From:	Flenser <flenser AT cs DOT iastate DOT edu>
Newsgroups:	comp.os.msdos.djgpp
Subject:	Re: ANDing bitmaps under allegro
Date:	Fri, 05 Nov 1999 14:41:26 -0600
Organization:	Iowa State University, Ames, Iowa, USA
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To:	djgpp AT delorie DOT com
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Yes, that's what I had in mind. Thanks again.

gradha AT iname DOT com wrote:

> Flenser <flenser AT cs DOT iastate DOT edu> wrote:
> > The operation was called and under Paint Shop's arithmetic operations dialog, that's all
> > I know about it. Your idea works fine, I was just hoping that there was some magic
> > solution that didn't involve going through each pixel and testing it. Thank you for your
> > help.
>
> Well, I think there is (partially). You can reduce the ifs if you
> _really_ AND the image. For this, let's say that color 255 is the
> one which will show the image, color 0 is the one which will block
> the image.
>
> With this assumption, you first clear your final bitmap to black or
> white, and then something like:
>
> for (y=0;y<bmp_final->h;y++)
>         for (x=0;x<bmp_final->h;x++)
>                 putpixel(bmp_final,x,y,
>                         getpixel(bmp_source,x,y) & getpixel(bmp_mask,x,y);
>
> Since 255 is 1111 1111 in bits, your source image will be shown.
> Color 0, which is 0000 0000 in bits, will put color 0 on your
> destination bitmap.
>
> Ok, so this really is ANDING, which you requested in first place.
> Sorry for the "way-round" I initially took :-)
>
> The problem was that I was thinking about an algorithm which you
> could feed any image, greyscale it, make it black&white, etc.
>
> Grzegorz Adam Hankiewicz - gradha AT iname DOT com
> Gogosoftware - http://welcome.to/gogosoftware/
>
> "She broke my heart. I broke her neck. Now we are even, aren't we?"

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