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When converting from Matrix44 to Matrix33, the third row and column is dropped.
` [ a b _ c ] [ a b c ] [ d e _ f ] -> [ d e f ] [ _ _ _ _ ] [ g h i ] [ g h _ i ] `*
When converting from Matrix44 to Matrix33, the third row and column is dropped.
` [ a b _ c ] [ a b c ] [ d e _ f ] -> [ d e f ] [ _ _ _ _ ] [ g h i ] [ g h _ i ] `*