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The current transforms and 3D transforms specification lack a code example or algorithm how to unmatrix 3d transforms.
Actually the 3D transform specification points to a code demo that isn't available anymore. It is still possible to find this document in google cache: http://webcache.googleusercontent.com/search?q=cache:I3WG5UP6WsgJ:tog.acm.org/resources/GraphicsGems/gemsii/unmatrix.c+http://tog.acm.org/GraphicsGems/gemsii/unmatrix.c I would still suggest adding an algorithm in a separate section in the specification text directly.
The old editor's draft of FX 2D Transforms 1.0, Part 2 provides a quite clean code for decomposing 4x4 matrices. I also suggests to transform a 3x2 2D matrix into a 4x4 matrix and use the same algorithm: http://dev.w3.org/Graphics-FX/modules/2D-transforms/spec/2DTransforms.html#sec-transform-lists-nested-transformations I suggest adapting the section "Matrix decomposition for animation" into CSS Transforms. It just needs to specify that matrix[x][y] is a two dimensional array and if x represents the column or row.
I back ported the 3D pseudo code from FX Transforms and replaced the (partly) wrong 2D code with it. Any dissenting votes? Can we close this bug?