[Processing]点到线段的最小距离

PVector p1,p2,n;
float d = 0;

void setup()
{
  size(600,600);
  
  p1 = new PVector(150,30);//线段第一个端点
  p2 = new PVector(-25,-100);//线段第二个端点
  
  PVector vec = PVector.sub(p1,p2);
  vec.normalize();
  n = new PVector(-vec.y,vec.x);//与线段垂直的向量
  d = n.dot(p1);
}

void draw()
{
  background(#CCCCCC);
  translate(300,300);//重置坐标原点
  strokeWeight(1);
  stroke(#000000);
  line(-300,0, 300,0);//画横纵轴
  line(0,-300, 0,300);
  
  drawLine(p1,p2);
  drawVector(n);
  
  PVector q = new PVector(mouseX-300,mouseY-300);
  strokeWeight(8);
  stroke(#EEEE00);//yellow
  point(q.x,q.y);
  
  float temp = d - q.dot(n);
  PVector nearestPnt = new PVector(n.x,n.y);
  nearestPnt.mult(temp);
  nearestPnt.add(q);
  
  PVector delV1,delV2;//线段上的 最近点 到两端点的向量
  delV1 = PVector.sub(nearestPnt,p1);
  delV2 = PVector.sub(nearestPnt,p2);
  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
  {
    nearestPnt = module(delV1)<module(delV2)?p1:p2;//则重置最近点到最近的端点
  }
  
  drawLine(q,nearestPnt);
}

//求向量的模
float module(PVector v)
{
  return sqrt(pow(v.x,2)+pow(v.y,2));
}

//画一条绿色的线段，端点加粗
void drawLine(PVector p1,PVector p2)
{
  strokeWeight(1);
  stroke(0,155,0);
  line(p1.x,p1.y, p2.x,p2.y);
  strokeWeight(5);
  point(p1.x,p1.y);
  point(p2.x,p2.y);
}

//画一个红色向量，原点开始
void drawVector(PVector v)
{
  int k = 50;
  strokeWeight(1);
  stroke(255,0,0);
  line(0,0, v.x*k,v.y*k);
  strokeWeight(5);
  point(0,0);
}