TT Software overscan?

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mrbombermillzy
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Re: TT Software overscan?

Post by mrbombermillzy » Thu Jun 07, 2018 6:16 am

mrbombermillzy wrote:
Wed Jun 06, 2018 8:50 pm
Reducing the vertical scanrate would give some extra bandwith for horizontal pixels,
Oops! Excuse my gobbledigook facts above. Severe lack of sleep has caused me to fantasize that the TT is capable of 1280x960 in colour! :oops: lol!

The rest of what I said should still be reasonable folks. I will try not to think too hard next time. :lol:

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Re: TT Software overscan?

Post by Petari » Thu Jun 07, 2018 8:06 am

mrbombermillzy wrote:
Wed Jun 06, 2018 8:25 pm
...
Ray has done a demo which displays 1280x960 with 32 colours per scanline.
I havent had time to analyze the code, (theres no source code provided unfortunately) but Im guessing he is using TT med res with L/R border removal and doing a palette change in the middle of a scanline.
Im just surprised that no one has looked into this yet, as that demo was coded a good few years ago now.
...
I would not take some demo as example of usability of that 'mode' . Did you see any SW for ST(E) what draws something on Photochrome or Hi-Color display - like simple txt ? It is not impossible, but would be terribly slow and complicated.
+ TT demo is interlaced - so again, not for some serious usage, or even game. Obviously Ray found a way to do same what Photochrome does on TT - well, not really, Photochrome can more than 32 colors/line.
But all it takes 100% CPU power during screen draw. You can do something only in V-blank.

I guess that TT video stage is not configurable as Falcon's, so this is not possible with only SW .
Ahh, and demo is actually just slide show - that says everything.
I made more than it in fact, for STE - video playback at 25 fps, with res 416x228 px, 48 colors/line http://atari.8bitchip.info/movpst.php
But never thought about using overscan for some SW what needs draw on screen - not even with regular 16 colors. That's because overscan - SW overscan just loads CPU heavily - so, it is good only for some kind of slide show - and video playback is just it - only 'little' faster slide show :lol:
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Re: TT Software overscan?

Post by atari030 » Thu Jun 07, 2018 1:18 pm

There is a auto program for the STe that allows interlace in 320x200 or 640x200. I used to use is for 640x400i in 16 colours on my MegaSTe. That would have to be possible on a TT at least?

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Re: TT Software overscan?

Post by Petari » Thu Jun 07, 2018 1:34 pm

atari030 wrote:
Thu Jun 07, 2018 1:18 pm
There is a auto program for the STe that allows interlace in 320x200 or 640x200. I used to use is for 640x400i in 16 colours on my MegaSTe. That would have to be possible on a TT at least?
Certainly. Although, I would not call it 16 colors - rather headache :D And it is certainly not 640x400i - at least not on most of monitors and TVs.
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Re: TT Software overscan?

Post by mrbombermillzy » Thu Jun 07, 2018 7:35 pm

Ok. So back to just the overscan... Forget any extra colour processing, as we could just set TT low and have 256 colours so its not particularly colour starved and needing of palette switching.

I understand that it hits the 68000 quite hard on an STE, but would the 030 and faster TT bus not make it a bit more 'usable?'

Not knowing how the borders are removed on the TT makes figuring it out quite hard.

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Re: TT Software overscan?

Post by Atarian Computing » Thu Jun 07, 2018 7:58 pm

mrbombermillzy wrote:
Thu Jun 07, 2018 7:35 pm
Ok. So back to just the overscan... Forget any extra colour processing, as we could just set TT low and have 256 colours so its not particularly colour starved and needing of palette switching.

I understand that it hits the 68000 quite hard on an STE, but would the 030 and faster TT bus not make it a bit more 'usable?'

Not knowing how the borders are removed on the TT makes figuring it out quite hard.
Any good monitor will take care of the borders. My NEC 1990SXi is able to fill the screen perfectly. It can also do 1:1 pixel mapping. It displays TT-High absolutely perfectly having the same horizontal resolution of 1280 pixels. But that's all moot for me as I have a Mach64. But perhaps a gfx card is something you should consider?

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Re: TT Software overscan?

Post by Petari » Thu Jun 07, 2018 7:59 pm

On ST(E) overscan is achieved by making some writes to video registers (for freq. change) in very accurate moments of horizontal scanline. That's possible only with 100% CPU load, and knowing exact instruction execution times (cycle count) . Luckily, you can use there not only delays, but something like palette change - of course, with rigid execution time. I know only one SW, what does something else - Overscan Invaders. But that game is easy for ST, so was possible to make such code what moves objects and other, while cycle count is same. There is however one issue - it works only with keyboard. I tried to add joystick input, but that screwed timing (not because added cycles - I subtracted what it added, but because not same cycle count every time), and then graphic went corrupted. Could not solve it in simple way, so abandoned.

On TT must be same principle - and that means that CPU speed helps not - timing is what is problem. And you can not use some other way, because it will be not cycle accurate. Some will say: use Timer-B - but that's not good enough, because interrupt of it will not happen cycle accurate - it depends from what instruction executes in moment of interrupt. No wonder that it works only as slide show on TT too.
Just get some VME graphic card :lol:
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Re: TT Software overscan?

Post by mrbombermillzy » Thu Jun 07, 2018 8:30 pm

Thankyou for the definitive answer Petari! :dualthumbup:

So, basically its possible for demos, but games are pretty much out of the question.

@Atarian Computing: Do you mean you are adjusting the horizontal sizing on your monitor?

Thats all well, (I have an NEC 1990FXp, fairly similar to your monitor) however, its not really what I was trying to achieve. Was really after the extra pixels! :D

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Re: TT Software overscan?

Post by arf » Thu Jun 07, 2018 10:25 pm

atari030 wrote:
Thu Jun 07, 2018 1:18 pm
There is a auto program for the STe that allows interlace in 320x200 or 640x200. I used to use is for 640x400i in 16 colours on my MegaSTe. That would have to be possible on a TT at least?
Do you mind sharing the name and/or download link of the software?
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Re: TT Software overscan?

Post by IngoQ » Sun Jun 17, 2018 3:29 pm

Moved the rest of the topic to the Displays and Converters section here: viewtopic.php?f=30&t=90

I went a little too far off topic here ;)
Ingo :geek:

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