ThreeJS学习笔记(四)——粒子系统

粒子和粒子系统

Threejs中制作粒子效果有两种方法：

• THREE.Particle和THREE.ParticleSytem
  如果项目使用的渲染器是CanvasRenderer,直接使用THREE.Particle创建完粒子即可直接添加到scene中，但是如果使用的是WebGlRenderer渲染器，那就要先创建THREE.ParticleSytem对象，然后通过这个对象来创建粒子。PatricleSystem具有形体和材质两个属性，因此使用PatitlceSystem可以借助几何体生成粒子，也可以先创建一个由多个点构成的形体后去创建粒子。

• THREE.Sprite
  使用Sprite来制作粒子可以实现以下两种需求：
  1.使用useScreenCoordinates:true属性建立一个独立于camera摄像范围之外的元素，即它在屏幕上的位置不受camera的位置和焦点变化而变化，它的移动、定位、缩放是基于屏幕坐标的。
  2.与在CanvasRenderer渲染器中使用THREE.Particle创建粒子一样，不需要使用THREE.ParticleSytem， 在WebGlRenderer渲染器中使用THREE.Sprite创建的粒子可以直接添加到scene中。三维场景中创建出来的精灵总是面向镜头的。即不会有倾斜变形之类透视变化，只有近大远小的变化

THREE.Sprite

• Sprite默认大小是1*1,设置Sprite大小需要使用scale进行缩放
• Sprite的样式通过参数meterial定义，参数meterial是使用THREE.SpriteMaterial类创建的材质对象
• THREE.SpriteMaterial可以定义精灵的颜色和纹理，纹理对象可以调用new THREE.ImgesUtils.loadTexture(url)来引用一张图片作为纹理，也可以调用new THREE.CanvasTexture( canvas)，使用动态绘制的canvas图作为纹理。

创建粒子

以下创建了300个粒子，并添加到场景中，

function createCanvas(width,height,colors){//创建画布并绘制精灵纹理
    var canvas = document.createElement( 'canvas' );
    canvas.width = width;
    canvas.height = height;
    var context = canvas.getContext( '2d' );
    var gradient = context.createRadialGradient( canvas.width / 2, canvas.height / 2, 0, canvas.width / 2, canvas.height / 2, canvas.width / 2 );
    colors.forEach(function(color){
        gradient.addColorStop( color.start, color.rgba );
    })
    context.fillStyle = gradient;
    context.fillRect( 0, 0, canvas.width, canvas.height );
    return canvas;
}
function createMaterial(width,height,colors){//使用画布创建材质
    var sprite=createCanvas(width,height,colors);
    return new THREE.SpriteMaterial( {
        map: new THREE.CanvasTexture( sprite ),
        blending: THREE.AdditiveBlending,//使用饱和度叠加的混和模式渲染粒子
        overdraw:false,
        depthWrite:false
    } )
}
function initParticle( particle,coord,size) {//初始化粒子
    var particle = this instanceof THREE.Sprite ? this : particle;
    if(!size&&size!=0){
        size=Math.random() * 32 + 16;
    }
    particle.scale.x = particle.scale.y = size;
    particle.position.set( coord.x,coord.y,coord.z);    
}
function addParticles(){//在场景中创建300个粒子，粒子颜色在一个范围内随机取色
    for ( var i = 0; i < 300; i++ ) {
        var deepColor=Math.round(Math.random()*255);
        var lightColor=Math.round(deepColor*32/255);
        var material= createMaterial(32,32,[
            {start:0,rgba:'rgba(255,255,255,1)'},
            {start:0.2,rgba:'rgba(0,'+deepColor+','+Math.round(Math.random()*80+175)+',1)'},
            {start:0.4,rgba:'rgba(0,'+lightColor+',64,1)'},
            {start:1,rgba:'rgba(0,0,0,1)'}
        ])
        var particle = new THREE.Sprite(material);
        initParticle(particle, new THREE.Vector3(Math.random()*500-250,Math.random()*500-250,Math.random()*500-250),10);
        scene.add( particle );
    }
}

            

