From: Shawn Hargreaves <Shawn AT talula DOT demon DOT co DOT uk>
Newsgroups: comp.os.msdos.djgpp
Subject: Re: "Remapping" Bitmaps In Allegro
Date: Tue, 7 Jan 1997 20:07:03 +0000
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Message-ID: <oEQJmfAnzq0yEwVt@talula.demon.co.uk>
References: <19970106 DOT 150910 DOT 9934 DOT 1 DOT MSnakes AT juno DOT com>
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To: djgpp AT delorie DOT com
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Matt J Reiferson writes:
>still not final, so I set out to write a function that would take the current 
>main pallete and "remap" it to all the tiles.  This way I would not
>have to keep each individual picture updated (the program would do it for
>me).  The problem is it doesn't work right, the tiles still don't display
>correctly, could anyone tell me what's wrong with the following function:
>
>            cerror += abs(desired[cur_data].r-actual[index].r);

I suspect this line is the problem. The color fields in a pallete are
unsigned chars. Subtract one from another, and if the actual value is
greater than the desired one (ie. approx 50% of the time), it will wrap
around and give the wrong result. Try casting the values first, eg:

    cerror += abs((int)desired[cur_data].r-(int)actual[index].r);

/*
 *  Shawn Hargreaves - shawn AT talula DOT demon DOT co DOT uk - http://www.talula.demon.co.uk/
 *  Ghoti: 'gh' as in 'enough', 'o' as in 'women', and 'ti' as in 'nation'.
 */