the name of a file to write to
CAIRO_STATUS_SUCCESS if the PNG file was written successfully. Otherwise, CAIRO_STATUS_NO_MEMORY if memory could not be allocated for the operation or CAIRO_STATUS_SURFACE_TYPE_MISMATCH if the surface does not have pixel contents, or CAIRO_STATUS_WRITE_ERROR if an I/O error occurs while attempting to write the file.
Writes the contents of surface to a new file filename as a PNG image. Since 1.0