Javascript 帆布鸟密度

我有一个取自“three.js”项目的bird脚本。现在，有一个问题：有这么多的鸟在飞，这已经不现实了。我试着调整了很多选择，但似乎找不到合适的。请注意，我是这段代码中的noob

    var Boid = function() {

        var vector = new THREE.Vector3(),
        _acceleration, _width = 500, _height = 500, _depth = 200, _goal, _neighborhoodRadius = 50,
        _maxSpeed = 4, _maxSteerForce = 0.1, _avoidWalls = false;

        this.position = new THREE.Vector3();
        this.velocity = new THREE.Vector3();
        _acceleration = new THREE.Vector3();

        this.setGoal = function ( target ) {

            _goal = target;

        }

        this.setAvoidWalls = function ( value ) {

            _avoidWalls = value;

        }

        this.setWorldSize = function ( width, height, depth ) {

            _width = width;
            _height = height;vector
            _depth = depth;

        }

        this.run = function ( boids ) {

            if ( _avoidWalls ) {

                vector.set( - _width, this.position.y, this.position.z );
                vector = this.avoid( vector );
                vector.multiplyScalar( 5 );
                _acceleration.addSelf( vector );

                vector.set( _width, this.position.y, this.position.z );
                vector = this.avoid( vector );
                vector.multiplyScalar( 5 );
                _acceleration.addSelf( vector );

                vector.set( this.position.x, - _height, this.position.z );
                vector = this.avoid( vector );
                vector.multiplyScalar( 5 );
                _acceleration.addSelf( vector );

                vector.set( this.position.x, _height, this.position.z );
                vector = this.avoid( vector );
                vector.multiplyScalar( 5 );
                _acceleration.addSelf( vector );

                vector.set( this.position.x, this.position.y, - _depth );
                vector = this.avoid( vector );
                vector.multiplyScalar( 5 );
                _acceleration.addSelf( vector );

                vector.set( this.position.x, this.position.y, _depth );
                vector = this.avoid( vector );
                vector.multiplyScalar( 5 );
                _acceleration.addSelf( vector );

            }/* else {

                this.checkBounds();

            }
            */

            if ( Math.random() > 0.5 ) {

                this.flock( boids );

            }

            this.move();

        }

        this.flock = function ( boids ) {

            if ( _goal ) {

                _acceleration.addSelf( this.reach( _goal, 0.005 ) );

            }

            _acceleration.addSelf( this.alignment( boids ) );
            _acceleration.addSelf( this.cohesion( boids ) );
            _acceleration.addSelf( this.separation( boids ) );

        }

        this.move = function () {

            this.velocity.addSelf( _acceleration );

            var l = this.velocity.length();

            if ( l > _maxSpeed ) {

                this.velocity.divideScalar( l / _maxSpeed );

            }

            this.position.addSelf( this.velocity );
            _acceleration.set( 0, 0, 0 );

        }

        this.checkBounds = function () {

            if ( this.position.x >   _width ) this.position.x = - _width;
            if ( this.position.x < - _width ) this.position.x =   _width;
            if ( this.position.y >   _height ) this.position.y = - _height;
            if ( this.position.y < - _height ) this.position.y =  _height;
            if ( this.position.z >  _depth ) this.position.z = - _depth;
            if ( this.position.z < - _depth ) this.position.z =  _depth;

        }

        //

        this.avoid = function ( target ) {

            var steer = new THREE.Vector3();

            steer.copy( this.position );
            steer.subSelf( target );

            steer.multiplyScalar( 1 / this.position.distanceToSquared( target ) );

            return steer;

        }

        this.repulse = function ( target ) {

            var distance = this.position.distanceTo( target );

            if ( distance < 150 ) {

                var steer = new THREE.Vector3();

                steer.sub( this.position, target );
                steer.multiplyScalar( 0.5 / distance );

                _acceleration.addSelf( steer );

            }

        }

        this.reach = function ( target, amount ) {

            var steer = new THREE.Vector3();

            steer.sub( target, this.position );
            steer.multiplyScalar( amount );

            return steer;

        }

        this.alignment = function ( boids ) {

            var boid, velSum = new THREE.Vector3(),
            count = 0;

            for ( var i = 0, il = boids.length; i < il; i++ ) {

                if ( Math.random() > 0.6 ) continue;

                boid = boids[ i ];

                distance = boid.position.distanceTo( this.position );

                if ( distance > 0 && distance <= _neighborhoodRadius ) {

                    velSum.addSelf( boid.velocity );
                    count++;

                }

            }

            if ( count > 0 ) {

                velSum.divideScalar( count );

                var l = velSum.length();

                if ( l > _maxSteerForce ) {

                    velSum.divideScalar( l / _maxSteerForce );

