Path: chuka.playstation.co.uk!news
From: "Nick Slaven" <NickS@ioproductions.co.uk>
Newsgroups: scee.yaroze.freetalk.english
Subject: Re: Arc tangent
Date: Thu, 30 Aug 2001 22:16:11 +0100
Organization: IO Productions Ltd
Lines: 116
Message-ID: <9mmahd$ijv2@www.netyaroze-europe.com>
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top banana!


"Jon Prestidge (Jon@surfed.to)" <jon@surfed.to> wrote in message
news:9mm95d$h6i12@www.netyaroze-europe.com...
> OK everyone.  There have been a couple of threads that could do with this
> routine of mine I think.  I am a mean get and don't usually give much
source
> code away, but I was starting to feel a bit too guilty on this one.  I did
> spend many hours writing this so keep it to yourselves and give me a
mention
> if you use it.  It's not too accurate however (I do have a more up-to-date
> version that I've developed that is more accurate, but it is also slower
so
> I think this is the one best suited).
>
> Just find dx and dy and pass `em to this routine and sit-back and have
this
> routine do all the work for you.  Get it while it's hot.
>
> Jon
>
>
> long auto_arc_tan( long v_dx, long v_dy )
>    {
>    // (c) Jon Prestidge 1997    Do not copy, do not distribute.
>    // Version 1.0
>    // automatic arc tangent routine.  Just plug-in dx and dy and
>    // get back a full angle between 0 and 4096.
>    //
>    long grad, ang, abs_dx, abs_dy, half;
>
>    abs_dx = v_dx;
>    if ( abs_dx < 0 ) abs_dx *= -1;
>    abs_dy = v_dy;
>    if ( abs_dy < 0 ) abs_dy *= -1;
>
>    // find the gradient between 0 and one (or 0 and 4096 in this
> impelmentation)....
>    if ( abs_dy <= abs_dx )
>       {
>       if ( abs_dx == 0 )
>          { // exact angle can be returned... also this prevents divide by
0
> error...
>          if ( v_dy >= 0 )
>             return 0;
>          else
>             return 2048;
>          }
>       grad = abs_dy;
>       grad <<= 12;
>       grad /= abs_dx;
>       half = 1;
>       }
>    else
>       {
>       if ( abs_dy == 0 )
>          { // exact angle can be returned... also this prevents divide by
0
> error...
>          if ( v_dx >= 0 )
>             return 1024;
>          else
>             return 3072;
>          }
>       grad = abs_dx;
>       grad <<= 12;
>       grad /= abs_dy;
>       half = 0;
>       }
>
>    ang = ( grad * 2409 ) >> 12;
>    ang *= 4096 - ang;
>    ang += grad * 3097;
>    ang >>= 15;
>
>    if ( v_dx >= 0 )
>       {
>       if ( v_dy >= 0 )
>          {
>          if ( half ) ang = 1024 - ang;
>          }
>       else
>          {
>          if ( half )
>             ang += 1024;
>          else
>             ang = 2048 - ang;
>          }
>       }
>    else
>       {
>       if ( v_dy >= 0 )
>          {
>          if ( half )
>             ang += 3072;
>          else
>             ang = 4096 - ang;
>          }
>       else
>          {
>          if ( half )
>             ang = 3072 - ang;
>          else
>             ang += 2048;
>          }
>       }
>
>    return ang;
>    }
>
>
>