国家/城市标签开启深度测试，背面不渲染

src/scene/CesiumGlobe.js

@@ -414,6 +414,10 @@ export class CesiumGlobe {
       const textGold = Cesium.Color.fromCssColorString('#e0c46a');
       const black = Cesium.Color.fromCssColorString('#14100d');
 
+      // 国家名用 LabelCollection（避免大量 entity 开销）
+      const countryLabels = new Cesium.LabelCollection({ scene: this.viewer.scene });
+      this.viewer.scene.primitives.add(countryLabels);
+
       const lines = [];
       for (const feature of geojson.features || []) {
         const props = feature.properties || {};
@@ -427,18 +431,17 @@ export class CesiumGlobe {
         if (cname === '中华民国') cname = '中国台湾';
         if (cname && props.LABEL_X != null && props.LABEL_Y != null) {
           const fontSize = areaKm2 > 5e6 ? 30 : areaKm2 > 1.5e6 ? 19 : areaKm2 > 3e5 ? 15 : 12;
-          this.viewer.entities.add({
+          countryLabels.add({
             position: Cesium.Cartesian3.fromDegrees(props.LABEL_X, props.LABEL_Y),
-            label: {
-              text: cname,
-              font: `bold ${fontSize}px "Noto Serif SC", "Songti SC", "STSong", "SimSun", Georgia, serif`,
-              fillColor: black,
-              style: Cesium.LabelStyle.FILL,
-              heightReference: Cesium.HeightReference.CLAMP_TO_GROUND,
-              distanceDisplayCondition: new Cesium.DistanceDisplayCondition(1e6, 1e7),
-              scaleByDistance: new Cesium.NearFarScalar(1e4, 20 / 15, 6e6, 1.0),
-              translucencyByDistance: new Cesium.NearFarScalar(9e6, 1.0, 1e7, 0.0),
-            },
+            text: cname,
+            font: `bold ${fontSize}px "Noto Serif SC", "Songti SC", "STSong", "SimSun", Georgia, serif`,
+            fillColor: black,
+            style: Cesium.LabelStyle.FILL,
+            heightReference: Cesium.HeightReference.CLAMP_TO_GROUND,
+            disableDepthTestDistance: 0, // 背面（视野外）不渲染
+            distanceDisplayCondition: new Cesium.DistanceDisplayCondition(1e6, 1e7),
+            scaleByDistance: new Cesium.NearFarScalar(1e4, 20 / 15, 6e6, 1.0),
+            translucencyByDistance: new Cesium.NearFarScalar(9e6, 1.0, 1e7, 0.0),
           });
         }
 
@@ -517,6 +520,7 @@ export class CesiumGlobe {
         verticalOrigin: Cesium.VerticalOrigin.BOTTOM,
         pixelOffset: new Cesium.Cartesian2(0, -6),
         heightReference: Cesium.HeightReference.CLAMP_TO_GROUND,
+        disableDepthTestDistance: 0, // 背面（视野外）不渲染
         distanceDisplayCondition: ddc,
         translucencyByDistance: tdc,
       });