A graphics processing system for generating a rendering output includes geometry processing logic and rasterization logic. The geometry processing logic includes first transformation logic configured to transform a plurality of untransformed primitives into a plurality of transformed primitives, the first transformation logic configured to implement one or more expansion transformation stages which generate one or more sub-primitives; a primitive block generator configured to: divide the plurality of transformed primitives into a plurality of groups; and generate an untransformed primitive block for each group comprising (i) information identifying the untransformed primitives related to the transformed primitives in the group; and (ii) an expansion transformation stage mask for at least one of the one or more expansion transformation stages that indicates the sub-primitives generated for the untransformed primitives in that untransformed primitive block that are to be used in generating the rendering output. The rasterization logic comprising: second transformation logic configured to re-transform the plurality of untransformed primitives into the plurality of transformed primitives on an untransformed primitive block-basis in accordance with the expansion transformation stage mask for the at least one of the one or more expansion transformation stages; and logic configured to render the transformed primitives to generate the rendering output.