执行addParticles()后如图所示

粒子的运动

粒子的缓运动画也都是用上一节说到的Tween.js实现的。循环动画示例如下：

function addParticles(){//在场景中创建300个粒子，粒子颜色在一个范围内随机取色
            for ( var i = 0; i < 300; i++ ) {
                var deepColor=Math.round(Math.random()*255);
                var lightColor=Math.round(deepColor*32/255);
                var material= createMaterial(32,32,[
                    {start:0,rgba:'rgba(255,255,255,1)'},
                    {start:0.2,rgba:'rgba(0,'+deepColor+','+Math.round(Math.random()*80+175)+',1)'},
                    {start:0.4,rgba:'rgba(0,'+lightColor+',64,1)'},
                    {start:1,rgba:'rgba(0,0,0,1)'}
                ])
                var particle = new THREE.Sprite(material);
                _particles.push(particle);
                //initParticle(particle, new THREE.Vector3(Math.random()*500-250,Math.random()*500-250,Math.random()*500-250),10)
                var delay=i*5;
                particleLoop(particle,delay)
                scene.add( particle );
            }
        }
        function initParticle( particle,coord,size) {
            var particle = this instanceof THREE.Sprite ? this : particle;
            if(!size&&size!=0){
                size=Math.random() * 32 + 16;
            }
            particle.scale.x = particle.scale.y = size;
            particle.position.set( coord.x,coord.y,coord.z);    
        }
        
        function particleLoop(particle,delay){
            particle=particle?particle:this;
            initParticle(particle,new THREE.Vector3(Math.random()*500-250,Math.random()*500-250,Math.random()*500-250),Math.random() * 12 + 8);
            delay=delay?delay:0;
            new TWEEN.Tween( particle )
                .delay( delay )
                .to( {}, 1500 )
                .onComplete(particleLoop )
                .start();
            new TWEEN.Tween( particle.position )
                .delay( delay )
                .to( { x:0, y: 0, z: 0}, 1500 )
                .start();
            new TWEEN.Tween( particle.scale )
                .delay( delay )
                .to( { x: 8, y: 8 }, 1500 )
                .start();
        }

本章示例

<!DOCTYPE html>
<html>
    <head>
        <meta charset="UTF-8">
        <title></title>
    </head>
    <body>
    <div id="space"></div>  
    <script   src="https://code.jquery.com/jquery-1.12.4.min.js"   integrity="sha256-ZosEbRLbNQzLpnKIkEdrPv7lOy9C27hHQ+Xp8a4MxAQ="   crossorigin="anonymous"></script>
    <script src="../js/lib/threejs/three.js"></script>
    
    <script src="../js/lib/threejs/OrbitControls.js"></script>
    <script src="../js/lib/Tween.js"></script>
    <script>
        

            var container, stats; 

            var camera, scene, renderer,_particles=[];

            var mouseX = 0, mouseY = 0;

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


            init();
            animate();
            var mesh;

            function init() {

                container = document.getElementById("space")
                camera = new THREE.PerspectiveCamera( 45, window.innerWidth / window.innerHeight, 1, 5000 );
                camera.position.set(0, 0, 1500);
                
                scene = new THREE.Scene();

                var ambient = new THREE.AmbientLight( 0xffffff );
                scene.add( ambient );
                
                
                var directionalLight = new THREE.DirectionalLight( 0xffffff );
                directionalLight.position.set( -5, 5, 5).normalize();
                scene.add( directionalLight );

                var pointlight = new THREE.PointLight(0x63d5ff, 1, 200); 
                pointlight.position.set(0, 0, 200);
                scene.add( pointlight );                
                var pointlight2 = new THREE.PointLight(0xffffff, 1, 200); 
                pointlight2.position.set(-200, 200, 200);
                scene.add( pointlight2 );
                var pointlight3 = new THREE.PointLight(0xffffff, 1.5, 200); 
                pointlight3.position.set(-200, 200, 0);
                scene.add( pointlight3 );

                var controls = new THREE.OrbitControls(camera,container);
            //controls.maxPolarAngle=1.5;
            //controls.minPolarAngle=1;
            controls.enableDamping=true;
            controls.enableKeys=false;
            controls.enablePan=false;
            controls.dampingFactor = 0.1;
            controls.rotateSpeed=0.1;
    //      controls.enabled = false;
            //controls.minDistance=1000;
            //controls.maxDistance=3000;
                
                
                
                var path = "../resource/sky";
                var format = '.jpg';
                var urls = [
                        path + 'px' + format, path + 'nx' + format,
                        path + 'py' + format, path + 'ny' + format,
                        path + 'pz' + format, path + 'nz' + format
                    ];
                var skyMaterials = []; 
                for (var i = 0; i < urls.length; ++i) {
                    var loader = new THREE.TextureLoader();
                    loader.setCrossOrigin( this.crossOrigin );
                    var texture = loader.load( urls[i], function(){}, undefined, function(){} );
                    
                    skyMaterials.push(new THREE.MeshBasicMaterial({
                        //map: THREE.ImageUtils.loadTexture(urls[i], {},function() { }), 
                        map: texture, 
                        overdraw: true,
                        side: THREE.BackSide,
                        //transparent: true,
                        //needsUpdate:true,
                        premultipliedAlpha: true
                        //depthWrite:true,
                        
        //              wireframe:false,
                    })
                    ); 
                    
