[zxspectrum] Re: errore 404 ;)

  • From: Mario Prato <mario.prato@xxxxxxxx>
  • To: zxspectrum@xxxxxxxxxxxxx
  • Date: Tue, 20 Jul 2004 13:59:45 +0200

Cioè vuoi dire che lo ZX81 ha già l'hardware necessario per lavorare in alta risoluzione? Non lo sapevo!

a quanto pare no, hai bisogno di qualche add-on, dalle faq dello ZX81:

Q: Could you get hi-res graphics on a ZX81?

A: Yes. There were a number of ways.

1. The Z80's i register pointed to a font table. You could move this around in the ROM to create swirly graphics effects. The game Astral Convoy did this. Unfortunately, the design of the ZX81 made it impossible for the character set to be anywhere in the 16K range, so you couldn't have a user defined set without extra hardware. With a 64K RAM pack you could disable the ROM shadow between 8K and 16K and design your own UDGs.

2. CRL released a Hi-Res graphics toolkit. This contained an extremely hairy interrupt routine that replaced the ZX81's usual display update routine. Basically, it pointed the i register to a strategic ROM location, and tried to 'best fit' the HRG display to what it could find in those locations. It also used a feature of the ZX81's hardware that allowed you to have 1 pixel height characters to improve it's chances.

You still could, at best, only have 128 different combinations out of the 256 possible ones. These were the 64 'characters' and their inverses. So this is really pseudo-HRG.

A number of games by Software Farm, including Hi-Res Invaders and Rocket Man, used this technique.

With a 64K RAM pack you could also, alter the font, allowing an even better chance of getting the characters you need. Some people made an alteration to their ZX81's internal wiring, so that the i register can point to the 16K RAM area, allowing them to do the same.

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