[Bf-committers] [Bf-blender-cvs] SVN commit: /data/svn/bf-blender [43733] trunk/blender/source/blender/ blenlib/intern/math_matrix.c: Fix orthogonality check for mat3 and mat4

[Andrew Hale]

Hi Campbell,

This fix adds the condition that the columns be unit length which is a
requirement of orthogonal matrices [1].

>From Python you can check this with the code here [2]. This matrix is not
orthogonal, even though its columns are. For another example of a matrix
which has orthogonal columns but the matrix is not orthogonal, see here [3].

If the intention of the function is to check for true matrix orthogonality
then this change is consistent.

Cheers,
Andrew

PS That 1 in the final "if" should be 1.0f shouldn't it?

[1] http://mathworld.wolfram.com/OrthogonalMatrix.html
[2] http://www.pasteall.org/28577/python
[3] http://en.wikipedia.org/wiki/Orthogonal_matrix#Properties

On Fri, Jan 27, 2012 at 4:23 AM, Campbell Barton <ideasman42 at gmail.com>wrote:

> Can you give an example as to what case this fixes?
>
> On Fri, Jan 27, 2012 at 4:11 AM, Sv. Lockal <lockalsash at gmail.com> wrote:
> > Revision: 43733
> >
> http://projects.blender.org/scm/viewvc.php?view=rev&root=bf-blender&revision=43733
> > Author:   lockal
> > Date:     2012-01-26 17:11:43 +0000 (Thu, 26 Jan 2012)
> > Log Message:
> > -----------
> > Fix orthogonality check for mat3 and mat4
> >
> > Modified Paths:
> > --------------
> >    trunk/blender/source/blender/blenlib/intern/math_matrix.c
> >
> > Modified: trunk/blender/source/blender/blenlib/intern/math_matrix.c
> > ===================================================================
> > --- trunk/blender/source/blender/blenlib/intern/math_matrix.c   2012-01-26
> 17:03:30 UTC (rev 43732)
> > +++ trunk/blender/source/blender/blenlib/intern/math_matrix.c   2012-01-26
> 17:11:43 UTC (rev 43733)
> > @@ -778,32 +778,38 @@
> >        mul_v3_fl(mat[2], size[2]);
> >  }
> >
> > -int is_orthogonal_m3(float mat[][3])
> > +int is_orthogonal_m3(float m[][3])
> >  {
> > -       if (fabsf(dot_v3v3(mat[0], mat[1])) > 1.5f * FLT_EPSILON)
> > -               return 0;
> > +    int i, j;
> >
> > -       if (fabsf(dot_v3v3(mat[1], mat[2])) > 1.5f * FLT_EPSILON)
> > -               return 0;
> > +    for (i = 0; i < 3; i++) {
> > +        for (j = 0; j < i; j++) {
> > +            if (fabsf(dot_v3v3(m[i], m[j])) > 1.5f * FLT_EPSILON)
> > +                return 0;
> > +        }
> >
> > -       if (fabsf(dot_v3v3(mat[0], mat[2])) > 1.5f * FLT_EPSILON)
> > -               return 0;
> > -
> > -       return 1;
> > +        if (fabsf(dot_v3v3(m[i], m[i]) - 1) > 1.5f * FLT_EPSILON)
> > +            return 0;
> > +    }
> > +
> > +    return 1;
> >  }
> >
> > -int is_orthogonal_m4(float mat[][4])
> > +int is_orthogonal_m4(float m[][4])
> >  {
> > -       if (fabsf(dot_v3v3(mat[0], mat[1])) > 1.5f * FLT_EPSILON)
> > -               return 0;
> > +    int i, j;
> >
> > -       if (fabsf(dot_v3v3(mat[1], mat[2])) > 1.5f * FLT_EPSILON)
> > -               return 0;
> > +    for (i = 0; i < 4; i++) {
> > +        for (j = 0; j < i; j++) {
> > +            if (fabsf(dot_vn_vn(m[i], m[j], 4)) > 1.5f * FLT_EPSILON)
> > +                return 0;
> > +        }
> >
> > -       if (fabsf(dot_v3v3(mat[0], mat[2])) > 1.5f * FLT_EPSILON)
> > -               return 0;
> > -
> > -       return 1;
> > +        if (fabsf(dot_vn_vn(m[i], m[i], 4) - 1) > 1.5f * FLT_EPSILON)
> > +            return 0;
> > +    }
> > +
> > +    return 1;
> >  }
> >
> >  void normalize_m3(float mat[][3])
> >
> > _______________________________________________
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> > Bf-blender-cvs at blender.org
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>
>
>
> --
> - Campbell
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