1. A method of operating a graphics processing pipeline that includes a rasteriser that rasterises input primitives to generate graphics fragments to be processed, each graphics fragment having one or more sampling points associated with it, and a renderer that processes fragments generated by the rasteriser to generate output fragment data for output to a render output, the method comprising: when processing a graphics primitive to generate a render output: (i) determining first primitive set-up information to be used to test whether at least a part of the primitive should be processed further; (ii) using at least some of the first primitive set-up information to decide whether to process at least a part of the primitive further; and if it is decided that at least a part of the primitive is to be processed further: (iii) determining second primitive set-up information to be used to test whether at least a part of the primitive should be processed further; and (iv) using at least some of the second primitive set-up information to decide whether to process at least a part of the primitive further; wherein the second primitive set-up information comprises at least one edge equation for the primitive and step (iv) comprises determining if the primitive is located at least partially within a region of the render output, using the second primitive set-up information.