Picking and scene interaction

• Branch on picked.id instanceof Entity versus Cesium3DTileFeature before reading properties.
• Use drillPick with a limit to cycle through stacked features at one pixel.
• Call pickPosition first and fall back to pickEllipsoid when the depth buffer misses.

var handler = new Cesium.ScreenSpaceEventHandler(viewer.scene.canvas);

handler.setInputAction(function (movement) {
  var picked = viewer.scene.pick(movement.position);

  if (!Cesium.defined(picked)) {
    console.log('点到了空白处');
    return;
  }

  if (picked.id instanceof Cesium.Entity) {
    console.log('实体', picked.id.name, picked.id.properties);
  } else if (picked instanceof Cesium.Cesium3DTileFeature) {
    console.log('瓦片要素', picked.getProperty('name'));
  } else {
    console.log('图元', picked.primitive);
  }
}, Cesium.ScreenSpaceEventType.LEFT_CLICK);

var cycle = 0;
var lastPixel = null;

handler.setInputAction(function (movement) {
  var pos = movement.position;

  if (!lastPixel || lastPixel.x !== pos.x || lastPixel.y !== pos.y) {
    cycle = 0;
    lastPixel = pos;
  }

  var stack = viewer.scene.drillPick(pos, 6);
  if (stack.length === 0) return;

  cycle = (cycle + 1) % stack.length;
  var target = stack[cycle];
  console.log('第', cycle + 1, '层', target.id && target.id.name);
}, Cesium.ScreenSpaceEventType.LEFT_CLICK);

• Picking uses the previous frame, so an entity added in the same tick may return undefined.
• Translucent geometry needs scene.pickTranslucentDepth = true to be pickable.