Path drawing

by ikatyang

HTML

<script src="https://cdnjs.cloudflare.com/ajax/libs/three.js/r76/three.min.js"></script>
<script src="https://dl.dropboxusercontent.com/u/3587259/Code/Threejs/OrbitControls.js"></script>

CSS

body {
  margin: 0;
  overflow: hidden;
}

JavaScript

var camera, scene, renderer, controls;
var ball;

init();
animate();

function init() {

  scene = new THREE.Scene();

  camera = new THREE.PerspectiveCamera(50, window.innerWidth / window.innerHeight, 1, 20000);
  camera.position.set(0, 300, 500);
  scene.add(camera);

  ball = new THREE.Mesh(new THREE.SphereGeometry(5, 12, 12));
  ball.position.set(-100, 0, 0);
  ball.velocity = new THREE.Vector3(1, 2, 0).setLength(500);
  scene.add(ball);

 	var gridXZ = new THREE.GridHelper(200, 20, 0xff0000, 0x88888888);
  scene.add(gridXZ);

  renderer = new THREE.WebGLRenderer();
  renderer.setClearColor(0xffffff);
  renderer.setSize(window.innerWidth, window.innerHeight);

  controls = new THREE.OrbitControls(camera, renderer.domElement);

  document.body.appendChild(renderer.domElement);
  window.addEventListener('resize', onWindowResize, false);
}

function onWindowResize() {
  camera.aspect = window.innerWidth / window.innerHeight;
  camera.updateProjectionMatrix();
  renderer.setSize(window.innerWidth, window.innerHeight);
}

function updatePosition(delta) {
	var force = new THREE.Vector3(0, -980, 0);
  ball.velocity.addScaledVector(force, delta);
  ball.position.addScaledVector(ball.velocity, delta);
}

function animate() {
  if (ball.position.y >= 0) {
    var posPrev = ball.position.clone();
    updatePosition(1 / 60 / 5);
    var posNext = ball.position.clone();
  	scene.add(createLine(posPrev, posNext, 5, 'red'));
  }
  controls.update();
  requestAnimationFrame(animate);
  renderer.render(scene, camera);
}

function createLine(start, end, size, color) {
  var line = new THREE.Object3D();
  var distance = start.clone().sub(end).length();
  var box = new THREE.Mesh(
    new THREE.BoxGeometry(size, size, distance),
    new THREE.MeshBasicMaterial({ color: color }));
  box.position.z = distance / 2;
  line.add(box);
  line.position.copy(start);
  line.lookAt(end);
  return line;
}