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SIDWAVE
Account closed
Registered: Apr 2002
Posts: 2238 |
D011 scrolling
Hi,
What is the best rasterline to flip the D011, when
scrolling the screen ?
No FLD!
Plain old scrolling ?
I have timing error, so the text jumps a bit.
Scroll the colorram too in same scan, takes a lot
of time..
Thanks for ANY help!!
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Oswald
Registered: Apr 2002
Posts: 5094 |
I bet that was horizontal hardware scrolling :)
just do a dec/inc d011 (or inc dec ? cant recall) on the last top border rasterline, and the 1st column of the screen will start where you do the trick, needs cycle exact timing. |
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Stingray
Account closed
Registered: Feb 2003
Posts: 117 |
Thanks, sounds like you get horizontal scrolling by inc/dec vertical scroll bits. Have I got that right cause that sounds pretty freaky. So you just chuck new bytes down either far left or far right (depending on which way you are scrolling) column of the screen once you've scrolled eight bits?
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Oswald
Registered: Apr 2002
Posts: 5094 |
here is how it works:
http://www.minet.uni-jena.de/~andreasg/c64/vic_artikel/vic_arti...
generally it juts moves the place of the first column of the screen, and the screen will wrap around, so before the first coulmn you get the last. |
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Oswald
Registered: Apr 2002
Posts: 5094 |
oops, I thought the link will jump to the right place, but it does not.
read under:3.14.6. DMA DELAY |
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Stingray
Account closed
Registered: Feb 2003
Posts: 117 |
Thanks, had a quick read of it, sounds pretty complex to. If the screen can only wrap around I can't see how it could have been used in a game like Mayhem, unless there is a way of changing only the bytes in the first or last column. Even if it's not the trick they used it's still pretty freaky. |
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CyberBrain
Administrator
Posts: 392 |
DMA DELAY has often been used in the good old wanker-effect. You know... Where you move a logo left/right by a sinus movement. It's called wanker-effect because the movement looks like.. err... wanking. (if you use double-sinus it looks like drunk wanking) |
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Puterman
Account closed
Registered: Jan 2002
Posts: 188 |
For more advanced wanking techniques, please consult the ever popular Wank Article. |
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AmiDog
Registered: Mar 2003
Posts: 97 |
Well, not that I know what I'm talking about but anyway. I assume that by using DMA delay, one only need to copy 25 bytes rather than 1000 when scrolling a "full column"? I.e. replace the column which wraps? |
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Oswald
Registered: Apr 2002
Posts: 5094 |
stingray: the explanation is complex, the theory codewise is simple: do a dec d011 inc d011 on the last top border rasterline in the middle of the screen with a straight irq, and you will see how it works.
or to explain it in another way:
lets say the screen has just 10 columns:
default state:
0123456789
dma delay:
dec d011
inc d011
\/
6789012345
to update the screen you just change the columns that are actually at the leftmost, rightmost on the screen.
amidog: right. |
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Oswald
Registered: Apr 2002
Posts: 5094 |
ofcourse csdb was "wise" enough to remove the necessary spaces.. argh.. once again:
dec d011
inc d011
____\/____
6789012345 |
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