在鼠标指针和一个点之间绘制一条跟踪线

Question

我有一个CAD应用程序。我有一流的线。

public class Line
{
    public float width { get; set; }
    public bool selected { get; set; }
    public Color color { get; set; }
    public Point Start { get; set; }
    public Point End { get; set; }

    public Line(Color col, float w, Point s, Point e)
    {

        color = col;
        Start = s;
        End = e;
        width = w;

    }
    public void Draw(Graphics G)
    {
        using (Pen pen = new Pen(color, width))
        {
            G.DrawLine(pen, Start, End);
        }
    }

我有一个名为Lines的列表。线条在面板上绘制

private void panel1_Paint(object sender, PaintEventArgs e)
        {
            Graphics grp = e.Graphics;
foreach (Line L in Lines.Except(DelLines))
            {
                L.Draw(grp);
            }
 if (mouseisdown && Line == true)
            {

                grp.DrawLine(Pens.White, DsP1, new Point(MousePosition.X, MousePosition.Y - 158));
                //     double d = Math.Abs((DsP1.X - MousePosition.X) + (DsP1.Y - (MousePosition.Y - 158)));
                if (snapON == true)
                {
                    grp.DrawLine(Pens.Yellow, snapPoint, mousePoint);

                }
           }

这里mousePoint是Point（mouseposition.X，mouseposition.Y-158）。 158是因为我的面板位于窗口顶部下方158°。然后我有一个mouseUp事件

   private void panel1_MouseUp(object sender, MouseEventArgs e)
    {
        mouseisdown = false;
        if (Line == true)
        {

            PointsList.Add(new Point(e.X, e.Y));
            Lines.Add(new PolygonArea.Line(Color.White, 1, DsP1, new Point(MousePosition.X, MousePosition.Y - 158)));
            Line = false;

        } }

现在我想在鼠标移动时绘制一条线，它将告诉鼠标位置它的x轴或y轴匹配线列表中一条线的点。我尝试的是：

在Panel1_MouseMove事件中

 if(Line==true && Lines.Count>1)
        {
                                if (Lines[0].Start.X == e.Location.X || 
Lines[0].Start.Y==e.Location.Y)
                {
                snapON = true;
                    snapPoint = Lines[0].Start;
                panel1.Invalidate();
                }
                else if(Lines[0].End.X==e.Location.X || Lines[0].End.Y == e.Location.Y)
                {
                snapON = true;
                    snapPoint = Lines[0].End;
                panel1.Invalidate();
                }
            }

仅供测试，我指的是行[0]中的第一行。但是当条件满足时，我无法在mousepointer和line的点之间画出一条线。任何的想法？？