The shape of a polygon is given by the amplitude pattern of the surface function of Eq. (1). Thus, the distribution that provides shape to the polygon is given by Display Formula
$Ishape,n(xn,yn)={1\u2026inside polygon0\u2026outside polygon.$(6)
In the polygon-based method, the shading technique for the object surface is essentially the same as that of CG. The distribution for shading is given by Display Formula$Ishade,n(xn,yn)=Is,n(xn,yn)+Ienv,$(7)
where $Ienv$ gives the degree of ambient light. When flat-shading is used, the distribution $Is,n(xn,yn)$ is a constant and given by Lambert’s cosine law: Display Formula$Is,n(xn,yn)\u2261Nn\xb7Li,$(8)
where $Nn$ and $Li$ are the normal vector of the polygon $n$ and a unit vector pointing from the surface to the virtual light source of the 3D scene.