var size = 500;

function setup() {

  createCanvas(size+500, size);

  background(220);

}

​

function getIntersection(r, s){

  let r_px = r.a.x;

  let r_py = r.a.y;

  let r_dx = r.b.x - r.a.x;

  let r_dy = r.b.y - r.a.y;

  let s_px = s.a.x;

  let s_py = s.a.y;

  let s_dx = s.b.x - s.a.x;

  let s_dy = s.b.y - s.a.y;

  //Are they parallel?

  if(r_dx*s_dy == r_dy*s_dx){

    return null;

  }

  const T2 = (r_dx*(s_py-r_py) + r_dy*(r_px-s_px))/(s_dx*r_dy - s_dy*r_dx);

  const T1 = (s_py+s_dy*T2-r_py)/r_dy;

  if(T1 < 0){

    return null;

  }

  if(T2 < 0 || T2 > 1){

    return null;

  }

  return {

    x: r_px+r_dx*T1,

    y: r_py+r_dy*T1,

    param: T1

  };  

}

​

​

​

​

var segs = [

  //seg

  {a: {x:20, y:300}, b: {x: 250, y: 150}},

  {a: {x:200, y:300}, b: {x: 140, y: 100}},

  {a: {x:250, y:150}, b: {x: 140, y: 100}},

  {a: {x:320, y:300}, b: {x: 380, y: 300}},

  {a: {x:380, y:300}, b: {x: 380, y: 360}},

  {a: {x:380, y:360}, b: {x: 320, y: 360}},

  {a: {x:320, y:360}, b: {x: 320, y: 300}},

  //border

  {a: {x:0, y:0}, b: {x: size, y: 0}},

  {a: {x:0, y:0}, b: {x: 0, y: size}},

  {a: {x:size, y:0}, b: {x: size, y: size}},

  {a: {x:0, y:size}, b: {x: size, y: size}}

]

function draw() {

  background(0);

  stroke('red');

  strokeWeight(1);

//   for(let T1 = 0; T1 < 200; T1++){

//     let ray_x = 20+1*T1;

//     let ray_y = 30+1*T1;

//     point(ray_x, ray_y);

//   }

  //line(ray.a.x, ray.a.y, mouseX, mouseY);

  stroke('red');

  for(let seg of segs){

    line(seg.a.x, seg.a.y, seg.b.x, seg.b.y);

  }

  beginShape();

  for(let j = 0; j < PI*2; j+=PI*2/50){

    let ray = {a: {x: mouseX, y: mouseY}, b: {x: mouseX+sin(j), y: mouseY+cos(j)}};

    //Finding the closest intersection

    let closestIntersection = null;

    for(let seg of segs){

      let intersect = getIntersection(ray, seg);

      if(!intersect) continue;

      if(!closestIntersection || intersect.param < closestIntersection.param){

        closestIntersection = intersect;

      }

    }

    stroke('white');

    if(closestIntersection){

      line(ray.a.x, ray.a.y, closestIntersection.x, closestIntersection.y);

      //line(ray.a.x, ray.a.y, closestIntersection.b.x, closestIntersection.b.y);

     // vertex(closestIntersection.a.x, closestIntersection.a.y);

      //vertex(closestIntersection.b.x, closestIntersection.b.y);

      fill('white');

      circle(closestIntersection.x, closestIntersection.y, 5);

    }

  }

  endShape(CLOSE);

  // stroke(0);

  // for(let T2 = 0; T2 < 150; T2++){

  //   let s_dx = 1;

  //   let s_dy = -1;

  //   let seg_x = 20+s_dx*T2;

  //   let seg_y = 300+s_dy*T2;

  //   point(seg_x, seg_y);

  // }

}