烟雾效果 · Smoke Effect · ▶ 在线运行案例

烟雾效果

你将学到什么

  • Cesium Entity 高层实体 API

效果说明

本案例演示 烟雾效果 效果：基于 WebGL 实现「烟雾效果」可视化效果，附完整可运行源码；核心用到 Cesium。建议先打开文首在线案例查看动态画面，再对照下方源码逐步理解。

核心概念

  • Viewer 聚合 Scene、Camera、Clock 与渲染循环，是 Cesium 应用入口。
  • Entity 面向点线面/模型/标签的高层 API；与 Primitive 相比更适合交互与属性驱动。
  • 阅读下方完整源码时，建议从 init / load / animate 三条主线入手，再深入 shader 与工具函数。

实现步骤

  1. 创建 Viewer，配置地形/影像（若案例需要）并设置初始相机
  2. 在 requestAnimationFrame 循环中更新状态并 render（Cesium 为 viewer.render 或自动渲染）

代码要点

import * as Cesium from 'cesium'

const box = document.getElementById('box')

const viewer = new Cesium.Viewer(box, {

    animation: false,//是否创建动画小器件，左下角仪表    

    baseLayerPicker: false,//是否显示图层选择器，右上角图层选择按钮

    baseLayer: Cesium.ImageryLayer.fromProviderAsync(Cesium.ArcGisMapServerImageryProvider.fromUrl('https://server.arcgisonline.com/arcgis/rest/services/World_Imagery/MapServer')),

    fullscreenButton: false,//是否显示全屏按钮，右下角全屏选择按钮

    timeline: false,//是否显示时间轴    

    infoBox: false,//是否显示信息框   

})

viewer.scene.debugShowFramesPerSecond = true;
viewer.scene.globe.depthTestAgainstTerrain = true;

//喷雾特效
//烟特效
class smokeEffect {
    constructor(viewer, obj) {
        this.viewer = viewer
        this.viewModel = {
            emissionRate: 5,
            gravity: 0.0,//设置重力参数
            minimumParticleLife: 1,
            maximumParticleLife: 6,
            minimumSpeed: 1.0,//粒子发射的最小速度
            maximumSpeed: 4.0,//粒子发射的最大速度
            startScale: 0.0,
            endScale: 10.0,
            particleSize: 25.0,
        }
        this.emitterModelMatrix = new Cesium.Matrix4()
        this.translation = new Cesium.Cartesian3()
        this.rotation = new Cesium.Quaternion()
        this.hpr = new Cesium.HeadingPitchRoll()
        this.trs = new Cesium.TranslationRotationScale()
        this.scene = this.viewer.scene
        this.particleSystem = ''
        this.entity = this.viewer.entities.add({
            //选择粒子放置的坐标
            position: Cesium.Cartesian3.fromDegrees(
                obj.lng, obj.lat, 100
            ),
        });
        this.init();
    }

    init() {
        const _this = this
        this.viewer.clock.shouldAnimate = true;
        this.viewer.scene.globe.depthTestAgainstTerrain = false;
        // this.viewer.trackedEntity = this.entity;
        var particleSystem = this.scene.primitives.add(
            new Cesium.ParticleSystem({
                image: FILE_HOST + "images/channels/cloud.png",//生成所需粒子的图片路径
                //粒子在生命周期开始时的颜色
                startColor: Cesium.Color.BLACK.withAlpha(0.7),
                //粒子在生命周期结束时的颜色
                endColor: Cesium.Color.WHITE.withAlpha(0.3),
                //粒子在生命周期开始时初始比例
                startScale: _this.viewModel.startScale,
                //粒子在生命周期结束时比例
                endScale: _this.viewModel.endScale,
                //粒子发射的最小速度
                minimumParticleLife: _this.viewModel.minimumParticleLife,
                //粒子发射的最大速度
                maximumParticleLife: _this.viewModel.maximumParticleLife,
                //粒子质量的最小界限
                minimumSpeed: _this.viewModel.minimumSpeed,
                //粒子质量的最大界限
                maximumSpeed: _this.viewModel.maximumSpeed,
                //以像素为单位缩放粒子图像尺寸
                imageSize: new Cesium.Cartesian2(
                    _this.viewModel.particleSize,
                    _this.viewModel.particleSize
                ),
                //每秒发射的粒子数
                emissionRate: _this.viewModel.emissionRate,
                //粒子系统发射粒子的时间（秒）
                lifetime: 16.0,
                //设置粒子的大小是否以米或像素为单位
                sizeInMeters: true,
                //系统的粒子发射器
                emitter: new Cesium.CircleEmitter(2.0),//BoxEmitter 盒形发射器，ConeEmitter 锥形发射器，SphereEmitter 球形发射器，CircleEmitter圆形发射器
                //回调函数，实现各种喷泉、烟雾效果
                updateCallback: (p, dt) => {
                    return this.applyGravity(p, dt);
                },
            })
        );
        this.particleSystem = particleSystem;
        this.preUpdateEvent()
    }

    //场景渲染事件
    preUpdateEvent() {
        let _this = this;
        this.viewer.scene.preUpdate.addEventListener(function (scene, time) {
            //发射器地理位置
            _this.particleSystem.modelMatrix = _this.computeModelMatrix(_this.entity, time);
            //发射器局部位置
            _this.particleSystem.emitterModelMatrix = _this.computeEmitterModelMatrix();
            // 将发射器旋转
            if (_this.viewModel.spin) {
                _this.viewModel.heading += 1.0;
                _this.viewModel.pitch += 1.0;
                _this.viewModel.roll += 1.0;
            }
        });
    }

    computeModelMatrix(entity, time) {
        return entity.computeModelMatrix(time, new Cesium.Matrix4());
    }

    computeEmitterModelMatrix() {
        this.hpr = Cesium.HeadingPitchRoll.fromDegrees(0.0, 0.0, 0.0, this.hpr);
        this.trs.translation = Cesium.Cartesian3.fromElements(
            -4.0,
            0.0,
            1.4,
            this.translation
        );
        this.trs.rotation = Cesium.Quaternion.fromHeadingPitchRoll(this.hpr, this.rotation);

        return Cesium.Matrix4.fromTranslationRotationScale(
            this.trs,
            this.emitterModelMatrix
        );
    }

    applyGravity(p, dt) {
        var gravityScratch = new Cesium.Cartesian3()
        var position = p.position
        Cesium.Cartesian3.normalize(position, gravityScratch)
        Cesium.Cartesian3.fromElements(
            20 * dt,
            30 * dt,
            gravityScratch.y * dt,
            gravityScratch
        );
        p.velocity = Cesium.Cartesian3.add(p.velocity, gravityScratch, p.velocity)
    }

    removeEvent() {
        this.viewer.scene.preUpdate.removeEventListener(this.preUpdateEvent, this);
        this.emitterModelMatrix = undefined;
        this.translation = undefined;
        this.rotation = undefined;
        this.hpr = undefined;
        this.trs = undefined;
    }

    //移除粒子特效
    remove() {
        () => { return this.removeEvent() }; //清除事件
        this.viewer.scene.primitives.remove(this.particleSystem); //删除粒子对象
        this.viewer.entities.remove(this.entity); //删除entity
    }

}

new smokeEffect(viewer, {
    lng: -117.16,
    lat: 32.71
})
viewer.camera.setView({
    destination: Cesium.Cartesian3.fromDegrees(-117.16, 32.71, 300.0)
});

完整源码：GitHub

小结