[ggt-devel] [ ggt-Bugs-3593340 ] invert (c, transpose (b, a))

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Bugs item #3593340, was opened at 2012-12-06 13:54
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Category: GMTL
Group: 0.1.x
Status: Open
Resolution: None
Priority: 5
Private: No
Submitted By: https://www.google.com/accounts ()
Assigned to: Nobody/Anonymous (nobody)
Summary: invert (c, transpose (b, a))

Initial Comment:
Given an AFFINE Matrix44f with translation components in column [3], this sequence gives an incorrect result:

   Matrix44f a, b, c;
   // Set matrix a with non-zero translation and a.mState = AFFINE
   invert (c, transpose (b, a));

The problem is that transpose merely copies the mState (AFFINE), so invert calls invertAffine, which contains this:

      // handle matrices with translation
      if (COLS == 4)
      {
         // The right column vector of the matrix should always be [ 0 0 0 s ]
         // this represents some shear values
         result[3][0] = result[3][1] = result[3][2] = 0;

There are two work-arounds:

*  Reverse the order of operations (which is mathematically equivalent and avoids the bug):

      // invert (c, transpose (b, a));  // transpose fails to change mState, invert makes bad assumption
      transpose (c, invert (b, a));  // avoid the bug

*  Force mState to FULL before invert:

      transpose (b, a);
      b.mState = FULL;
      invert (c, b);




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