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From: eli@aspasia.gang.umass.edu (Eli Brandt)
Newsgroups: comp.lang.pascal
Subject: Re: Graphic-screen to disk
Message-ID: <22706@dime.cs.umass.edu>
Date: 16 Nov 90 17:53:39 GMT
References: <25017@adm.brl.mil>
Sender: news@dime.cs.umass.edu
Reply-To: eli@aspasia.CS.UMASS.EDU (Eli Brandt)
Organization: University of Massachusetts, Amherst
Lines: 38

In article <25017@adm.brl.mil> S89405079%HSEPM1.HSE.NL@uga.cc.uga.edu writes:
>Hi,
>
>I have a little problem dumping the graphics-screen to disk. The problem is
>that when I dump such a screen, all the colors disappear. Does anyone
>know what I'm doing wrong?
>
>Edwin Groothuis
>S89405079@hsepm1.hse.nl
>
>============================ PROGRAM ==========================
>uses       crt,dos,graph;
>type       screen_type:array[0..$FFFF] of byte;
>var        fil:file of screen_type;
>           screen:^screen_type;
>           driver,mode:integer;
>           i:integer;
>
>begin
>  detectgraph(driver,mode);
>  initgraph(driver,mode,'');
>  for i:=1 to 100 do
>    circle(100,100,i);                (* Make something on the screen *)
>  screen:=ptr($A000,0000)
>  assign(fil,'test');rewrite(fil);write(fil,screen);close(fil);
>  clearviewport;
>  assign(fil,'test');reset(fil);read(fil,screen);close(fil);
>end.

Well, if you're getting anything, you're presumably in EGA/VGA mode.  These
modes store the frame buffer as 4 bitplanes, all mapped to the A000 segment.
What you get when you read/write depends on the status of the select and
mask registers.  The simplest way to get a screen dump would probably be to
pull each of the four bitplanes in turn, and put them back the same way.
If you don't have a reference for the registers, e-mail me and I'l get back to
you after I've looked it up. :-)

Eli