cairo-set-font-matrix (cr matrix)

cr -- a cairo-t context
matrix -- a cairo-matrix-t instance describing a transform to be applied to the current font

Sets the current font matrix to matrix. The font matrix gives a transformation from the design space of the font (in this space, the em-square is 1 unit by 1 unit) to user space. Normally, a simple scale is used, see the cairo-set-font-size function, but a more complex font matrix can be used to shear the font or stretch it unequally along the two axes.