C# 判斷兩條直線是否相交

直接上代碼,過程不復雜

/// <summary>
/// 判斷兩條線是否相交
/// </summary>
/// <param name="a">線段1起點坐標</param>
/// <param name="b">線段1終點坐標</param>
/// <param name="c">線段2起點坐標</param>
/// <param name="d">線段2終點坐標</param>
/// <param name="intersection">相交點坐標</param>
/// <returns>是否相交 0:兩線平行  -1:不平行且未相交  1:兩線相交</returns>

private int GetIntersection(Point a, Point b, Point c, Point d ,ref Point intersection)
{
    //判斷異常
    if (Math.Abs(b.X - a.Y) + Math.Abs(b.X - a.X) + Math.Abs(d.Y - c.Y) + Math.Abs(d.X - c.X) == 0)
    {
        if (c.X - a.X == 0)
        {
           Debug.Print("ABCD是同一個點！"); 
        }
        else
        {
            Debug.Print("AB是一個點，CD是一個點，且AC不同！");
        }
        return 0;
    }

    if (Math.Abs(b.Y - a.Y) + Math.Abs(b.X - a.X) == 0)
    {
        if ((a.X - d.X) * (c.Y - d.Y) - (a.Y - d.Y) * (c.X - d.X) == 0)
        {
            Debug.Print ("A、B是一個點，且在CD線段上！");
        }
        else
        {
             Debug.Print ("A、B是一個點，且不在CD線段上！");
        }
        return 0;
    }

    if (Math.Abs(d.Y - c.Y) + Math.Abs(d.X - c.X) == 0)
    {
        if ((d.X - b.X) * (a.Y - b.Y) - (d.Y - b.Y) * (a.X - b.X) == 0)
        {
            Debug.Print ("C、D是一個點，且在AB線段上！");
        }
        else
        {
            Debug.Print ("C、D是一個點，且不在AB線段上！");
        }
    }


    if ((b.Y - a.Y) * (c.X - d.X) - (b.X - a.X) * (c.Y - d.Y) == 0)
    {
        Debug.Print ("線段平行，無交點！");
        return 0;
    }   

    intersection.X = ((b.X - a.X) * (c.X - d.X) * (c.Y - a.Y) - c.X * (b.X - a.X) * (c.Y - d.Y) + a.X * (b.Y - a.Y) * (c.X - d.X)) / ((b.Y - a.Y) * (c.X - d.X) - (b.X - a.X) * (c.Y - d.Y));
    intersection.Y = ((b.Y - a.Y) * (c.Y - d.Y) * (c.X - a.X) - c.Y * (b.Y - a.Y) * (c.X - d.X) + a.Y * (b.X - a.X) * (c.Y - d.Y)) / ((b.X - a.X) * (c.Y - d.Y) - (b.Y - a.Y) * (c.X - d.X));
   

    if ((intersection.X - a.X) * (intersection.X - b.X) <= 0 && (intersection.X - c.X) * (intersection.X - d.X) <= 0 && (intersection.Y - a.Y) * (intersection.Y - b.Y) <= 0 && (intersection.Y - c.Y) * (intersection.Y - d.Y) <= 0)
    {
        Debug.Print ("線段相交於點(" + intersection.X + "," + intersection.Y + ")！");
        return 1; //'相交
    }
    else
    {
        Debug.Print ("線段相交於虛交點(" + intersection.X + "," + intersection.Y + ")！");
        return -1; //'相交但不在線段上
    }
}