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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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WVL
Registered: Mar 2002
Posts: 902 |
Quote: @algo: would it work to flash an area in the non-visible part of the border? Stupid question probably, but I gotta ask just to be sure. ;)
it would, as long as the pixel-mask of the screen gets hit by the electron beam.
The reason the screen distorts when the brightness changes is that the pixel-mask changes temperature (because of more electrons hitting the mask if brightness increases, and thus getting hotter) and deforms. This is why CRT-screens with pixel-masks made from invar (a special steel-alloy with the property of very low deformation around room-temperature) are the ones to be preferred :)
Then again, you can never be sure if you are hitting the mask or not, because monitors and tv's are so different, and then you can change the settings also!! OMG!
But probably it's possible to shift the screen vertically 0.5 pixel by changing a few rasters in the upper border from black->white (in that case the screen will move down) |
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Oswald
Registered: Apr 2002
Posts: 5094 |
wvl, thats quite hard to believe , as on some old and/or bad TVs the screen can distort a whole lot when white color is shown. I dont believe that an iron mask can jump up and down and sideways at 50fps according to the number of electrons. when I think about I'd rather say that the aiming of the beam goes off due to higher electron rates. |
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WVL
Registered: Mar 2002
Posts: 902 |
Quote: wvl, thats quite hard to believe , as on some old and/or bad TVs the screen can distort a whole lot when white color is shown. I dont believe that an iron mask can jump up and down and sideways at 50fps according to the number of electrons. when I think about I'd rather say that the aiming of the beam goes off due to higher electron rates.
It's really thermal expansion, and prolly you will not get 50fps from it, but maybe for a .5 pixel shift you can.. |
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Oswald
Registered: Apr 2002
Posts: 5094 |
then we are not talking of the same thing, I have wittnessed distortions like 1cm or 'tech-tech' on sluggish TVs when background went to white :) |
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WVL
Registered: Mar 2002
Posts: 902 |
Quote: then we are not talking of the same thing, I have wittnessed distortions like 1cm or 'tech-tech' on sluggish TVs when background went to white :)
Probably that's also thermal, but it takes a while until things stabilize completely. However I think some shadow-masks can wiggle around at 25fps for 0.5 pixel.
edit :
to stop the discussion I just simply tried it on my old trusty c64 and 1901 monitor ;) The screen jumps a little bit, but i can't make it jump 0.5 pixel, more say 0.2 pixels... :P |
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Oswald
Registered: Apr 2002
Posts: 5094 |
wvl, can you visualize an iron net making 1cm distortions coz of thermal stuff inside a tv at 50fps?:D |
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