                }

            }

            return velSum;

        }

        this.cohesion = function ( boids ) {

            var boid, distance,
            posSum = new THREE.Vector3(),
            steer = new THREE.Vector3(),
            count = 0;

            for ( var i = 0, il = boids.length; i < il; i ++ ) {

                if ( Math.random() > 0.6 ) continue;

                boid = boids[ i ];
                distance = boid.position.distanceTo( this.position );

                if ( distance > 0 && distance <= _neighborhoodRadius ) {

                    posSum.addSelf( boid.position );
                    count++;

                }

            }

            if ( count > 0 ) {

                posSum.divideScalar( count );

            }

            steer.sub( posSum, this.position );

            var l = steer.length();

            if ( l > _maxSteerForce ) {

                steer.divideScalar( l / _maxSteerForce );

            }

            return steer;

        }

        this.separation = function ( boids ) {

            var boid, distance,
            posSum = new THREE.Vector3(),
            repulse = new THREE.Vector3();

            for ( var i = 0, il = boids.length; i < il; i ++ ) {

                if ( Math.random() > 0.6 ) continue;

                boid = boids[ i ];
                distance = boid.position.distanceTo( this.position );

                if ( distance > 0 && distance <= _neighborhoodRadius ) {

                    repulse.sub( this.position, boid.position );
                    repulse.normalize();
                    repulse.divideScalar( distance );
                    posSum.addSelf( repulse );

                }

            }

            return posSum;

        }

    }

</script>

<script>

    var SCREEN_WIDTH = window.innerWidth,
    SCREEN_HEIGHT = window.innerHeight,
    SCREEN_WIDTH_HALF = SCREEN_WIDTH  / 2,
    SCREEN_HEIGHT_HALF = SCREEN_HEIGHT / 2;

    var camera, scene, renderer,
    birds, bird;

    var boid, boids;

    init();
    animate();

    function init() {

        camera = new THREE.PerspectiveCamera( 75, SCREEN_WIDTH / SCREEN_HEIGHT, 1, 10000 );
        camera.position.z = 450;

        scene = new THREE.Scene();

        birds = [];
        boids = [];

        for ( var i = 0; i < 200; i ++ ) {

            boid = boids[ i ] = new Boid();
            boid.position.x = Math.random() * 400 - 200;
            boid.position.y = Math.random() * 400 - 200;
            boid.position.z = Math.random() * 400 - 200;
            boid.velocity.x = Math.random() * 2 - 1;
            boid.velocity.y = Math.random() * 2 - 1;
            boid.velocity.z = Math.random() * 2 - 1;
            boid.setAvoidWalls( true );
            boid.setWorldSize( 500, 500, 400 );

            bird = birds[ i ] = new THREE.Mesh( new Bird(), new THREE.MeshBasicMaterial( { color:Math.random() * 0xffffff, side: THREE.DoubleSide } ) );
            bird.phase = Math.floor( Math.random() * 62.83 );
            bird.position = boids[ i ].position;
            scene.add( bird );


        }

        renderer = new THREE.CanvasRenderer();
        // renderer.autoClear = false;
        renderer.setSize( SCREEN_WIDTH, SCREEN_HEIGHT );

        document.addEventListener( 'mousemove', onDocumentMouseMove, false );
        document.body.appendChild( renderer.domElement );

        //

        window.addEventListener( 'resize', onWindowResize, false );

    }

    function onWindowResize() {

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

        renderer.setSize( window.innerWidth, window.innerHeight );

    }

    function onDocumentMouseMove( event ) {

        var vector = new THREE.Vector3( event.clientX - SCREEN_WIDTH_HALF, - event.clientY + SCREEN_HEIGHT_HALF, 0 );

        for ( var i = 0, il = boids.length; i < il; i++ ) {

            boid = boids[ i ];

            vector.z = boid.position.z;

            boid.repulse( vector );

        }

    }

    //

    function animate() {

        requestAnimationFrame( animate );

        render();
        stats.update();

    }

    function render() {

        for ( var i = 0, il = birds.length; i < il; i++ ) {

            boid = boids[ i ];
            boid.run( boids );

            bird = birds[ i ];

            color = bird.material.color;
            color.r = color.g = color.b = ( 500 - bird.position.z ) / 1000;

            bird.rotation.y = Math.atan2( - boid.velocity.z, boid.velocity.x );
            bird.rotation.z = Math.asin( boid.velocity.y / boid.velocity.length() );

            bird.phase = ( bird.phase + ( Math.max( 0, bird.rotation.z ) + 0.1 )  ) % 62.83;
            bird.geometry.vertices[ 5 ].y = bird.geometry.vertices[ 4 ].y = Math.sin( bird.phase ) * 5;

