Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Path: utzoo!utgpu!water!watnot!watmath!clyde!rutgers!dayton!mmm!srcsip!cimbura
From: cimbura@srcsip.UUCP
Newsgroups: comp.sys.apple
Subject: Re: On hi-res character generation
Message-ID: <238@srcsip.UUCP>
Date: Fri, 6-Mar-87 15:26:44 EST
Article-I.D.: srcsip.238
Posted: Fri Mar  6 15:26:44 1987
Date-Received: Sun, 8-Mar-87 16:17:47 EST
References: <836@pbhyd.UUCP>
Organization: Honeywell S&RC Inc., MPLS, MN
Lines: 44

in article <836@pbhyd.UUCP>, lc@pbhyd.UUCP (Larry Colton) says:
> 
> In article <394@thumper.UUCP> sdh@thumper.UUCP (Retief of the CDT) writes:
>>
>>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.  
> 
> I presume the author of the above meant to say hi-res screens
> could be made to scroll as fast as *text* screens.  Not hardly.
> Each line of text on a text screen requires one line of screen
> memory (40 bytes).  Each 'text' line on a hi-res screen requires 8 
> lines of screen memory (320 bytes).  Since a memory move routine does
> not care what memory is being moved, it should be obvious that the
> best a hi-res scroll can do is 8 times slower than text scroll.
> 
> Some other factors will impact this (80 column text, use of look
> up tables instead of bascalc, etc) but in no case will hi-res 
> scrolling ever be as fast as text screen scrolling.

It may not ever be as fast as normal text scrolling but it can approach
great speed through the method indicated (building a scroll routine.)
The trade off is program memory space for speed.  The routine would
do direct memory moving which is much faster than any calculations or even
using look up tables can approach.  Although this is not really practical
for an entire screen it may be done on a small portion of the screen
easily if speed is really a problem.
A program segment might look something like this...
       ldx #0
loop:  lda $2000,x
       sta $2010,x
      ... (many more loads and stores)...
       inx
       cpx #40
       bcc loop
Well anyways.  See ya.

-- 
Tim Cimbura       {ihnp4,philabs,umn-cs,mmm}!srcsip!cimbura
Honeywell S&RC, Signal and Image Processing       MN65-2300
Artificial Intelligence Technology
3660 Technology Drive
Minneapolis, MN  55413                       (612) 782-7537