Path: chuka.playstation.co.uk!scea!peter_alau@playstation.sony.com
From: "Michael Hough" <mhough@stanford.edu>
Newsgroups: scea.yaroze.programming.3d_graphics
Subject: Re: Quaternion 2 Matrix ...
Date: Sun, 23 May 1999 13:37:32 -0700
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Markus Tesche <m.tesche@blup.de> wrote in message
news:7i9jkp$lic17@chuka.playstation.co.uk...
> M->m[0][0] = (ONEsqr - (yy + zz)) / ONE;
> M->m[0][1] = (xy + wz) / ONE;
> M->m[0][2] = (xz - wy) / ONE;
>
> M->m[1][0] = (xy - wz) / ONE;
> M->m[1][1] = (ONEsqr - (xx + zz)) / ONE;
> M->m[1][2] = (yz + wx) / ONE;
>
> M->m[2][0] = (xz + wy) / ONE;
> M->m[2][1] = (yz - wx) / ONE;
> M->m[2][2] = (ONEsqr - (xx + yy)) / ONE;
>
> M->t[0] = 0;
> M->t[1] = 0;
> M->t[2] = 0;
> }
>
> OK, thanks, Bye MT

    I was having a similar problem.  I ran through the math a while ago, and
it looks like you need to flip the signs on your (xy + wz) etc. terms:

  m->m[0][0] = 4096 - (yy + zz);
  m->m[0][1] = xy - wz;
  m->m[0][2] = xz + wy;

  m->m[1][0] = xy + wz;
  m->m[1][1] = 4096 - (xx + zz);
  m->m[1][2] = yz - wx;

  m->m[2][0] = xz - wy;
  m->m[2][1] = yz + wx;
  m->m[2][2] = 4096 - (xx + yy);

This seems to be working for me.

mike