        }

        renderer.render( scene, camera );

    }

var Boid=function（）{
var vector=new THREE.Vector3（），
_加速度，_宽度=500，_高度=500，_深度=200，_目标，_邻里半径=50，
_maxSpeed=4，_maxSteerForce=0.1，_avoidWalls=false；
this.position=新的3.Vector3（）；
this.velocity=新的3.Vector3（）；
_加速度=新的3.Vector3（）；
this.setGoal=函数（目标）{
_目标=目标；
}
this.setAvoidWalls=函数（值）{
_避免墙=价值；
}
this.setWorldSize=函数（宽度、高度、深度）{
_宽度=宽度；
_高度=高度；向量
_深度=深度；
}
this.run=函数（boids）{
如果（避免墙壁）{
向量集（-u宽度，此位置.y，此位置.z）；
向量=这个。避免（向量）；
向量多重标度（5）；
_加速度。addSelf（向量）；
向量集（_width，this.position.y，this.position.z）；
向量=这个。避免（向量）；
向量多重标度（5）；
_加速度。addSelf（向量）；
vector.set（此位置.x，-u高度，此位置.z）；
向量=这个。避免（向量）；
向量多重标度（5）；
_加速度。addSelf（向量）；
vector.set（this.position.x，_height，this.position.z）；
向量=这个。避免（向量）；
向量多重标度（5）；
_加速度。addSelf（向量）；
vector.set（此.position.x，此.position.y，--u深度）；
向量=这个。避免（向量）；
向量多重标度（5）；
_加速度。addSelf（向量）；
vector.set（this.position.x，this.position.y，_深度）；
向量=这个。避免（向量）；
向量多重标度（5）；
_加速度。addSelf（向量）；
}/*否则{
this.checkBounds（）；
}
*/
if（Math.random（）>0.5）{
这是羊群；
}
这个。移动（）；
}
this.flock=函数（boids）{
如果（_目标）{
_加速.addSelf（这个.reach（_目标，0.005））；
}
_加速度.addSelf（this.alignment（boids））；
_acceleration.addSelf（this.ne聚力（boids））；
_加速度.addSelf（this.separation（boids））；
}
this.move=函数（）{
这个.velocity.addSelf（_加速度）；
var l=这个.velocity.length（）；
如果（l>\u最大速度）{
此.velocity.divideScalar（l/_maxSpeed）；
}
this.position.addSelf（this.velocity）；
_加速度设置（0,0,0）；
}
this.checkBounds=函数（）{
如果（this.position.x>\u width）this.position.x=-\u width；
如果（this.position.x<-\u width）this.position.x=\u width；
如果（this.position.y>\u height）this.position.y=-\u height；
如果（this.position.y<-\u高度）this.position.y=\u高度；
如果（this.position.z>_depth）this.position.z=-_depth；
如果（this.position.z<-\u depth）this.position.z=\u depth；
}
//
this.avoid=函数（目标）{
var steer=new THREE.Vector3（）；
转向。复制（此位置）；
转向。自底（目标）；
转向多刻度（1/此位置距离方形（目标））；
返回转向；
}
this.shuffer=函数（目标）{
var距离=此.position.distanceTo（目标）；
如果（距离<150）{
var steer=new THREE.Vector3（）；
转向接头（该位置、目标）；
转向倍率标度（0.5/距离）；
_加速。添加自我（转向）；
}
}
this.reach=功能（目标、金额）{
var steer=new THREE.Vector3（）；
转向接头（目标，本位置）；
转向倍数标度（数量）；
返回转向；
}
this.alignment=函数（boids）{
var boid，velSum=new THREE.Vector3（），
计数=0；
对于（var i=0，il=boids.length；i0.6）继续；
boid=boid[i]；
距离=锅炉位置距离（此位置）；
如果（距离>0&&距离0）{
velSum.divideScalar（计数）；
var l=velSum.length（）；
如果（l>\u maxSteerForce）{
velSum.divideScalar（l/_maxSteerForce）；
}
}
返回velSum；
}
this.ne聚力=函数（boids）{
var boid，距离，
posSum=new-THREE.Vector3（），
转向=新的三个。矢量3（），
计数=0；
对于（var i=0，il=boids.length；i0.6）继续；
boid=boid[i]；
距离=锅炉位置距离（此位置）；
如果（距离>0&&距离0）{
分保（计数）；
}
转向接头（负鼠，此位置）；
var l=转向长度（）；
如果（l>\u maxSteerForce）{
steer.divideScalar（l/_最大值
for ( var i = 0; i < 200; i ++ ) { <-- reduce the 200