html5的canvas实现3d雪花飘舞效果

var SCREEN_WIDTH = window.innerWidth;
var SCREEN_HEIGHT = window.innerHeight;

var container;

var particle;

var camera;
var scene;
var renderer;

var mouseX = 0;
var mouseY = 0;

var windowHalfX = window.innerWidth / 2;
var windowHalfY = window.innerHeight / 2;

var particles = [];
var particleImage = new Image();//THREE.ImageUtils.loadTexture( "img/ParticleSmoke.png-600" );
particleImage.src = 'images/ParticleSmoke.png-600';

function init() {

container = document.createElement('div');
document.body.appendChild(container);

camera = new THREE.PerspectiveCamera( 75, SCREEN_WIDTH / SCREEN_HEIGHT, 1, 10000 );
camera.position.z = 1000;

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++) {

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);
}

container.appendChild( renderer.domElement );

document.addEventListener( 'mousemove', onDocumentMouseMove, false );
document.addEventListener( 'touchstart', onDocumentTouchStart, false );
document.addEventListener( 'touchmove', onDocumentTouchMove, false );

setInterval( loop, 1000 / 60 );

}

function onDocumentMouseMove( event ) {

mouseX = event.clientX - windowHalfX;
mouseY = event.clientY - windowHalfY;
}

function onDocumentTouchStart( event ) {

if ( event.touches.length == 1 ) {

event.preventDefault();

mouseX = event.touches[ 0 ].pageX - windowHalfX;
mouseY = event.touches[ 0 ].pageY - windowHalfY;
}
}

function onDocumentTouchMove( event ) {

if ( event.touches.length == 1 ) {

event.preventDefault();

mouseX = event.touches[ 0 ].pageX - windowHalfX;
mouseY = event.touches[ 0 ].pageY - windowHalfY;
}
}

//

function loop() {

for(var i = 0; i {

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);

renderer.render( scene, camera );

}