1. A method performed by a PDM data processing system for providing hybrid hidden-line processing for a plurality of polygons representing tessellated image data, each polygon comprising a plurality of edges, the method comprising: generating a back-facing plate comprising polygons on a back-facing side of a silhouette of the tessellated image data and a front-facing plate comprising polygons on a front-facing side of the silhouette of the tessellated image data; tracing the edges; identifying at least one visibility change pixel in each of a subset of the traced edges; for each visibility change pixel, determining whether the traced edge is from the same plate as a polygon corresponding to the visibility change pixel; and for each traced edge that is determined to be from the same plate as the polygon corresponding to the visibility change pixel, displaying the traced edge.