150行JavaScript代码实现增强现实

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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>