Open bottom border in high resolution?

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BlankVector
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Open bottom border in high resolution?

Post by BlankVector »

When using ST-High video mode on modern VGA monitor, the image is aligned on top and there is a big black border at the bottom. I guess this is because the ST outputs a 640x400 signal, while VGA monitors expect 640x480.

After looking at overscan techniques there, I wonder if it would be possible to hack the ST-High to output more than 400 lines.

Any idea?
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troed
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Re: Open bottom border in high resolution?

Post by troed »

Not without messing up HSYNC. The exact position for a vertical "switch" in high resolution is the same position where HSYNC is generated.
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Re: Open bottom border in high resolution?

Post by ThorstenOtto »

It is technically possible, but not without visible artifacts. See also discussion in the german forum, where i tried to implement that as a TSR for GEM.

You would get a resolution with 480 lines.
Last edited by ThorstenOtto on Fri Sep 02, 2022 12:48 pm, edited 1 time in total.
czietz
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Re: Open bottom border in high resolution?

Post by czietz »

And since someone will invariably point out that there are a few demos that open the lower border in monochrome, let me point out that they cleverly hide the artifacts that troed mentions. As I wrote recently:

Patching the "Mono-No-Border Screen" demo (https://demozoo.org/productions/73157/) to run with an inverted screen, i.e., white background, explains what I meant:

Image

As you can see: Yes, it manages to display the scroll text below what would normally be the lower border of the monochrome screen. But it doing so, it massively messes with HSYNC, causing one very long line and, thus, very visible artifacts. You can see the analog electronics in the deflection circuitry of my poor SM124 slowly settling again during the next lines. [...] The demo just hides all that in the black background; but you can't use it with arbitrary programs.
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Re: Open bottom border in high resolution?

Post by BlankVector »

Brilliant.
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Eero Tamminen
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Re: Open bottom border in high resolution?

Post by Eero Tamminen »

The whole "Mono collection #01" was pretty nice. Except for two of the demos, all even worked with EmuTOS. "c64_show" did not work with Hatari GEMDOS HD emulation (maybe due to some issue in Hatari's handling of broken TOS binary relocation data?).
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Re: Open bottom border in high resolution?

Post by Nyh »

I_A of the TOS-crew experimented with the lower border in Mono too which resulted in the SM125 power blast. The line transformer of the Atari SM125 didn't like the messing up of the sync and burnt out killing the monitor.
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Re: Open bottom border in high resolution?

Post by elliot »

What about medium res?
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troed
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Re: Open bottom border in high resolution?

Post by troed »

elliot wrote: Tue Oct 18, 2022 11:52 pm What about medium res?
GLUE only deals in 50Hz, 60Hz and mono (71Hz) modes. Medium and low res are both either 50 or 60, so everything that can be done border-wise in low resolution can be done in medium resolution.
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Re: Open bottom border in high resolution?

Post by elliot »

I am sure it can be done but are there any examples?
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Re: Open bottom border in high resolution?

Post by troed »

elliot wrote: Wed Oct 19, 2022 12:32 pm I am sure it can be done but are there any examples?
As in released medium res overscan demos or example code? For the latter - it's exactly the same code as for low resolution. As to released medium res overscan then there are a few. Flix/Delta Force did a medium res fullscreen here: https://demozoo.org/productions/123968/
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Re: Open bottom border in high resolution?

Post by elliot »

Flix/Delta Force did a medium res fullscreen here: https://demozoo.org/productions/123968/
That looks so good, such high res. What is the end resolution? I wonder if the (vertical) rasters only go halfway across the screen so the rest of the scan line can be used for CPU time.

Okay, next question. Did anyone do a game/demo with split screen resolution (e.g. low res for game play then med for hud)? I am sure the STE is not too fussy about doing this (not sure about STF). I remember trying to do this in STOS but I can not remember the results, I think it ended with messy screen, not sure why.
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Re: Open bottom border in high resolution?

Post by thomas3 »

elliot wrote: Thu Oct 20, 2022 8:03 pm
Flix/Delta Force did a medium res fullscreen here: https://demozoo.org/productions/123968/
That looks so good, such high res. What is the end resolution? I wonder if the (vertical) rasters only go halfway across the screen so the rest of the scan line can be used for CPU time.

Okay, next question. Did anyone do a game/demo with split screen resolution (e.g. low res for game play then med for hud)? I am sure the STE is not too fussy about doing this (not sure about STF). I remember trying to do this in STOS but I can not remember the results, I think it ended with messy screen, not sure why.
Yeah, sure that some of the Magnetic Scrolls text adventures did this?
Incidentally, I wrote a STOS module that did it too (in ASM) - very simple code and works in STF or E.
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Re: Open bottom border in high resolution?

Post by elliot »

For me I did rasters, etc in STOS by waiting for a VBL (no timers) and then a FOR..NEXT until I wanted to change colours or res. This meant no time to do much else plus it was not that stable. Rasters looked poo unless they moved up and down which masked the imperfections.

My three channel shaded VU meters in the borders looked good though.
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Re: Open bottom border in high resolution?

Post by Nyh »

The drawing program GfA Atrist was for drawing in low-res but the menu was in medium res. I think GfA raytrace had a mode with a vertical spilt in low and medium res.

The main menu of the Demounstures demo which I wrote completely in Omikron basic has a low res smiley sprite, a medium res scroller and lots of rasters. :-) In Omikron basic you could disable all interrupts, sync with the beam and by very carefully writing your code stay synced so you can doo rasters all over the screen.
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Re: Open bottom border in high resolution?

Post by troed »

elliot wrote: Thu Oct 20, 2022 8:03 pm Okay, next question. Did anyone do a game/demo with split screen resolution (e.g. low res for game play then med for hud)? I am sure the STE is not too fussy about doing this (not sure about STF). I remember trying to do this in STOS but I can not remember the results, I think it ended with messy screen, not sure why.
The "vertical scrolling man" in {Closure} is in medium res, while the textwriter that scrolls up below it is in low res. It's thus a vertical medium/low rest split that sync scrolls, _and_ crosses the lower border opening position.

Was interesting to code.
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