Abstract: There is provided a graphics primitive assembly circuit comprising an early primitive assembly data generator operable to supply primitive input to a shader and a buffer operable to store early primitive assembly data during operation of the shader and to supply the early primitive assembly data to a late primitive assembly circuit element responsive to completion of operation of the shader. The circuit may also include a compressor that compresses the early primitive assembly data to reduce the amount of storage taken up by the buffer and the bandwidth required to transfer the early primitive assembly data.