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nikoniko
Account closed
Registered: Dec 2006
Posts: 1 |
New video modes? 320x400 and 160x400
Hi all,
Hydrophilic/Hydradix over at the Commodore 128 Alive! forums has been working on a technique to achieve 320x400 and 160x400 interlaced modes on a C128, taking advantage of the VIC IIe's undocumented test bit to allow fine control of raster output. He's succeeded in getting it to work for NTSC (at least on his own TV), and has now put up a simple demonstration and instructions on fiddling with the settings. Anyway, with some experimentation it sounds like it could turn into something pretty cool, especially if some bright minds here could combine it with other techniques.
I know this place is mainly about 64 coding, but since the approach should also work on 128s in 64 mode, I thought you might like to know about it.
Here's his announcement: http://landover.no-ip.com/128/viewtopic.php?pid=2637
And here's his webpage, which goes into some detail about the technique: http://www.geocities.com/hydradix/C128/Interlace.htm
And finally, here's the original forum discussion while he was working on it: http://landover.no-ip.com/128/viewtopic.php?id=807
I believe he's tried to make it easy to tweak, so PAL support could probably be achieved by someone who wants to play with it.
I'd recommend that if you want to ask him questions, the forums I linked to are probably the best place since he's a frequent poster over there.
Cheers,
nikoniko |
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JackAsser
Registered: Jun 2002
Posts: 2014 |
Quote: afaik, only works with (up) scrolling, otherwise you only get "more" colors, but not better resolution.
This trick with upscrolling is indeed used in many demos (for the endpart), shamefully i cant name a single one atm
@Yago: AFAIK my bro did it first in the end scroller of The Last Tracktor III.
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Cruzer
Registered: Dec 2001
Posts: 1048 |
Steppe is right, this is what was done in Krestage 2, and other did it even before this, e.g. Camelot :) |
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AmiDog
Registered: Mar 2003
Posts: 97 |
There's now a PAL compatible demo released.
Have a look here and check the forum here.
I've only tried it with my PAL C128 and 1084 monitor, but I have found some settings which produce an interlaced image. |
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Fungus
Registered: Sep 2002
Posts: 686 |
I saw a c64 demo with this technique done, I think it was released by Onslaught??? Scrolling some anime girl around.
As for the test bit things, Crossbow and Graham released Risen From Oblivion , which of course is exploiting this same test bit thing :)
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Oswald
Registered: Apr 2002
Posts: 5094 |
there is a demo called "400" which does a vertical interlace,... I dont really beleive to these theories that every 2nd frame moved and laced blah, aint the VIC hardwired to display its gfx on always the same lines on the tv? |
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MagerValp
Registered: Dec 2001
Posts: 1078 |
Quote: there is a demo called "400" which does a vertical interlace,... I dont really beleive to these theories that every 2nd frame moved and laced blah, aint the VIC hardwired to display its gfx on always the same lines on the tv?
Yes, the trick is that when you're scrolling 0.5 pixels per frame. If you scroll a non-interlaced image 0.5 pixels per frame, you get line numbers like:
frame 0: 200
frame 1: 199.5
frame 2: 199
frame 3: 198.5
Which the VIC can't display, as it can't move half lines. But if you scroll an interlaced image 0.5 pixels per frame, you get:
frame 0 odd field: 200
frame 0 even field: 199.5 + 0.5 = 200
frame 1 odd field: 199
frame 1 even field: 198.5 + 0.5 = 199
With scrolling plus interlace, the even fields end up on integer line numbers, which the VIC can display. As soon as the image stops moving, the effect stops working. It also works with 1.5 pixels per frame, etc.
Try it on a real C64 and you'll see that it looks great.
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Style
Registered: Jun 2004
Posts: 498 |
actually, depending on the monitor you might be able to shift the screen vertically in a subtle way simple from what youre displaying.
We've all seen it - you have some text on a black screen, then you change the background to white and the text shifts......
Monitors are teh crap :) |
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ptoing
Registered: Sep 2005
Posts: 271 |
So this only works with constantly scrolling stuff?
Would it be possible to scroll up and then flick down again and scroll back up or something to get "still" images to work. THAT would be neat. |
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Oswald
Registered: Apr 2002
Posts: 5094 |
Quote: Yes, the trick is that when you're scrolling 0.5 pixels per frame. If you scroll a non-interlaced image 0.5 pixels per frame, you get line numbers like:
frame 0: 200
frame 1: 199.5
frame 2: 199
frame 3: 198.5
Which the VIC can't display, as it can't move half lines. But if you scroll an interlaced image 0.5 pixels per frame, you get:
frame 0 odd field: 200
frame 0 even field: 199.5 + 0.5 = 200
frame 1 odd field: 199
frame 1 even field: 198.5 + 0.5 = 199
With scrolling plus interlace, the even fields end up on integer line numbers, which the VIC can display. As soon as the image stops moving, the effect stops working. It also works with 1.5 pixels per frame, etc.
Try it on a real C64 and you'll see that it looks great.
I dont understand it. but anyhow this is vodoo in my eyes. the vic always uses the odd (or even?) lines, and that is that. check the "400" demo in vice, how come it works even on a lcd screen (I have that)? you say IF the vic scrolls at 0.5 pixelfs / frame, yeah sure, but how? it cant. |
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ptoing
Registered: Sep 2005
Posts: 271 |
I think that technically it's 2 pictures and the picture is 400 pixels tall, but only the odd or even lines are shown, that's what they mean with 0.5 pixels i think. Not too sure tho. |
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