[Processing]点到线段的最小距离

Posted 2020-12-02 yukisora

 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);//线段第一个端点
 9   p2 = new PVector(-25,-100);//线段第二个端点
10   
11   PVector vec = PVector.sub(p1,p2);
12   vec.normalize();
13   n = new PVector(-vec.y,vec.x);//与线段垂直的向量
14   d = n.dot(p1);
15 }
16 
17 void draw()
18 {
19   background(#CCCCCC);
20   translate(300,300);//重置坐标原点
21   strokeWeight(1);
22   stroke(#000000);
23   line(-300,0, 300,0);//画横纵轴
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;//线段上的 最近点 到两端点的向量
40   delV1 = PVector.sub(nearestPnt,p1);
41   delV2 = PVector.sub(nearestPnt,p2);
42   if(PVector.dot(delV1,delV2)>0)//如果两个向量的点积大于0，则最近点在线段外
43   {
44     nearestPnt = module(delV1)<module(delV2)?p1:p2;//则重置最近点到最近的端点
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 //画一条绿色的线段，端点加粗
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 //画一个红色向量，原点开始
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 }