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unity 凸多形顶点排序

/// <summary>
/// 多边形点集排序
/// </summary>
/// <param name="vPoints"></param>
/// <returns></returns>
public List<Point> SortPolyPoints(List<Point> vPoints)
{
    if (vPoints == null || vPoints.Count == 0) return null;
    //计算重心
    Point center = new Point();
    double X = 0, Y = 0;
    for (int i = 0; i < vPoints.Count; i++)
    {
        X += vPoints[i].X;
        Y += vPoints[i].Y;
    }
    center = new Point((int)X / vPoints.Count, (int)Y / vPoints.Count, vPoints[0].Z);
    //冒泡排序
    for (int i = 0; i < vPoints.Count - 1; i++)
    {
        for (int j = 0; j < vPoints.Count - i - 1; j++)
        {
            if (PointCmp(vPoints[j], vPoints[j + 1], center))
            {
                Point tmp = vPoints[j];
                vPoints[j] = vPoints[j + 1];
                vPoints[j + 1] = tmp;
            }
        }
    }
    return vPoints;
}

/// <summary>
/// 若点a大于点b,即点a在点b顺时针方向,返回true,否则返回false
/// </summary>
/// <param name="a"></param>
/// <param name="b"></param>
/// <param name="center"></param>
/// <returns></returns>
private bool PointCmp(Point a, Point b, Point center)
{
    if (a.X >= 0 && b.X < 0)
        return true;
    else if (a.X == 0 && b.X == 0)
        return a.Y > b.Y;
    //向量OA和向量OB的叉积
    double det = (a.X - center.X) * (b.Y - center.Y) - (b.X - center.X) * (a.Y - center.Y);
    if (det < 0)
        return true;
    if (det > 0)
        return false;
    //向量OA和向量OB共线,以距离判断大小
    double d1 = (a.X - center.X) * (a.X - center.X) + (a.Y - center.Y) * (a.Y - center.Y);
    double d2 = (b.X - center.X) * (b.X - center.X) + (b.Y - center.Y) * (b.Y - center.Y);
    return d1 > d2;
}

posted on 2021-02-20 15:52  kingBook  阅读(28)  评论(0编辑  收藏