1. A graphics system for rendering an image on a display device, the graphics system comprising: a buffer memory; a first unit configured to (a) receive three vertices corresponding to a triangle, (b) compute edge displacements for each edge of the triangle based on the three vertices, (c) determine a first ordering code and a second ordering code corresponding respectively to a first ordering and a second ordering of the vertices and edge displacements in response to sign bits of the edge displacements, (d) store the vertices, edge displacements, first ordering code and second ordering code in the buffer memory; and a second unit configured to access and operate on said vertices and edge displacements from the buffer memory to determine axial ordinate rate values for the triangle, wherein said second unit accesses said vertices and edge displacements from the buffer memory according to the first and second orderings using the first and second ordering codes respectively; wherein said axial ordinate rate values are usable to determine a portion of a displayable image.