dx,dy) by matrix. This is
similar to cairoMatrixTransformPoint except that the translation
components of the transformation are ignored. The calculation of
the returned vector is as follows:cairoMatrixTransformDistance(matrix, dx, dy)x1,y1) transforms
to (x2,y2) then (x1+dx1,y1+dy1) will transform to
(x1+dx2,y1+dy2) for all values of x1 and x2.