3D Tiles Interactivity

<!--
  示例：拖动建筑改变位置
  说明：九栋建筑可拖动，选中时描边变黄，拖动时贴地移动
  核心逻辑：LEFT_DOWN 拾取 → MOUSE_MOVE 用 pickEllipsoid 求经纬度 → 改 entity.position → LEFT_UP 复位
  依赖：CesiumJS 1.121 · jsDelivr CDN
-->
<!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>拖动建筑改变位置</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%}
  .tip{position:absolute;left:12px;top:12px;z-index:5;
       background:rgba(23,28,35,.9);border:1px solid #2a313b;border-radius:6px;
       padding:8px 12px;font-size:12px;color:#a2a9b6;max-width:320px;line-height:1.6}
  .cesium-viewer-bottom .cesium-widget-credits,.cesium-viewer-animationContainer,
  .cesium-viewer-timelineContainer{display:none!important}

</style>
</head>
<body>
<div id="c"></div>
<div class="tip">按住任意建筑拖动，它会跟着光标移动并保持贴地。松手后描边恢复。</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;

  var items = [];
  var seed = 29;
  function rnd() { seed = (seed * 9301 + 49297) % 233280; return seed / 233280; }

  for (var i = 0; i < 9; i++) {
    var h = 18 + rnd() * 30;
    var e = viewer.entities.add({
      position: Cesium.Cartesian3.fromDegrees(116.3880 + (i % 3) * 0.0030,
                                              39.9046 + Math.floor(i / 3) * 0.0026, h / 2),
      box: {
        dimensions: new Cesium.Cartesian3(24, 22, h),
        material: Cesium.Color.fromCssColorString('#4a83d6').withAlpha(0.9),
        outline: true,
        outlineColor: Cesium.Color.WHITE.withAlpha(0.3)
      }
    });
    items.push(e);
  }

  var active = null;
  var ellipsoid = scene.globe.ellipsoid;
  var handler = new Cesium.ScreenSpaceEventHandler(scene.canvas);

  handler.setInputAction(function (down) {
    var picked = scene.pick(down.position);
    if (picked && picked.id && picked.id.box) {
      active = picked.id;
      active.box.outlineColor = Cesium.Color.fromCssColorString('#ffd166');
    }
  }, Cesium.ScreenSpaceEventType.LEFT_DOWN);

  handler.setInputAction(function (move) {
    if (!active) return;
    var cart = viewer.camera.pickEllipsoid(move.endPosition, ellipsoid);
    if (!cart) return;
    var c = Cesium.Cartographic.fromCartesian(cart);
    var dim = active.box.dimensions.getValue();
    active.position = Cesium.Cartesian3.fromRadians(c.longitude, c.latitude, dim.z / 2);
  }, Cesium.ScreenSpaceEventType.MOUSE_MOVE);

  handler.setInputAction(function () {
    if (active) active.box.outlineColor = Cesium.Color.WHITE.withAlpha(0.3);
    active = null;
  }, Cesium.ScreenSpaceEventType.LEFT_UP);

  viewer.camera.flyTo({
    destination: Cesium.Cartesian3.fromDegrees(116.3905, 39.8998, 560),
    orientation: { heading: Cesium.Math.toRadians(14), pitch: Cesium.Math.toRadians(-26), roll: 0 },
    duration: 0
  });
})();
</script>
</body>
</html>