cairo_surface_t *
cairo_image_surface_create (cairo_format_t      format,
                            int                 width,
                            int                 height);

cairo_surface_t *
cairo_image_surface_create_for_data (unsigned char             *data,
                                     cairo_format_t             format,
                                     int                        width,
                                     int                        height,
                                     int                        stride);

The fact that one arg is added before and one after is just really
peculiar. I'd strongly suggest that both args should be added after,
which also fits in the "optional argument" idea.