function init() {
  class Point {
    constructor(x, y) {
      this.x = x;
      this.y = y;
    }

    add(that) {
      return new Point(
        this.x + that.x,
        this.y + that.y
      );
    }

    sub(that) {
      return new Point(
        this.x - that.x,
        this.y - that.y
      );
    }

    dist(that) {
      let a = this.x - that.x;
      let b = this.y - that.y;
      return Math.sqrt(a * a + b * b)
    }
  }

  function vectorLength(a, b) {
    let v1 = new THREE.Vector3();
    v1.set(a.x, a.y, a.z);
    let v2 = new THREE.Vector3();
    v2.set(b.x, b.y, b.z);

    return v1.sub(v2).length();
  }

  class Face {
    a;
    b;
    c;
    d;

    springs = [];

    constructor(a, b, c, d) {
      this.a = a;
      this.b = b;
      this.c = c;
      this.d = d;
    }
  }

  class Spring {
    restLength;
    currentLength;
    index1;
    index2;

    constructor(vertices, index1, index2) {
      this.index1 = index1;
      this.index2 = index2;

      let length = vectorLength(vertices[index1], vertices[index2]);
      this.restLength = length;
      this.currentLength = length;
    }
  }

  class Cloth {
    VertexWeight = 1;

    geometry = new THREE.Geometry();

    faces = [];

    vertexWeights = [];

    createBasic(width, height, numPointsWidth, numPointsHeight) {
      let vertices = [];
      let faces = [];

      let stepWidth = width / (numPointsWidth - 1);
      let stepHeight = height / (numPointsHeight - 1);

      for (let y = 0; y < numPointsHeight; y++) {
        for (let x = 0; x < numPointsWidth; x++) {
          vertices.push(
            new THREE.Vector3(x * stepWidth, height - y * stepHeight, 0)
          );
        }
      }

      function getVertexIndex(x, y) {
        return y * numPointsWidth + x;
      }
      
      for (let y = 0; y < numPointsHeight - 1; y++) {
        for (let x = 0; x < numPointsWidth - 1; x++) {
          let newFace = new Face(
            getVertexIndex(x, y),
            getVertexIndex(x, y + 1),
            getVertexIndex(x + 1, y),
            getVertexIndex(x + 1, y + 1),
          );

          newFace.springs.push(new Spring(vertices, getVertexIndex(x, y), getVertexIndex(x + 1, y)));
          newFace.springs.push(new Spring(vertices, getVertexIndex(x, y), getVertexIndex(x, y + 1)));
          newFace.springs.push(new Spring(vertices, getVertexIndex(x, y), getVertexIndex(x + 1, y + 1)));
          newFace.springs.push(new Spring(vertices, getVertexIndex(x + 1, y), getVertexIndex(x, y + 1)));
          newFace.springs.push(new Spring(vertices, getVertexIndex(x + 1, y), getVertexIndex(x + 1, y + 1)));
          newFace.springs.push(new Spring(vertices, getVertexIndex(x, y + 1), getVertexIndex(x + 1, y + 1)));
          
          faces.push(newFace);
        }
      }

      this.createExplicit(vertices, faces);
    }

    createExplicit(vertices, faces) {
      for (let i in vertices) {
        this.geometry.vertices.push(vertices[i]);
        this.vertexWeights.push(0);
      }
      for (let i in faces) {
        let face = faces[i];

        this.faces.push(face);

        this.geometry.faces.push(new THREE.Face3(
          face.a, face.b, face.c
        ));
        this.geometry.faces.push(new THREE.Face3(
          face.c, face.b, face.d
        ));
        
        let xLength = vectorLength(this.geometry.vertices[face.b], this.geometry.vertices[face.a]);
        let yLength = vectorLength(this.geometry.vertices[face.c], this.geometry.vertices[face.a]);
        let weight = xLength * yLength / 2;

        xLength = vectorLength(this.geometry.vertices[face.b], this.geometry.vertices[face.d]);
        yLength = vectorLength(this.geometry.vertices[face.c], this.geometry.vertices[face.d]);
        weight += xLength * yLength / 2;

        this.vertexWeights[face.a] += weight / 4;
        this.vertexWeights[face.b] += weight / 4;
        this.vertexWeights[face.c] += weight / 4;
        this.vertexWeights[face.d] += weight / 4;
      }

      this.geometry.computeBoundingSphere();
    }

    createDebugMesh(scene) {
      function addLine(from, to, color) {
        let geometry = new THREE.Geometry();
        geometry.vertices.push(from);
        geometry.vertices.push(to);
        let material = new THREE.LineBasicMaterial( { color: color, linewidth: 10 } );
        let line = new THREE.Line(geometry, material);
        line.renderOrder = 1;
        scene.add(line);
      }
      function addPoint(point, color) {
        const geometry = new THREE.SphereGeometry( 0.05, 32, 32 );
        const material = new THREE.MeshBasicMaterial( { color: color } );
        const sphere = new THREE.Mesh( geometry, material );
        sphere.position.set(point.x, point.y, point.z);
        scene.add( sphere );
      }

      let lineColor = 0x000000;
      let pointColor = 0xff00000;

      for (let i in this.faces) {
        let face = this.faces[i];
        addLine(this.geometry.vertices[face.a], this.geometry.vertices[face.b], lineColor);
        addLine(this.geometry.vertices[face.a], this.geometry.vertices[face.c], lineColor);
        addLine(this.geometry.vertices[face.a], this.geometry.vertices[face.d], lineColor);
        addLine(this.geometry.vertices[face.b], this.geometry.vertices[face.c], lineColor);
        addLine(this.geometry.vertices[face.b], this.geometry.vertices[face.d], lineColor);
        addLine(this.geometry.vertices[face.c], this.geometry.vertices[face.d], lineColor);

        addPoint(this.geometry.vertices[face.a], pointColor);
        addPoint(this.geometry.vertices[face.b], pointColor);
        addPoint(this.geometry.vertices[face.c], pointColor);
        addPoint(this.geometry.vertices[face.d], pointColor);
      }
    }
  }

  let mousePos = new Point();

  const canvasSpace = 200;

  const scene = new THREE.Scene();
  const camera = new THREE.PerspectiveCamera(75, window.innerWidth / (window.innerHeight - canvasSpace), 0.1, 1000);

  const renderer = new THREE.WebGLRenderer();
  renderer.setSize(window.innerWidth, window.innerHeight - canvasSpace);
  document.getElementById("threejscontainer").appendChild(renderer.domElement);

  const directionalLight = new THREE.DirectionalLight(0xffffff, 1);
  scene.add(directionalLight);

  let cloth = new Cloth();
  cloth.createBasic(10, 10, 5, 5);
  cloth.createDebugMesh(scene);

  const material = new THREE.MeshBasicMaterial({ color: 0x0000ff });
  const mesh = new THREE.Mesh(cloth.geometry, material);
  scene.add(mesh);

  camera.position.y = 5;
  camera.position.z = 10;
  //camera.lookAt(new THREE.Vector3(1, 0, 0));

  function animate(dt) {
    requestAnimationFrame(animate);
    renderer.render(scene, camera);
  }

  let canvas = document.getElementsByTagName("canvas")[0];
  let resize = function () {
    w = window.innerWidth;
    h = window.innerHeight - 200;
    canvas.width = w;
    canvas.height = h;
  }
  window.onresize = resize;
  resize();
  if (canvas.getContext) {
    animate(performance.now());
  }
  canvas.onmousemove = (evt) => {
    mousePos.x = evt.clientX;
    mousePos.y = evt.clientY;
  };
}