New ZX81 Game: Against The Elements

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kokkiklhs
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Re: New ZX81 Game: Against The Elements

Post by kokkiklhs »

Superb!! Thank you Paul! I just tested it on my TS100!!
If only Sir Clive could see this, back in 1981... :D
Steven McDonald_81
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Re: New ZX81 Game: Against The Elements

Post by Steven McDonald_81 »

An amazing achievement.
How I poured over knight lore and wondered if it was ever possible on the zx81. A dream come true!
I abandoned my idea back in the day as I concluded it absolutely impossible with the constraints of pseudo hires..

How wrong!

Amazing piece of software and a great game!

Can I ask a few technical details regarding the initial title page.

What value of the I register was used to generate the character sets shown?

The font for the lower case especially looks flawless - can you share some details on it thanks.
Fruitcake
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Joined: Wed Sep 01, 2010 10:53 pm

Re: New ZX81 Game: Against The Elements

Post by Fruitcake »

Thanks to all for your kind comments about the game. It makes all the effort worthwhile.
Steven McDonald_81 wrote:The font for the lower case especially looks flawless - can you share some details on it thanks.
The game actually uses multiple pseudo hi-res techniques. The title screen is generated using the technique first devised (as far as I know) by Software Farm in the game Z-Xtricator. The technique differs in that it does not reset the hardware line counter after every scan line. This means that each of the 8 lines access a different set of pixel patterns in the ROM. Z-Xtricator and my title screen both access the standard ROM character set pixel patterns. By setting all line codes for a cell to the same value, the 8 pixel patterns for a standard ROM character are fetched and so the cell displays a normal character. But it is now possible to set each line code to point to the pixel pattern from another character. Lower case and upper case lettering have fairly similar characteristics and so the patterns that make up the upper case letters are well suited for constructing lower case letters. This is how I have been able to mix standard upper case letters with lower case letters on the same row.

Z-Xtricator did not use the technique to display lower case letters but instead used it to create some very neatly formed aliens, which was possible because the pixel patterns in the ROM character set generally form short continuous lines or have a symmetrical looking arrangement to them. This is why the sprites in the game don't have any of the misshapen appearance of those in Forty Niner, Rocketman and
Booster.

However the technique comes with the limitation that it is not possible to scroll the display vertically at a pixel resolution. Scrolling can only happen at the character resolution, but horizontal scrolling is already subject to a similar limitation and so for many games this would be perfectly adequate and would be a good trade off for neater graphics. I always felt it was ideal for this purpose but I'm not aware of other programs that use it (if anyone knows of any then I would be interested to hear about them).

Using the technique it is possible to construct (with reasonably high quality) every lower case letter:
HiResCharSet.gif
HiResCharSet.gif (509 Bytes) Viewed 13330 times
And the standard block graphic symbols can also be created, along with punctuation symbols, underlined characters, etc.
Last edited by Fruitcake on Thu Mar 17, 2016 10:31 pm, edited 1 time in total.
nollkolltroll
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Location: Stockholm, Sweden

Re: New ZX81 Game: Against The Elements

Post by nollkolltroll »

A very good explanation of the lower-case technique, thanks.
/Adam
Fruitcake
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Re: New ZX81 Game: Against The Elements

Post by Fruitcake »

I've made the bitmap definitions for the lower case letters, along with other symbols necessary for a full ASCII character set, available for download from my website on the page for the program Celebration.
sirmorris
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Re: New ZX81 Game: Against The Elements

Post by sirmorris »

(Like)
nollkolltroll
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Re: New ZX81 Game: Against The Elements

Post by nollkolltroll »

Another BIG like!
/Adam
solaris104
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Re: New ZX81 Game: Against The Elements

Post by solaris104 »

This is fantastic game. I have finished the game :) .
sirmorris
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Joined: Thu May 08, 2008 5:45 pm

Re: New ZX81 Game: Against The Elements

Post by sirmorris »

... wow!
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