1. A method, performed in a processing apparatus, of processing data defining at least three two-dimensional rectangular texture maps to generate data defining a single two-dimensional rectangular texture map containing all of the starting texture maps, the method comprising: combining two of the texture maps by arranging them adjacent each other with an edge of one texture map parallel to an edge of the other texture map, and defining a rectangle containing the two texture maps, thereby generating a new texture map for subsequent combination; and repeating the combining processing to combine texture maps in pairs, to generate a single two-dimensional rectangle containing the starting texture maps.