Author Topic: How to scroll / shift screen content??  (Read 354 times)

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Offline HAL 6128

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How to scroll / shift screen content??
« on: 23:00, 04 May 20 »
Just a short question: is there a possibility to scroll or shift the screen content without changing the screen base address as it is with a hardware scroll?

For example in BASIC modus: if I scroll with help of the cursor the screen at the end one line down or up and do "LOCATE 1,1:PRINT "TEST"" then the message is done in the correct position. If I do a hardware scroll (like it is done here: http://cpctech.cpc-live.com/source/hardscrl.html) then the message and everything else is also shifted.
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Offline roudoudou

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Re: How to scroll / shift screen content??
« Reply #1 on: 23:04, 04 May 20 »
if you do not change the screen base adress it's obviously moving data with CPU (most of games are redrawing the entire screen)
use RASM, the best assembler ever made :p

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Offline HAL 6128

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Re: How to scroll / shift screen content??
« Reply #2 on: 23:19, 04 May 20 »
What happens then if the firmware scrolls one line up or down (e.g. with the firmware call &BC4D)? It doesn't seem to change the base address or is it calculating afterwards? The area scrolled outside seems to be deleted and doesn't appear on the other side again.
« Last Edit: 23:22, 04 May 20 by HAL 6128 »
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Offline andycadley

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Re: How to scroll / shift screen content??
« Reply #3 on: 23:31, 04 May 20 »
The firmware changes the base address. It just also does the work to clear the scrolled in area.

Offline IndyUK

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Re: How to scroll / shift screen content??
« Reply #4 on: 14:48, 16 June 20 »
The firmware changes the base address. It just also does the work to clear the scrolled in area.
Hi

Sorry to be cheeky and piggy back on this thread but, can you please explain exactly what this firmware call scrolls? Having read about this in the firmware guide, I can't see which part of the memory is being targetted. I put some test code together a few weeks ago (must go back to it) and remember thinking to myself at that time, how does one use this?

Thanks