cairo:matrix (cr matrix)

cr -- a cairo:context-t instance
matrix -- a cairo:matrix-t transformation matrix from user space to device space

The cairo:matrix function gets the current transformation matrix (CTM). The (setf cairo:matrix) function modifies the current transformation matrix (CTM) by setting it equal to matrix. The cairo:matrix-t structure is a foreign CFFI structure, therefore we pass in a valid cairo:matrix-t instance to the cairo:matrix function which is filled with the current transformation matrix.