Moving the margins on the screen

Any discussions related to the creation of new hardware or software for the ZX80 or ZX81
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Shaun_B
Posts: 474
Joined: Wed Apr 22, 2009 10:22 am

Moving the margins on the screen

Post by Shaun_B »

I've noticed that it's fairly easy to generate 33 or 34 column text on the ZX81, so let's say I want 34 x 24 text display, is it possible to move the screen position left one character to compensate?

Also, if I wanted, say, 30 X 25 text (if that's possible), could I move the screen right and up easily enough?

Are there any assembly tricks to do such wizardry?

Thanks,

Shaun.
dr beep
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Joined: Thu Jun 16, 2011 8:35 am
Location: Boxmeer

Re: Moving the margins on the screen

Post by dr beep »

Count the columns in my game AIRPIPES and you have the answer.
You can move the text by a column when you alter the value in A just before calling the print from the ROM.

Since the ZX81 can handle less than 32 bytes (compressed screen) it can also handle more by just making a screen wirh more columns.
As for more textlines than 24: just increase the B-register.

However: the ROM will reset the screen to 32x24 when you use CLS, so this must be avoided ( make your own CLS).
The best way to use this all is in MC, so do not return to BASIC anymore.
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siggi
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Location: Wetterau, Germany
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Re: Moving the margins on the screen

Post by siggi »

My ZX81 web-server: online since 2007, running since dec. 2020 using ZeddyNet hardware
http://zx81.ddns.net/ZxTeaM
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