html5中怎么利用canvas实现3d雪花飘舞效果

html5中怎么利用canvas实现3d雪花飘舞效果，很多新手对此不是很清楚，为了帮助大家解决这个难题，下面小编将为大家详细讲解，有这方面需求的人可以来学习下，希望你能有所收获。

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.class="lazy" data-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>    
  }

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