Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!uunet!timbuk!shamash!mpe
From: mpe@shamash.cdc.com (Mike Ebsen)
Newsgroups: comp.lang.pascal
Subject: Re: Storing screen image for quick display
Message-ID: <30020@shamash.cdc.com>
Date: 23 Jan 91 14:39:47 GMT
References: <8416@hub.ucsb.edu>
Distribution: comp
Organization: Control Data, Arden Hills, MN
Lines: 15

If you read many of the svga ads you'll see references to either 256K, 512K
or even a 1meg vga board.  This is the amount of "RAW" storage which the
CRT display controller has to maintain the images that we see.  Using 
rather simple mathematics you can compute the actual requirements:
     Total := getmaxx * getmaxy * bytes_per_pixel;
           := 640     * 480     * 1 (usually)
           := 307200 (a bit more than the 64K max data segment allows!)

You could create 10 (or so) smaller array structures, each approx 30K but
this is messy and comsumes all of the available heap and static memory.  The
best approach that I can think of is to use the paging structure built into 
every graphics display card.  By  setting SetActivePage and SetDisplayPage
correctly, you can manage two seperate display maps, completely within the
hardware and memory you already have and not be troubled by large messy 
data structers.