Disclosed herein is a bounding box that can be generated for a set of one or more primitive(s) and then passed to a rasteriser circuit for use thereby when generating the graphics fragments to be processed. The bounding box generation integrates a scissor test and allows primitives for which an initial bounding box has zero intersection with a specified scissor box to be discarded, whereas for primitives whose initial bounding box does intersect the scissor box, a new bounding box can be generated for output based on the area of intersection.