position-transform

Arguments: position matrix

Transforms the given position with the supplied matrix, which is a 2 by 2 array (or larger 2-dimensional array -- extra cells of the array are ignored). Even if the elements of matrix are floats, the returned position will have rounded whole number components. The transform works as follows:

xnew = A(0,0)*xold + A(0,1)*yold
ynew = A(1,0)*xold + A(1,1)*yold

For example:

 (setq ar (make-array '(2 2) 
            :initial-contents '((5.0 2.0) (3.0 1.0))))
 (setq p1 (make-position 7 10))
 (position-transform p1 ar)
returns
#.(make-position 55 31) ; = 5*7 + 2*10, 3*7 + 1*10

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Created 2010.1.21.