When generating a graphics processing output by assembling a sequence of one or more of primitives to be processed from a set of vertex indices provided for the output based on primitive configuration information provided for the output, one or more vertex packets are generated using the vertex indices for the assembled primitives, each vertex packet comprising a plurality of vertices of the assembled primitives. After a threshold number of vertices have been allocated to a vertex packet, vertex attribute processing for the vertices of the vertex packet is triggered, to thereby generate a vertex packet comprising processed vertex attributes for the vertices of the vertex packet. The assembled primitives and the generated vertex packets are then provided to later stages of the graphics processing pipeline for processing.