html5的canvas实现3d雪花飘舞效果

var SCREEN_WIDTH = window.innerWidth;
   var SCREEN_HEIGHT = window.innerHeight;</p>
<p>   var container;</p>
<p>   var particle;</p>
<p>   var camera;
   var scene;
   var renderer;</p>
<p>   var mouseX = 0;
   var mouseY = 0;</p>
<p>   var windowHalfX = window.innerWidth / 2;
   var windowHalfY = window.innerHeight / 2;
   
   var particles = []; 
   var particleImage = new Image();//THREE.ImageUtils.loadTexture( "img/ParticleSmoke.png" );
   particleImage.src = 'images/ParticleSmoke.png'; </p>
<p>  
  
   function init() {</p>
<p>    container = document.createElement('div');
    document.body.appendChild(container);</p>
<p>    camera = new THREE.PerspectiveCamera( 75, SCREEN_WIDTH / SCREEN_HEIGHT, 1, 10000 );
    camera.position.z = 1000;</p>
<p>    scene = new THREE.Scene();
    scene.add(camera);
     
    renderer = new THREE.CanvasRenderer();
    renderer.setSize(SCREEN_WIDTH, SCREEN_HEIGHT);
    var material = new THREE.ParticleBasicMaterial( { map: new THREE.Texture(particleImage) } );
     
    for (var i = 0; i < 500; i++) {</p>
<p>     particle = new Particle3D( material);
     particle.position.x = Math.random() * 2000 - 1000;
     particle.position.y = Math.random() * 2000 - 1000;
     particle.position.z = Math.random() * 2000 - 1000;
     particle.scale.x = particle.scale.y =  1;
     scene.add( particle );
     
     particles.push(particle); 
    }</p>
<p>    container.appendChild( renderer.domElement );</p>
<p> 
    document.addEventListener( 'mousemove', onDocumentMouseMove, false );
    document.addEventListener( 'touchstart', onDocumentTouchStart, false );
    document.addEventListener( 'touchmove', onDocumentTouchMove, false );
    
    setInterval( loop, 1000 / 60 );
    
   }
   
   function onDocumentMouseMove( event ) {</p>
<p>    mouseX = event.clientX - windowHalfX;
    mouseY = event.clientY - windowHalfY;
   }</p>
<p>   function onDocumentTouchStart( event ) {</p>
<p>    if ( event.touches.length == 1 ) {</p>
<p>     event.preventDefault();</p>
<p>     mouseX = event.touches[ 0 ].pageX - windowHalfX;
     mouseY = event.touches[ 0 ].pageY - windowHalfY;
    }
   }</p>
<p>   function onDocumentTouchMove( event ) {</p>
<p>    if ( event.touches.length == 1 ) {</p>
<p>     event.preventDefault();</p>
<p>     mouseX = event.touches[ 0 ].pageX - windowHalfX;
     mouseY = event.touches[ 0 ].pageY - windowHalfY;
    }
   }</p>
<p>   //</p>
<p>   function loop() {</p>
<p>   for(var i = 0; i<particles.length; i++)
    {</p>
<p>     var particle = particles[i]; 
     particle.updatePhysics(); 
 
     with(particle.position)
     {
      if(y<-1000) y+=2000; 
      if(x>1000) x-=2000; 
      else if(x<-1000) x+=2000; 
      if(z>1000) z-=2000; 
      else if(z<-1000) z+=2000; 
     }    
    }
   
    camera.position.x += ( mouseX - camera.position.x ) * 0.05;
    camera.position.y += ( - mouseY - camera.position.y ) * 0.05;
    camera.lookAt(scene.position); </p>
<p>    renderer.render( scene, camera );</p>
<p>    
   }