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From: zech@leadsv.UUCP (Bill Zech)
Newsgroups: comp.lang.pascal
Subject: Re: 256 colour mode in TP5.0
Summary: VGA registers are readable
Message-ID: <10334@leadsv.UUCP>
Date: 14 Mar 90 06:42:26 GMT
References: <25F744E5.8753@maccs.dcss.mcmaster.ca> <18812@shamash.cdc.com>
Organization: LOCKHEED, Sunnyvale, CA
Lines: 19

In article <18812@shamash.cdc.com>, mpe@shamash.cdc.com (2375) writes:
> The problem of capturing images using turbo pascal is that there is no way
> to read the palette registers back from the display controller card.  Within
> the run-time environment, an array of previous values is used by the BGI 
> graphics manager to shadow the palette contents.  Long before you invoke your
> getimage program, a TSR that captures the int 10 interupt commands which update
>  the CRT control, must monitor all int 10's for potential palette updates.
> Also, each shell opened by the user, loads it's own version of the command.com
> and *.bgi file base and therefore creates a yet another set of palette array
> registers.  Good luck.

This is not true for a VGA card.  All the registers (save one minor one,
I believe) are both readable and writable.  The EGA and CGA boards 
were write-only, but the VGA fixes that problem.  

Also, I believe there is a procedure in the graphics.tpu to read
the pallete registers.

- Bill