[Openexr-devel] extractScaling from matrices doesn't work with negative scales?

[Benoit Leveau]

Hi,

I'm probably doing something wrong, but it looks like if you have a negative 
scaling in your matrix the extractScaling function (and other functions like 
removeScaling that use it)
doesn't work properly.

I just tried the following very simple example, and got the same incorrect 
result using OpenEXR 1.4 or 1.7.

Thanks for your help,
Benoit

----------------

#include <OpenEXR/ImathMatrixAlgo.h>
#include <iostream>
int main(int argc, char **argv)
{
        Imath::M44f m;
        Imath::V3f vec;
        for (int i=0;i<4;++i)
                for (int j=0;j<4;++j)
                {
                        m.x[i][j] = 0;
                }
        m.x[3][3] = 1;

        m.x[0][0] = 1;  m.x[1][1] = 2;  m.x[2][2] = 3;
        std::cout <<"matrix = " << std::endl << m << std::endl;
        if (extractScaling(m,vec,true))
                std::cout <<"extracted scaling:" <<std::endl << vec << 
std::endl;

        m.x[0][0] = -1; m.x[1][1] = 2;  m.x[2][2] = 3;
        std::cout <<"matrix = " << std::endl << m << std::endl;
        if (extractScaling(m,vec,true))
                std::cout <<"extracted scaling:" <<std::endl << vec << 
std::endl;

        return 0;
}

----------------
Output:
-------

matrix = 
(  1.000000e+00   0.000000e+00   0.000000e+00   0.000000e+00
  0.000000e+00   2.000000e+00   0.000000e+00   0.000000e+00
  0.000000e+00   0.000000e+00   3.000000e+00   0.000000e+00
  0.000000e+00   0.000000e+00   0.000000e+00   1.000000e+00)

extracted scaling:
(1 2 3)
matrix = 
( -1.000000e+00   0.000000e+00   0.000000e+00   0.000000e+00
  0.000000e+00   2.000000e+00   0.000000e+00   0.000000e+00
  0.000000e+00   0.000000e+00   3.000000e+00   0.000000e+00
  0.000000e+00   0.000000e+00   0.000000e+00   1.000000e+00)

extracted scaling:
(-1 -2 -3)