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From: sdh@thumper.UUCP
Newsgroups: comp.sys.apple
Subject: On hi-res character generation
Message-ID: <394@thumper.UUCP>
Date: Fri, 13-Feb-87 11:14:04 EST
Article-I.D.: thumper.394
Posted: Fri Feb 13 11:14:04 1987
Date-Received: Thu, 19-Feb-87 07:14:29 EST
Distribution: net
Organization: Bell Communications Research Inc., Morristown, NJ
Lines: 32


Just a simple point, that it is fact very easy to do scrolling
for a hires character generator that is just as fast as normal
test scrolling.  The way to do this is to write a program that
builds a scroll routine.  The end result is a program that
would look something like this:

	LDY #$00
label   LDA ${the address of the 8th line of video},Y
	STA $2000,Y {the first line of video}
	LDA ${the 9th line},Y
	STA $2400,Y
	.
	.
	.
	INY
	CPY #$28
	BNE label1
	RTS
label1  JMP label

This just does huge amounts of raw moving, and will scroll the screen
tremendously fast (compared with the normal way of scrolling.

This does not allow windowing, though.  That can be added into code of
this sort, but it slows it down.

Also, this technique extended to the text screen gives phenomenal
scrolling there too.  You never new the screen could go by so fast.

Retief of the CDT
(ucbvax, decvax, ihnp4)!bellcore!sdh