Posted By
Fuzzweed
on 2024-12-01
13:07:51
|  Changing ff06 mid screen
Is it possible to update ff06 vertical scroll position mid screen? Everything I've tried it seems to go crazy jumpy rather than a little tear.
Obviously it could be my noob skills, or maybe it's just something that can't be done neatly?
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Posted By
Csabo
on 2024-12-01
13:30:28
| Re: Changing ff06 mid screen
Definitely, but it's not trivial. If that helps, you can take a look at games like Legionnaire, or any similar games that implement vertical scrolling only on part of the screen. In YAPE you can add a breakpoint such as "B FF06 W" to stop any time $FF06 is written to.
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Posted By
Fuzzweed
on 2024-12-01
14:33:54
| Re: Changing ff06 mid screen
FF07 worked easily. Set one value at the top and another after the split, so I guessed FF06 might be harder because it didnt like the same trick.
Is it a timing thing? It can only be changed at the start of a whole chr block or something...
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Posted By
gerliczer
on 2024-12-01
14:55:03
| Re: Changing ff06 mid screen
Two thoughts. IDK if they will help at all. 1) It is never a bad idea to do raster tricks with stable raster. If you did not do it yet, look it up in the forum. There is at least one example code there, IIRC. 2) $FF06 is the tool to trigger badlines. Careful with that.
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Posted By
Fuzzweed
on 2024-12-01
15:03:14
| Re: Changing ff06 mid screen
Thank you. I will check it all out
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Posted By
Murphy
on 2024-12-01
16:46:37
| Re: Changing ff06 mid screen
The display of a line depends on several registers that you have to keep in sync. It has been discussed previously during the development of The Pit. You can find tips there.
Forum (#35837)
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Posted By
Fuzzweed
on 2024-12-01
17:49:49
| Re: Changing ff06 mid screen
Got it. It might be something I try and avoid on current project  but its a good explanation, thanks.
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Posted By
Charles
on 2024-12-02
00:24:55
| Re: Changing ff06 mid screen
I struggled with this myself, but yes you can do it. You need to adjust $ff1f right after setting a different vertical scroll value in $ff06. If you can't figure out I can share a working code sample.
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Posted By
Fuzzweed
on 2024-12-02
04:06:42
| Re: Changing ff06 mid screen
A code snippet would be great - or actually just a fuller explanation of how the new ff1f value is calculated from the new ff06 (and the split line location??). I like to figure things out, but im quite tight on time, its supposed to be an xmas demo
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Posted By
gerliczer
on 2024-12-02
04:51:55
| Re: Changing ff06 mid screen
My guess would be that you need to increase $FF1F value by the amount of vertical shift you introduce through the $FF06 change. But that would cost next to nothing to try all eight possible values.
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Posted By
Fuzzweed
on 2024-12-02
06:02:18
| Re: Changing ff06 mid screen
Ha, I take your point. But you should remember I've only been using 6502 for a few weeks. I'm still at the stage where if something works it could be lucky accident. It's much more helpful to know how it *should* work and then at least I can compare my attempts and work out if I got it right by design or fortune.
What I mean to say , is 'just try it' is how I like to work, but so far to try one thing takes about 2 days work :)
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