CIRCUIT FOR DETERMINING NON-HOMOGENOUS SECOND ORDER PERSPECTIVE TEXTURE MAPPING COORDINATES USING LINEAR INTERPOLATION

摘要

A texture value determining (TVD) circuit approximates non- homogenous 2nd order perspective texture mapping to provide texture for a polygon using linear interpolation and input parameters. The TVD circuit of the present invention includes a vertical walk subcircuit and an orthogonal walk subcircuit. The vertical walk subcircuit determines texture coordinates, u(a.sub.0,n) and v(a.sub.0,n) that represent the pixels along a vertical main slop of a triangle polygon. The orthogonal walk subcircuit determines texture coordinates, u(a.sub.m,n) and v(a.sub. m,n), for orthogonally walked polygon coordinate positions for which m 0. The orthogonally walked coordinate positions represent individual scan lines. The vertical walk subcircuit of the TVD circuit includes adders, latches, and accumulators. Each element of the vertical walk subcircuit receives a vertical main slope clock (n-clock) signal. An output of the vertical walk subsystem is computed based on the relationship,P Pu(a.sub.0,n)=u(a.sub.0, n-1)+du.sub.main + (n-1)d.sup. 2 u.sub. main for m=0, n 0PPwhere du.sub. main and d.sup.2 u. sub. main are input parameters. The orthogonal walk subcircuit also includes adders, latches, and accumulators. The orthogonal walk subcircuit is clocked by an orthogonal walk (m-clock) signal as well as the n-clock signal. An output of the orthogonal walk subcircuit is computed based on the relationship,PPu(a. sub.m,n)=u(a.sub. m-1, n)+n(du.sub.ortho-ADD)+ du.sub.ortho +(m-1)d.sup.2 u.sub.ortho for m 0PPwhere du.sub. ortho -ADD and du. sub.ortho and d. sup.2 u.sub.ortho are input parameters.