When rendering a region of a three-dimensional object represented by a base set of polygon vertices in a graphics processing pipeline, a first processing stage uses meta-information representative of the surface relief of the region of the three-dimensional object to determine whether to generate a set of additional polygon vertices over the region of the three-dimensional object, and generates the additional set of polygon vertices (when this is deemed necessary). A second processing stage then uses information representative of the surface relief of the region of the three-dimensional object to modify the positions of one or more of the polygon vertices, before the vertices are assembled into primitives that are then rasterised and rendered.