Computes the affine transform of the vpath, using matrix as the
transform. matrix is stored in the same format as PostScript, ie.
x' = matrix[0] * x + matrix[2] * y + matrix[4]
y' = matrix[1] * x + matrix[3] * y + matrix[5]

src :

Source vpath to transform.

matrix :

Affine transform.

Returns :

the newly allocated vpath resulting from the transform.