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Rybags

New Demo release - MemoPad 480i

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Here's a kind of practical implementation demo of real interlaced mode on the Atari.

 

MemoPad_480i.zip

 

Contains XEX file, and a bootable ATR image. Real machine (with 40K or more RAM) much preferred for this program, since at this point no emulation support exists for Interlaced Graphics on the A8 (although the program is still usable)

 

Pressing Option during the demo speeds up the scroller. All other keyboard functions pretty much as normal - feel free to move about the screen and try the fonts out.

 

post-7804-1243347276_thumb.jpg post-7804-1243348060_thumb.jpg

 

Capture card shot, and photo from real TV above ^

 

The (kinda crappy) looking bitmap part at the top is also in interlace... the curved lines help a little to show the doubled vertical resolution.

 

Just like the real MEMO PAD on the old 400/800, you can move the cursor about and enter text. The editor screen is split into 4 regions:

 

. A normal sized (gold) area which uses a 16 pixel high font in the normal space of a character.

. The red area uses a 10 pixel high font (compact)

. The green area uses a 8 pixel high font (mini)

. The blue area uses a 6 pixel high font (tiny)

 

The fonts are a bit of a rush-job. The 16x16 font in the scroller at the bottom is a modified version of the Plok (SNES) font. The 8x16 is a Serif Font I created based on the Atari default character set.

The 8x10 font is just a stretched version of the A8 default.

 

The 8x6 and 8x8 fonts are direct copies from the A8 charset in ROM, the 8x6 one is clipped and modified in places to fit.

 

The program has been tested on real PAL machine, and should work fine on NTSC although I only tested NTSC in the emulator.

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Can I get verification from NTSC people that it's working OK ?

 

Also, I didn't put any Field Swap mechanism in... it shouldn't need it (hopefully).

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Excellent work. Another good reason for me to finish the A8 mods to check this out.

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Works fine on my NTSC machine (via my S-Video to VGA convertor).

 

Stephen Anderson

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Great.

 

So we definitely can say, the A8 has 480i ?!

 

Someone should update Wikipedia ;)

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Same deal.

 

In a normal Atari display, you only ever see one set of scanlines occupied. In interlace, we populate even/odd on alternating fields.

 

Of course, so far as graphics go, you can simply elect not to bother enhancing certain objects. That just means the same pixel data gets displayed in the offset scanline for that object.

 

Or, if you want the enhanced resolution, you just supply different data so it gets used. In theory, you could have a doubled resolution bitmap, couple of lines of text which aren't enhanced, and PMGs at double resolution overlaying anything you choose.

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I was actually thinking along those lines the other day.

 

Except do it with the background/foreground stuff swapping positions each field.

 

So you have on the even fields:

BG stuff

<blank>

FG stuff

<blank>

 

Then odd:

<blank>

FG stuff

<blank>

BG stuff

 

Another idea is to see if APAC/TIP type pics can be made to look a bit better. Might try that a bit later today.

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I was actually thinking along those lines the other day.

 

Except do it with the background/foreground stuff swapping positions each field.

 

So you have on the even fields:

BG stuff

<blank>

FG stuff

<blank>

 

Then odd:

<blank>

FG stuff

<blank>

BG stuff

 

Another idea is to see if APAC/TIP type pics can be made to look a bit better. Might try that a bit later today.

 

so we have a gtia pixel with a 8:1 ratio now? :)

 

and the PAL trick of "interlacing" gtia 11 and 9 lines to get 256 colors works in some way?

 

NRV

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ok. got it running on my oldschool 130xe plus sony 40cm tv-set pal. it runs perfect without rolling pic but the tiny text is hard to read due to the interlace.

 

the first text seems to be perfect for it but not the small ones? so I would expect that pics look best... the mode reminds me Amiga interlace modes on my 1084... ;)

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With interlace, the rules re plotting vertical lines also apply in a way for horizontals, ie 2 pixel thick will look better.

But with characters, you probably want at least 10 pixels high to do so successfully - equivalent to 5 normal pixels high.

 

The smaller character sets are just direct copies of the inbuilt charset trimmed to fit.

 

The ideal character set would probably be 12 pixels high - equivalent in height to 6 normal pixels.

That height also gives you a 40x40 display at full screen size.

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memt617.zip

 

This is a modified testing release that Candle has requested.

 

It seems some LCD TVs have trouble with running interlaced screens (and normal Atari displays as some people have reported in other threads).

 

This version is essentially the same as the on in the original post except the use of Console keys. The setting 0/1 (off/on) is displayed onscreen for each.

 

START - toggles whether interlace mode is actually used

SELECT - turns field swap on/off, ie the character set display order will be reversed.

OPTION - enables/disables character set swapping.

 

 

Re the problem with LCD TVs/monitors - it is possible to use my method to get the Atari to create a VSync pulse train that more closely approximates what the "standard" is. My method at this time doesn't create the pre and post equalisation pulses which is missing from the Atari's video signal.

 

I've measured Commodore Plus/4 and C-64 with the 'scope. They both produce VSync pulse trains that more closely match the expected standard than Atari does.

I'd suggest to anyone who has problems running Atari on their LCD monitor - if you also have a Commodore 8-bit machine, try it also and see how it goes.

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Rybags, i'm shocked.

 

The original Memopad 480i works perfectly on my 1500XL Laptop's Display :-D

Edited by Beetle

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Cool. The later one should be fine too - it's just a modified one that lets you control those parameters for testing purposes.

 

I'm going away tomorrow for a few days, but I'll try and get a couple more bitmap picture examples done late in the weekend.

 

 

ed - Beetle: It would be cool if you could take a picture and put it up.

Edited by Rybags

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