1. A method comprising: identifying a primitive to be processed for a tile of a graphics output being processed; determining whether already-calculated primitive-specific data for the primitive is stored in a memory; and when it is determined that already-calculated primitive-specific data for the primitive is stored in the memory, retrieving stored primitive-specific data for the primitive and using that stored data to process the primitive; when it is determined that already-calculated primitive-specific data for the primitive is not stored in the memory, calculating primitive-specific data for the primitive, using that calculated data to process the primitive, and storing at least some of the calculated primitive-specific data for the primitive for use after the primitive has been processed.