masking, some use a shine-through approach.
Great fjälldata presentation! Made it easy to understand with the demo examples and the slides. |
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Jammer
Registered: Nov 2002
Posts: 1289 |
Maybe 'trashbyte'? :D |
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chriz74
Registered: Apr 2009
Posts: 33 |
Ok I get it now but how do you make those ghost lines move along the scroller? |
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Jetboy
Registered: Jul 2006
Posts: 213 |
Quote: Ok I get it now but how do you make those ghost lines move along the scroller?
You ROL the ghostbyte synchronized with sprite movement. |
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Youth
Registered: Aug 2003
Posts: 40 |
Quote: You ROL the ghostbyte synchronized with sprite movement.
I remember doing a '40' char scroll in the border with this trick in Before You Go (part 3). I hadn't seen the effect before, but I doubt this was the first time. |
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ChristopherJam
Registered: Aug 2004
Posts: 1378 |
Trident - thanks so much for that article. The "Multicolor Ghostbyte Shine-through" technique finally makes sense to me :) |
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