1. A method for compressing a list of primitives in a computer graphics system from a tessellated patch of surface data, the method comprising the steps of: a) receiving domain point indices for a first primitive in a list of primitives defining the tessellated patch; b) storing the domain point indices for the received primitive in a buffer; c) comparing domain point indices of a next primitive in the list with the domain point indices stored in the buffer and determining any matches; d) storing in the buffer the domain point indices of the next primitive, or, where a match was found in the buffer, storing a reference to the position of the matched index; e) receiving domain point indices of a next primitive in the list f) repeating steps c) to f) until each primitive in the list of primitives has been compressed; wherein the step of storing the domain point indices in the buffer includes the storage of a further predicted domain point index which is computed from the domain point indices stored in the buffer; and, outputting compressed domain point indices for the tessellated patch from the buffer.