在兩點之間畫線並在兩側延長線

Question

我有下面的代碼，它允許我在兩個給定點之間畫一條線。 我需要做的是雙向延伸這些線，以便線以相同的角度延伸到線的兩端

private void Form1_Load(object sender, EventArgs e)
{
    this.Controls.Add(new Panel{Left = 10, Top = 10,Width = 50,Height = 50, BackColor = Color.Blue});
    this.Controls.Add(new Panel {Left = 100, Top = 100,Width = 50,Height = 50, BackColor = Color.Blue});


}
protected override void OnPaint(PaintEventArgs e)
{
    base.OnPaint(e);
    Graphics g;
    g = e.Graphics;
    Pen myPen = new Pen(Color.Red);
    myPen.Width = 1;
    g.DrawLine(myPen, 12, 12, 45, 65);
    g.DrawLine(myPen, 100, 100, 45, 65);
}

Answer 1

嘗試使用以下方法：

startPoint 和 endPoint 是著名的點。 p1 和 p2 是新的起點和終點。

 public static void FindSimmetricPointsOnLine(Point startPoint, Point endPoint, double distance, out Point p1, out Point p2)
        {
            p1 = new Point();
            p2 = new Point();
            var xa = startPoint.X;
            var ya = startPoint.Y;
            var xb = endPoint.X;
            var yb = endPoint.Y;
            var l = distance;
            double x1 = 0;
            double x2 = 0;
            double y1 = 0;
            double y2 = 0;


            if (xa == xb)
            {
                x1 = x2 = xa;
                y1 = ya + l;
                y2 = ya - l;
            }
            else
            {
                if (ya == yb)
                {
                    y1 = y2 = ya;
                    x1 = xa + l;
                    x2 = xa - l;
                }
                else
                {
                    var K = (ya - yb)/(xa - xb);
                    var B = ya - K*xa;
                    var A1 = K*K + 1;
                    var B1 = -2*(xa + K*(ya - B));
                    var C1 = xa*xa + (ya - B)*(ya - B) - l*l;
                    var D = B1*B1 - 4*A1*C1;

                    if (D >= 0)
                    {
                        x1 = (-B1 + Math.Sqrt(D))/(2*A1);
                        x2 = (-B1 - Math.Sqrt(D))/(2*A1);


                        y1 = K*x1 + B;
                        y2 = K*x2 + B;

                        p1 = new Point(x1, y1);
                        p2 = new Point(x2, y2);
                    }
                }
            }
        }

Answer 2

這里有一些代碼應該可以滿足您的需求。

public void ExtendLine(Point p1, Point p2, double distance, out Point start, out Point end)
{
    //first find the vector that represents the direction of the line
    Vector direction = p2 - p1;

    //normalize the vector to a distance of one point
    direction.Normalize();

    //multiply the direction by to total distance to find the offset amount
    Vector offset = (direction * distance);

    //subtract the offset from the start point to find the new start point
    start = p1 - offset;

    //add the offset to the end point to find the new end point
    end = p2 + offset;
}

這是一個顯示如何使用該方法的示例。

Point p1 = new Point(Line1.X1, Line1.Y1), p2 = new Point(Line1.X2, Line1.Y2);
ExtendLine(p1, p2, 10, out Point p3, out Point p4);
Line2.X1 = p3.X;
Line2.Y1 = p3.Y;
Line2.X2 = p4.X;
Line2.Y2 = p4.Y;