1 PVector p1,p2,n;
 2 float d = 0;
 3 
 4 void setup()
 5 {
 6   size(600,600);
 7   
 8   p1 = new PVector(150,30);//線段第一個端點
 9   p2 = new PVector(-25,-100);//線段第二個端點
10   
11   PVector vec = PVector.sub(p1,p2);
12   vec.normalize();
13   n = new PVector(-vec.y,vec.x);//與線段垂直的向量
14   d = n.dot(p1);
15 }
16 
17 void
 
 draw()
18 {
19   background(#CCCCCC);
20   translate(300,300);//重置坐標原點
21   strokeWeight(1);
22   stroke(#000000);
23   line(-300,0, 300,0);//畫橫縱軸
24   line(0,-300, 0,300);
25   
26   drawLine(p1,p2);
27   drawVector(n);
28   
29   PVector q = new PVector(mouseX-300,mouseY-300);
30   strokeWeight(8);
31   stroke(#EEEE00);//yellow
32   point(q.x,q.y);
 
33   
34   float temp = d - q.dot(n);
35   PVector nearestPnt = new PVector(n.x,n.y);
36   nearestPnt.mult(temp);
37   nearestPnt.add(q);
38   
39   PVector delV1,delV2;//線段上的 最近點 到兩端點的向量
40   delV1 = PVector.sub(nearestPnt,p1);
41   delV2 = PVector.sub(nearestPnt,p2);
42   if(PVector.dot(delV1,delV2)>0)//
 
如果兩個向量的點積大於0，則最近點在線段外
43   {
44     nearestPnt = module(delV1)<module(delV2)?p1:p2;//則重置最近點到最近的端點
45   }
46   
47   drawLine(q,nearestPnt);
48 }
49 
50 //求向量的模
51 float module(PVector v)
52 {
53   return sqrt(pow(v.x,2)+pow(v.y,2));
54 }
55 
56 //畫一條綠色的線段，端點加粗
57 void drawLine(PVector p1,PVector p2)
58 {
59   strokeWeight(1);
60   stroke(0,155,0);
61   line(p1.x,p1.y, p2.x,p2.y);
62   strokeWeight(5);
63   point(p1.x,p1.y);
64   point(p2.x,p2.y);
65 }
66 
67 //畫一個紅色向量，原點開始
68 void drawVector(PVector v)
69 {
70   int k = 50;
71   strokeWeight(1);
72   stroke(255,0,0);
73   line(0,0, v.x*k,v.y*k);
74   strokeWeight(5);
75   point(0,0);
76 }

[Processing]點到線段的最小距離