[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]

Looking at the original code, it does not appear to be the intention to
check for true matrix orthogonality, but only to check the upper 3x3
matrix. Although it still does not check the normality condition of
columns. Whether this is the intention, or an error I'm not sure. Would be
useful to see what the original intention was by looking at uses and talk
to the author if possible.

Thanks,
Andrew

On Fri, Jan 27, 2012 at 1:45 PM, Andrew Hale <trumanblending at gmail.com>wrote:

> 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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>>
>>
>>
>> --
>> - Campbell
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>
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