Patent Document ID: 4855938
Application ID: 07115455
Patent Status: 1

Claim One:
1. A method for producing a wire-frame graphics display in two dimensions and without hidden lines in a graphics display system having a depth buffer and a frame buffer each containing a storage location for each displayable point on said display system, said display to be as it would appear from a chosen viewpoint and said display to be produced from data representing the vertices of a set of polygons defining a three-dimensional object and its projection onto a view plane, said method comprising the steps of: (1) initializing each location in the depth buffer to a depth value corresponding to the farthest position from the viewpoint which can be displayed by the system and reserving the value ZCLOSE representing the closest position to the viewpoint which can be displayed by the system; (2) processing each projected polygon in turn in the following way: (a) computing the depth value of each point on each polygon edge and its corresponding storage location in the depth buffer; (b) comparing each computed depth value with the value then stored in the corresponding depth buffer storage location; (c) replacing the corresponding depth buffer value with the value ZCLOSE if the computed depth value represents a position closer to the viewpoint than the stored value; (d) tessellating the polygon into a set of triangles; (e) for each triangle: (i) computing the depth value of each point of the triangle and its corresponding storage location in the depth buffer; (ii) comparing each computed depth value with the value then stored in the corresponding depth buffer storage location; (iii) replacing the corresponding depth buffer value with the computed depth value and writing the frame buffer with a background color value if the computed depth value represents a position closer to the viewpoint than the stored value; (f) computing a second time the depth value of each point on each polygon edge and its corresponding storage location in the depth buffer; (g) comparing said second computed depth value with the value then stored in the corresponding depth buffer storage location; (h) replacing the depth buffer value with the second computed depth value for said polygon edge point and writing the frame buffer with a foreground color value if the value then stored therein is equal to ZCLOSE or if the second computed depth value represents a position closer to the viewpoint than the stored value.