Particle Explosion

<!--
  示例：用 burst 做周期性爆散
  要点：emissionRate 归零，靠 ParticleBurst 在指定时间一次性抛出大量粒子
  依赖：CesiumJS 1.121 · jsDelivr CDN，火星贴图由 canvas 生成
-->
<!DOCTYPE html>
<html lang="zh-CN">
<head>
<meta name="robots" content="noindex,follow">
<meta charset="utf-8">
<meta name="viewport" content="width=device-width, initial-scale=1">
<title>爆炸粒子</title>
<link rel="stylesheet" href="https://cdn.jsdelivr.net/npm/cesium@1.121.0/Build/Cesium/Widgets/widgets.css">
<style>
  html,body{height:100%;margin:0}
  body{background:#0e1116;color:#e6e8ec;overflow:hidden;
       font:13px/1.6 -apple-system,"Segoe UI","PingFang SC",sans-serif}
  #c{height:100%}
  .hud{position:absolute;left:12px;top:12px;z-index:5;background:rgba(23,28,35,.92);
       border:1px solid #2a313b;border-radius:6px;padding:9px 12px;font-size:12px;
       color:#a2a9b6;width:252px}
  .hud b{color:#e6e8ec;font-weight:600}
  .hud .row{margin-top:7px}
  .hud button{font:inherit;font-size:12px;padding:3px 9px;border-radius:4px;cursor:pointer;
       border:1px solid #343b46;background:#1d232b;color:#cfd6e2;margin-top:8px}
  .cesium-viewer-bottom .cesium-widget-credits,.cesium-viewer-animationContainer,
  .cesium-viewer-timelineContainer{display:none!important}
</style>
</head>
<body>
<div id="c"></div>
<div class="hud">
  <div><b>爆散</b></div>
  <div class="row">每 2.5 秒一组，单组最多 240 粒</div>
  <div class="row">重力让火星落回地面</div>
  <div class="row"><button id="once">清空现有火星</button></div>
</div>
<script src="https://cdn.jsdelivr.net/npm/cesium@1.121.0/Build/Cesium/Cesium.js"></script>
<script>
(function () {
  'use strict';

  var viewer = new Cesium.Viewer('c', {
    baseLayer: false,
    baseLayerPicker: false, geocoder: false, homeButton: false,
    sceneModePicker: false, navigationHelpButton: false,
    animation: false, timeline: false, fullscreenButton: false,
    infoBox: false, selectionIndicator: false
  });

  var scene = viewer.scene;
  scene.globe.baseColor = Cesium.Color.fromCssColorString('#1c2733');
  scene.backgroundColor = Cesium.Color.fromCssColorString('#0e1116');
  scene.skyBox.show = false;
  scene.sun.show = false;
  scene.moon.show = false;
  if (scene.skyAtmosphere) scene.skyAtmosphere.show = false;

  /* 火星贴图：小白点带柔边 */
  function sparkTexture() {
    var c = document.createElement('canvas');
    c.width = c.height = 32;
    var ctx = c.getContext('2d');
    var g = ctx.createRadialGradient(16, 16, 0, 16, 16, 16);
    g.addColorStop(0, 'rgba(255,255,255,1)');
    g.addColorStop(0.45, 'rgba(255,240,190,0.9)');
    g.addColorStop(1, 'rgba(255,200,120,0)');
    ctx.fillStyle = g;
    ctx.fillRect(0, 0, 32, 32);
    return c;
  }

  var TEX = sparkTexture();

  /* 重力 + 阻力，方向都在局部坐标系里 */
  function gravity(particle, dt) {
    particle.velocity.z -= 42 * dt;
    particle.velocity.x *= 0.985;
    particle.velocity.y *= 0.985;
    particle.velocity.z *= 0.995;
  }

  function makeSystem(lng, lat) {
    var matrix = Cesium.Transforms.eastNorthUpToFixedFrame(
      Cesium.Cartesian3.fromDegrees(lng, lat, 240)
    );

    return new Cesium.ParticleSystem({
      image: TEX,
      startColor: Cesium.Color.fromCssColorString('#fff6cf').withAlpha(1),
      endColor: Cesium.Color.fromCssColorString('#ff4d22').withAlpha(0.0),
      startScale: 1.0,
      endScale: 0.5,
      minimumParticleLife: 1.1,
      maximumParticleLife: 2.0,
      minimumSpeed: 45,
      maximumSpeed: 150,
      imageSize: new Cesium.Cartesian2(14, 14),
      emissionRate: 0,
      emitter: new Cesium.SphereEmitter(2.0),
      modelMatrix: matrix,
      lifetime: 5.0,
      loop: true,
      bursts: [
        new Cesium.ParticleBurst({ time: 0.2, minimum: 160, maximum: 240 }),
        new Cesium.ParticleBurst({ time: 2.7, minimum: 160, maximum: 240 })
      ],
      updateCallback: gravity
    });
  }

  var systems = [];
  [[116.382, 39.902], [116.397, 39.902]].forEach(function (p) {
    var s = makeSystem(p[0], p[1]);
    systems.push(s);
    scene.primitives.add(s);
  });

  /* 爆点下的圆台标记 */
  [[116.382, 39.902], [116.397, 39.902]].forEach(function (p) {
    viewer.entities.add({
      position: Cesium.Cartesian3.fromDegrees(p[0], p[1], 20),
      cylinder: {
        length: 40, topRadius: 26, bottomRadius: 34,
        material: Cesium.Color.fromCssColorString('#3a2a24')
      }
    });
  });

  /* 清空已抛出的火星，等下一组 burst 重新开始 */
  document.getElementById('once').addEventListener('click', function () {
    systems.forEach(function (s) {
      if (typeof s.removeAllParticles === 'function') s.removeAllParticles();
    });
  });

  viewer.camera.flyTo({
    destination: Cesium.Cartesian3.fromDegrees(116.376, 39.892, 900),
    orientation: {
      heading: Cesium.Math.toRadians(10),
      pitch: Cesium.Math.toRadians(-12),
      roll: 0
    },
    duration: 0
  });
})();
</script>
</body>
</html>