html5的canvas如何实现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>
}