カスタムPolyframe

//
// 前後のポイント座標差を進行ベクトルとする
// Run Over: Primitive
// 
int pts[] = primpoints(0, @primnum);

// プリミティブが閉じているか否か
int isClosed = primintrinsic(0, "closed", 0);

for(int i = 0; i < len(pts); i++)
{
    vector p0 = point(0, "P", pts[i-1]);
    vector p1 = point(0, "P", pts[i+1]);

    // 始点
    if(i == 0)
    {
        if(isClosed)
            p0 = point(0, "P", pts[-1]);
        else
            p0 = point(0, "P", pts[0]);
        p1 = point(0, "P", pts[i+1]);
    }
    // 終点
    else if(i == len(pts)-1)
    {
        p0 = point(0, "P", pts[i-1]);
        if(isClosed)
            p1 = point(0, "P", pts[0]);
        else
            p1 = point(0, "P", pts[i]);
    }
    
    vector n = normalize(p1 - p0);
    vector up = set(0, 1, 0);
    vector left = cross(up, n);
    up = cross(n, left);
    
    setpointattrib(0, "N", pts[i], n);
    setpointattrib(0, "up", pts[i], up);
}