[Processing]點到線段的最小距離

 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);//重置座標原點
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)//若是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 }