                } 
                
                var cube = new THREE.Mesh(new THREE.CubeGeometry(500, 500,500), new THREE.MeshFaceMaterial(skyMaterials)); 
                cube.name="sky";
                //scene.add(cube);
                addParticles();
                
                renderer = new THREE.WebGLRenderer();
                renderer.setPixelRatio( window.devicePixelRatio );
                renderer.setSize( window.innerWidth, window.innerHeight );
                container.appendChild( renderer.domElement );

                document.addEventListener( 'mousemove', onDocumentMouseMove, false );
                window.addEventListener( 'resize', onWindowResize, false );

            }
            function createCanvas(width,height,colors){//创建画布并绘制精灵纹理
                var canvas = document.createElement( 'canvas' );
                canvas.width = width;
                canvas.height = height;
                var context = canvas.getContext( '2d' );
                var gradient = context.createRadialGradient( canvas.width / 2, canvas.height / 2, 0, canvas.width / 2, canvas.height / 2, canvas.width / 2 );
                colors.forEach(function(color){
                    gradient.addColorStop( color.start, color.rgba );
                })
                context.fillStyle = gradient;
                context.fillRect( 0, 0, canvas.width, canvas.height );
                return canvas;
            }
            function createMaterial(width,height,colors){//使用画布创建材质
                var sprite=createCanvas(width,height,colors);
                return new THREE.SpriteMaterial( {
                    map: new THREE.CanvasTexture( sprite ),
                    blending: THREE.AdditiveBlending,
                    overdraw:false,
                    depthWrite:false
                } )
             }
            function addParticles(){//在场景中创建300个粒子，粒子颜色在一个范围内随机取色
                for ( var i = 0; i < 300; i++ ) {
                    var deepColor=Math.round(Math.random()*255);
                    var lightColor=Math.round(deepColor*32/255);
                    var material= createMaterial(32,32,[
                        {start:0,rgba:'rgba(255,255,255,1)'},
                        {start:0.2,rgba:'rgba(0,'+deepColor+','+Math.round(Math.random()*80+175)+',1)'},
                        {start:0.4,rgba:'rgba(0,'+lightColor+',64,1)'},
                        {start:1,rgba:'rgba(0,0,0,1)'}
                    ])
                    var particle = new THREE.Sprite(material);
                    _particles.push(particle);
                    //initParticle(particle, new THREE.Vector3(Math.random()*500-250,Math.random()*500-250,Math.random()*500-250),10)
                    var delay=i*5;
                    particleLoop(particle,delay)
                    scene.add( particle );
                }
            }
            function initParticle( particle,coord,size) {
                var particle = this instanceof THREE.Sprite ? this : particle;
                if(!size&&size!=0){
                    size=Math.random() * 32 + 16;
                }
                particle.scale.x = particle.scale.y = size;
                particle.position.set( coord.x,coord.y,coord.z);    
            }
            
            function particleLoop(particle,delay){
                particle=particle?particle:this;
                initParticle(particle,new THREE.Vector3(Math.random()*500-250,Math.random()*500-250,Math.random()*500-250),Math.random() * 12 + 8);
                delay=delay?delay:0;
                new TWEEN.Tween( particle )
                    .delay( delay )
                    .to( {}, 1500 )
                    .onComplete(particleLoop).onStart(function(){
                        
                    })
                    .start();
                new TWEEN.Tween( particle.position )
                    .delay( delay )
                    .to( { x:0, y: 0, z: 0}, 1500 )
                    .start();
                    
                new TWEEN.Tween( particle.scale )
                    .delay( delay )
                    .to( { x: 8, y: 8 }, 1500 )
                    .start();

            }
            function onWindowResize() {

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

                camera.aspect = window.innerWidth / window.innerHeight;
                camera.updateProjectionMatrix();
                renderer.setSize( window.innerWidth, window.innerHeight );

            }

            function onDocumentMouseMove( event ) {

                mouseX = ( event.clientX - windowHalfX ) / 2;
                mouseY = ( event.clientY - windowHalfY ) / 2;

            }

            //

            function animate() {

                requestAnimationFrame( animate );
                render();
                TWEEN.update();
            }

            function render() {
                
//              camera.position.x += ( mouseX - camera.position.x ) ;
//              camera.position.y += ( mouseY - camera.position.y ) ;

//              for(var i=0,len=_particles.length; i<len; i++){
//                  var posx=(Math.random()-0.5)*1;
//                  var posy=(Math.random()-0.5)*1;
//                  var posz=(Math.random()-0.5)*1;
//                  _particles[i].position.set(_particles[i].position.x+posx,_particles[i].position.y+posy,_particles[i].position.z+posz)
//              }
                camera.lookAt( scene.position );

                renderer.render( scene, camera );

            }

    </script>
    </body>
</html>

来源：http://feg.netease.com/archives/403.html