There is disclosed a non-transitory machine readable storage medium encoded with instructions executable by a processor and comprising instructions to: receive object data corresponding to a three-dimensional object to be generated; define print data for each of a plurality of slices of the object to control a respective layer forming operation in which print agent is ejected on a layer of build material in a pattern corresponding to selective fusing of the build material, wherein the print data and the respective pattern is defined for each slice according to object a print definition procedure; and select the print definition procedure from a plurality of print definition procedures based on a user input. There is also disclosed a corresponding method and additive manufacturing apparatus.