cesium-examples/VisualTool/Apps/Libs/wind/Windy.js

//define([ 'windy/Particle', 'windy/WindField'], function ( Particle, WindField) {
    var _primitives = null;
    var SPEED_RATE = 0.15;
    var PARTICLES_NUMBER =2000;//默认2000
    var MAX_AGE = 10;
    var BRIGHTEN = 1.5;
    
    var Windy = function (json, cesiumViewer) {
        this.windData = json;
        this.windField = null;
        this.particles = [];
        this.lines = null;
        _primitives = cesiumViewer.scene.primitives;
        this._init();
    };
    Windy.prototype = {
        constructor: Windy,
        _init: function () {
            // 创建风场网格
            this.windField = this.createField();
            // 创建风场粒子
            for (var i = 0; i < PARTICLES_NUMBER; i++) {
                this.particles.push(this.randomParticle(new Particle()));
            }
        },
        createField: function () {
            var data = this._parseWindJson();
            return new WindField(data);
        },
        animate: function () {
            var self = this,
                field = self.windField,
                particles = self.particles;
    
            var instances = [],
                nextX = null,
                nextY = null,
                xy = null,
                uv = null;
            particles.forEach(function (particle) {
                if (particle.age <= 0) {
                    self.randomParticle(particle);
                }
                if (particle.age > 0) {
                    var x = particle.x,
                        y = particle.y;
    
                    if (!field.isInBound(x, y)) {
                        particle.age = 0;
                    } else {
                        uv = field.getIn(x, y);
                        nextX = x +  SPEED_RATE * uv[0];
                        nextY = y +  SPEED_RATE * uv[1];
                        particle.path.push(nextX, nextY);
                        particle.x = nextX;
                        particle.y = nextY;
                        instances.push(self._createLineInstance(self._map(particle.path), particle.age / particle.birthAge));
                        particle.age--;
                    }
                }
            });
            if (instances.length <= 0) this.removeLines();
            self._drawLines(instances);
        },
        _parseWindJson: function () {
            var uComponent = null,
                vComponent = null,
                header = null;
            this.windData.forEach(function (record) {
                var type = record.header.parameterCategory + "," + record.header.parameterNumber;
                switch (type) {
                    case "2,2":
                        uComponent = record['data'];
                        header = record['header'];
                        break;
                    case "2,3":
                        vComponent = record['data'];
                        break;
                    default:
                        break;
                }
            });
            return {
                header: header,
                uComponent: uComponent,
                vComponent: vComponent
            };
        },
        removeLines: function () {
            if (this.lines) {
                _primitives.remove(this.lines);
                this.lines.destroy();
            }
        },
        //求路径上点
        _map: function (arr) {
            var length = arr.length,
                field = this.windField,
                dx = field.dx,
                dy = field.dy,
                west = field.west,
                south = field.north,
                newArr = [];
            for (var i = 0; i <= length - 2; i += 2) {
                newArr.push(
                    west + arr[i] * dx,
                    south - arr[i + 1] * dy
                )
            }
            return newArr;
        },
        _createLineInstance: function (positions, ageRate) {
            var colors = [],
                length = positions.length,
                count = length / 2;
            for (var i = 0; i < length; i++) {
                colors.push(Cesium.Color.WHITE.withAlpha(i / count * ageRate * BRIGHTEN));
            }
            return new Cesium.GeometryInstance({
                geometry: new Cesium.PolylineGeometry({
                    positions: Cesium.Cartesian3.fromDegreesArray(positions),
                    colors: colors,
                    width: 1.5,
                    colorsPerVertex: true
                })
            });
        },
        _drawLines: function (lineInstances) {
            this.removeLines();
            var linePrimitive = new Cesium.Primitive({
                appearance: new Cesium.PolylineColorAppearance({
                    translucent: true
                }),
                geometryInstances: lineInstances,
                asynchronous: false
            });
            this.lines = _primitives.add(linePrimitive);
        },
        randomParticle: function (particle) {
            var safe = 30,x, y;
    
            do {
                x = Math.floor(Math.random() * (this.windField.cols - 2));
                y = Math.floor(Math.random() * (this.windField.rows - 2));
            } while (this.windField.getIn(x, y)[2] <= 0 && safe++ < 30);
    
            particle.x = x;
            particle.y = y;
            particle.age = Math.round(Math.random() * MAX_AGE);//每一次生成都不一样
            particle.birthAge = particle.age;
            particle.path = [x, y];
            return particle;
        }
    };
    
    //return Windy;
    //})