150行JavaScript代碼實現加強現實

時間 2019-11-11

原文原文鏈接

加強現實技術（Augmented Reality，簡稱 AR），是一種實時地計算攝影機影像的位置及角度並加上相應圖像、視頻、3D模型的技術，這種技術的目標是在屏幕上把虛擬世界套在現實世界並進行互動。這種技術1990年提出。隨着隨身電子產品CPU運算能力的提高，預期加強現實的用途將會愈來愈廣。html

本文介紹使用JavaScript開源框架AR.js實現的加強現實的Hello World例子。git

先看效果：github

首先在手機瀏覽器裏打開我部署在github page上的這個demo應用：web

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

我用的是Android手機安裝的Chrome瀏覽器。瀏覽器

打開網頁，會提示你是否容許這個網頁應用訪問您的手機攝像頭。點擊容許：服務器

用手機上的攝像頭掃描這張圖片：app

神奇的事情就發生了。您會看到，經過手機攝像頭望過去，手機屏幕裏會出現一個新的不斷滾動的3D物體，以下圖所示。框架

下面具體介紹這個最簡單的例子是怎麼開發出來的。dom

全部的源代碼在個人github上：

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

新建一個html文件，把下列150行代碼粘貼進去，而後在服務器上運行，使用以前描述的步驟便可進行AR測試：

<!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>

固然，這個效果來自大神jeromeetienne開源的AR.js:

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

固然大神本身也很謙虛地提到，他這個開源的加強現實框架也是創建在巨人的肩膀上開發的：好比其中3D效果的繪製，使用到了另外一個開源框架three.js:

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