pango:matrix-transform-distance (matrix dx dy)

matrix -- a pango:matrix instance
dx -- a number coerced to a double float for the x component
dy -- a number coerced to a double float for the y component

The double floats for the transformed distance vector (dx,dy).

Transforms the distance vector (dx,dy) by matrix. This is similar to the pango:matrix-transform-point function except that the translation components of the transformation are ignored. The calculation of the returned vector is as follows:

dx2 = dx1 * xx + dy1 * xy;
dy2 = dx1 * yx + dy1 * yy;  

Affine transformations are position invariant, so the same vector always transforms to the same vector. If (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.