JerryWang_SAP 阅读(21) 评论(0)

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>
 

当然,这个效果来自大神jeromeetienne开源的AR.js:

https://github.com/jeromeetienne/AR.js/

当然大神自己也很谦虚地提到,他这个开源的增强现实框架也是建立在巨人的肩膀上开发的:比如其中3D效果的绘制,使用到了另一个开源框架three.js:

 

要获取更多Jerry的原创文章,请关注公众号"汪子熙":