From: hellbaron <hellknightNOheSPAM AT hotbot DOT com DOT invalid>
Subject: Help with graphix negative image fractal function
Newsgroups: comp.os.msdos.djgpp
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Date: Thu, 30 Dec 1999 22:33:49 -0800
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To: djgpp AT delorie DOT com
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Reply-To: djgpp AT delorie DOT com

I am in the process of learning how to use c properly, and i am working
on a fractal project but i am having trouble developing a function that
displays a negative rectangle over a specified area. I am working on a
640x480x8bit graphic environment for the fractal, and the idea was to
create a negative rectangle over the fractal that could then be erased
simply by placing another one over it.. I hope you understand the
concept, its quite simple actualy, well anywayz, here is the function,
I await impaciently for your helpful feedback, thanx in advance to
anyone who reads this...

void xrectf(int x1, int y1, int x2, int y2)
{
        int x, y, px, py, c1, swap;
        int xrectf[ABS(x2-x1)][ABS(y2-y1)];

        if (x1>x2) {swap=x1;x1=x2;x2=swap;}
        if (y1>y2) {swap=y1;y1=y2;y2=swap;}

        for (x=x1, px=0; x<(x2+1); x++, px++)
                for (y=y1, py=0; y<(y2+1); y++, py++)
                        xrectf[px][py]=getpixel(x, y);

        for (x=x1, px=0; x<(x2+1); x++, px++)
                for (y=y1, py=0; y<(y2+1); y++, py++)
                {
                        c1=xrectf[px][py]+128;
                        if (c1 > 255 ) c1 -= 256;
                        putpixel(x, y, c1);
                }
}




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