/usr/share/radiance/bezier2.cal is in radiance-materials 4R0+20110410-1build1.
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Bicubic Bezier Patch
02Mar90
Define Px(i,j), Py(i,j), Pz(i,j)
}
x(s,t) = bezier(P2x(s,1), P2x(s,2), P2x(s,3), P2x(s,4), t);
y(s,t) = bezier(P2y(s,1), P2y(s,2), P2y(s,3), P2y(s,4), t);
z(s,t) = bezier(P2z(s,1), P2z(s,2), P2z(s,3), P2z(s,4), t);
P2x(s,j) = bezier(Px(1,j), Px(2,j), Px(3,j), Px(4,j), s);
P2y(s,j) = bezier(Py(1,j), Py(2,j), Py(3,j), Py(4,j), s);
P2z(s,j) = bezier(Pz(1,j), Pz(2,j), Pz(3,j), Pz(4,j), s);
bezier(p1, p2, p3, p4, t) = p1 * (1+t*(-3+t*(3-t))) +
p2 * 3*t*(1+t*(-2+t)) +
p3 * 3*t*t*(1-t) +
p4 * t*t*t ;
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