Let's talk about Hi-Res truth and myths, I'm angry.

Any discussions related to the creation of new hardware or software for the ZX80 or ZX81
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sl07h1
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Let's talk about Hi-Res truth and myths, I'm angry.

Post by sl07h1 »

OK, I'm a little angry. I was eager to do some hi res experiment on my ZX81 and all I hear is that you only can do it with no memory extension or with a modified one. I understand the concept of pseudo hi-res, you can map the char map to a place in the ROM where if you're lucky you can find some chars that you can use. Then I made an experiment that comes in the book "The explorer's guide to the ZX81" where you modify the I register and you can map the character set to some address, it worked and, if I understand, you can map your own chars in some part of the memory (I think that I'm not understanding it well because of the "1K or modified RAM" stuff....)

And here I am, with my ZX81 with a standard Memopak 32K, playing "Rocket Man". No modified RAM extension, 32K. Looking at the numbers and the letters on screen, I would say that this is pseudo hi res, but, come on... the chicken in the start screen? COME ON!!!! I'm missing something!!

Besides that, I suck at the game!!

I need answers. How did they do it?

Angrily, thanks in advice.
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1024MAK
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Re: Let's talk about Hi-Res truth and myths, I'm angry.

Post by 1024MAK »

sl07h1 wrote: Fri Jun 11, 2021 2:29 am OK, I'm a little angry. I was eager to do some hi res experiment on my ZX81 and all I hear is that you only can do it with no memory extension or with a modified one.
Not entirely true. The Sinclair 16k RAM pack and most third party RAM packs need modification for ‘true hi-res’ graphics. But most <> all.
sl07h1 wrote: Fri Jun 11, 2021 2:29 am I understand the concept of pseudo hi-res, you can map the char map to a place in the ROM where if you're lucky you can find some chars that you can use. Then I made an experiment that comes in the book "The explorer's guide to the ZX81" where you modify the I register and you can map the character set to some address, it worked and, if I understand, you can map your own chars in some part of the memory (I think that I'm not understanding it well because of the "1K or modified RAM" stuff....)
Pseudo hi-res uses the existing bit patterns in the ROM to create a hi-res screen, but it is imperfect because occasionally the bit pattern you want is not available. Hence you don’t need hi-res ‘capable’ RAM. Internal expansions exist where you can switch out the BASIC ROM and switch in an alternate ROM or SRAM chip, either of which can contain custom bit patterns. This is what is meant by UDG on a ZX81.
sl07h1 wrote: Fri Jun 11, 2021 2:29 am And here I am, with my ZX81 with a standard Memopak 32K, playing "Rocket Man". No modified RAM extension, 32K. Looking at the numbers and the letters on screen, I would say that this is pseudo hi res, but, come on... the chicken in the start screen? COME ON!!!! I'm missing something!!

Besides that, I suck at the game!!

I need answers. How did they do it?

Angrily, thanks in advice.
It uses a custom display driver that results in a pseudo hi-res display. Hence will work without any modifications to your ZX81 RAM pack. If you really want to know how the game works, take a trip to this site ;-)

Have fun now :D

Mark
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mrtinb
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Re: Let's talk about Hi-Res truth and myths, I'm angry.

Post by mrtinb »

On the same home page, you can find the Celebration Demo. On this page your can download the Lightning Pseudo Hires Driver Source. With this source you can use many of the same tricks from the games. Try it out.
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Re: Let's talk about Hi-Res truth and myths, I'm angry.

Post by TS1000 Library User »

mrtinb wrote: Fri Jun 11, 2021 1:29 pm On the same home page, you can find the Celebration Demo. On this page your can download the Lightning Pseudo Hires Driver Source. With this source you can use many of the same tricks from the games. Try it out.
This Psuedo hires mode looks fantastic!
From the Celebration Demo page:

I'm interested to know how the technique works without requiring modification to the ram pack.

From the description "the program generates these effects using a new display driver that allows access to a wider range of pixel patterns than is available in conventional pseudo hi-res programs."

The screenshots show what look like hi-resolution characters, if they can be built from pre-existing pixel patterns with this technique it may not be necessary to redefine them. What are some other examples that make use of this graphics mode?
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mrtinb
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Re: Let's talk about Hi-Res truth and myths, I'm angry.

Post by mrtinb »

You need to use the Windows program to find which patterns are possible.
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Re: Let's talk about Hi-Res truth and myths, I'm angry.

Post by TS1000 Library User »

mrtinb wrote: Tue Jun 15, 2021 3:00 pm You need to use the Windows program to find which patterns are possible.
Thank you I will check out the programming toolkit, I've been reading more about the graphics driver on the site.
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Re: Let's talk about Hi-Res truth and myths, I'm angry.

Post by stefano »

beware, the zx81 video generation topic is a very complex one, the zx81 does it with a clever mixture of hardware and low level software tricks, in many cases it is not for free, either you bend the hardware, or the ROM, or you need lots of ram space.. or all of the above :)
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