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);//yellow32   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)