150行JavaScript代码实现增强现实

增强现实技术（Augmented Reality，简称 AR），是一种实时地计算摄影机影像的位置及角度并加上相应图像、视频、3D模型的技术，这种技术的目标是在屏幕上把虚拟世界套在现实世界并进行互动。这种技术1990年提出。随着随身电子产品CPU运算能力的提升，预期增强现实的用途将会越来越广。

本文介绍使用JavaScript开源框架AR.js实现的增强现实的Hello World例子。

先看效果：

首先在手机浏览器里打开我部署在github page上的这个demo应用：

https://i042416.github.io/FioriODataTestTool2014/WebContent/098_ar.html

我用的是Android手机安装的Chrome浏览器。

打开网页，会提示你是否允许这个网页应用访问您的手机摄像头。点击允许：

用手机上的摄像头扫描这张图片：

神奇的事情就发生了。您会看到，通过手机摄像头望过去，手机屏幕里会出现一个新的不断滚动的3D物体，如下图所示。

下面具体介绍这个最简单的例子是怎么开发出来的。

所有的源代码在我的github上：

https://github.com/i042416/FioriODataTestTool2014/tree/master/WebContent/ar

新建一个html文件，把下列150行代码粘贴进去，然后在服务器上运行，使用之前描述的步骤即可进行AR测试：

<!DOCTYPE html>
<meta name="viewport" content="width=device-width, user-scalable=no, minimum-scale=1.0, maximum-scale=1.0">

<script src='ar/lib/three.min.js'></script>
<script src="ar/lib/stats.min.js"></script>
<script src="ar/lib/ar.js"></script>

<script>
debugger;
 THREEx.ArToolkitContext.baseURL = '';
</script>
<body style='margin : 0px; overflow: hidden; font-family: Monospace;'>
<div style='position: absolute; top: 10px; width:100%; text-align: center; z-index: 1;'>

<script>

	var renderer	= new THREE.WebGLRenderer({
		// antialias	: true,
		alpha: true
	});
	renderer.setClearColor(new THREE.Color('lightgrey'), 0)
	// renderer.setPixelRatio( 1/2 );
	renderer.setSize( window.innerWidth, window.innerHeight );
	renderer.domElement.style.position = 'absolute'
	renderer.domElement.style.top = '0px'
	renderer.domElement.style.left = '0px'
	document.body.appendChild( renderer.domElement );

	// array of functions for the rendering loop
	var onRenderFcts= [];

	// init scene and camera
	var scene	= new THREE.Scene();
	
	var camera = new THREE.Camera();
	scene.add(camera);
	
	var arToolkitSource = new THREEx.ArToolkitSource({
		// to read from the webcam 
		sourceType : 'webcam',

		// to read from an image
		// sourceType : 'image',
		// sourceUrl : THREEx.ArToolkitContext.baseURL + '../data/images/img.jpg',		

		// to read from a video
		// sourceType : 'video',
		// sourceUrl : THREEx.ArToolkitContext.baseURL + '../data/videos/headtracking.mp4',		
	})

	arToolkitSource.init(function onReady(){
		onResize()
	})
	
	window.addEventListener('resize', function(){
		onResize()
	})
	function onResize(){
		arToolkitSource.onResize()	
		arToolkitSource.copySizeTo(renderer.domElement)	
		if( arToolkitContext.arController !== null ){
			arToolkitSource.copySizeTo(arToolkitContext.arController.canvas)	
		}	
	}

	var arToolkitContext = new THREEx.ArToolkitContext({
		// cameraParametersUrl: THREEx.ArToolkitContext.baseURL + '../data/data/camera_para.dat',
		cameraParametersUrl: 'ar/data/data/camera_para.dat',
		detectionMode: 'mono',
		maxDetectionRate: 30,
		canvasWidth: 80*3,
		canvasHeight: 60*3,
	})

	arToolkitContext.init(function onCompleted(){
		camera.projectionMatrix.copy( arToolkitContext.getProjectionMatrix() );
	})

	onRenderFcts.push(function(){
		if( arToolkitSource.ready === false )	
			return;
		arToolkitContext.update( arToolkitSource.domElement )
	})
	
	var markerRoot = new THREE.Group
	scene.add(markerRoot)
	var artoolkitMarker = new THREEx.ArMarkerControls(arToolkitContext, markerRoot, {
		type : 'pattern',
		patternUrl : THREEx.ArToolkitContext.baseURL + 'ar/data/data/patt.hiro'
	})

	// build a smoothedControls
	var smoothedRoot = new THREE.Group()
	scene.add(smoothedRoot)
	var smoothedControls = new THREEx.ArSmoothedControls(smoothedRoot, {
		lerpPosition: 0.4,
		lerpQuaternion: 0.3,
		lerpScale: 1,
	})
	onRenderFcts.push(function(delta){
		smoothedControls.update(markerRoot)
	})

	var arWorldRoot = smoothedRoot

	// add a torus knot	
	var geometry	= new THREE.CubeGeometry(1,1,1);
	var material	= new THREE.MeshNormalMaterial({
		transparent : true,
		opacity: 0.5,
		side: THREE.DoubleSide
	}); 
	var mesh	= new THREE.Mesh( geometry, material );
	mesh.position.y	= geometry.parameters.height/2
	arWorldRoot.add( mesh );
	
	var geometry	= new THREE.TorusKnotGeometry(0.3,0.1,64,16);
	var material	= new THREE.MeshNormalMaterial(); 
	var mesh	= new THREE.Mesh( geometry, material );
	mesh.position.y	= 0.5
	arWorldRoot.add( mesh );
	
	onRenderFcts.push(function(){
		mesh.rotation.x += 0.1
	})

	var stats = new Stats();
	document.body.appendChild( stats.dom );
	// render the scene
	onRenderFcts.push(function(){
		renderer.render( scene, camera );
		stats.update();
	})

	// run the rendering loop
	var lastTimeMsec= null
	requestAnimationFrame(function animate(nowMsec){
		// keep looping
		requestAnimationFrame( animate );
		// measure time
		lastTimeMsec	= lastTimeMsec || nowMsec-1000/60
		var deltaMsec	= Math.min(200, nowMsec - lastTimeMsec)
		lastTimeMsec	= nowMsec
		// call each update function
		onRenderFcts.forEach(function(onRenderFct){
			onRenderFct(deltaMsec/1000, nowMsec/1000)
		})
	})
</script></body>