Cesium 封装积雪效果

/*
 * @Descripttion: 
 * @version: 1.0
 * @Author: tanzheng
 * @Date: 2024-1-23 15:30:42
 */
/**
 * 
 * 封装天气场景
 * 积雪
 */
class SnowCover{

    constructor(viewer){
        
    }
    //创建雪
    createSnowCover(){
        this.collection = viewer.scene.postProcessStages;
        this._snowCover = new Cesium.PostProcessStage({
            name: 'czm_snowcover',
            fragmentShader: this.getSnowCover(),
            // uniforms: {
            //     snowIntensity: 3.0, // 积雪厚度, 0~1
            //   }
        });
        this.collection.add(this._snowCover);
        viewer.scene.skyAtmosphere.hueShift = -0.8;
        viewer.scene.skyAtmosphere.saturationShift = -0.7;
        viewer.scene.skyAtmosphere.brightnessShift = -0.33;
        viewer.scene.fog.density = 0.001;
        viewer.scene.fog.minimumBrightness = 0.8;
        
    }
    //获得雪的shader
    getSnowCover(){
        
        var fs= `