(function (Cesium) {
    function RainEffect(viewer, options) {
        if (!viewer) throw new Error("viewer is undefined")
        this.viewer = viewer;
        this.speed = Cesium.defaultValue(options.speed, 10)
        this.size = Cesium.defaultValue(options.size, 20)
        this.direction = Cesium.Math.toRadians(Cesium.defaultValue(options.direction, -30));
        this.enabled = Cesium.defaultValue(options.enabled, true)
        this.init();
    }

    RainEffect.prototype.init = function () {
        this.rainStage = new Cesium.PostProcessStage({
            name: 'czm_rain',
            fragmentShader: this.FragmentShader_Rain(),
            uniforms: {
                direction: () => { return this.direction },
                size: () => { return this.size; },
                speed: () => { return this.speed; }
            }
        });
        this.rainStage.enabled = this.enabled
        this.viewer.scene.postProcessStages.add(this.rainStage)
    }

    //定义下雨场景 着色器
    RainEffect.prototype.FragmentShader_Rain = function () {
        return `uniform sampler2D colorTexture;//下雨前输入的场景渲染照片
    varying vec2 v_textureCoordinates;
    uniform float speed;
    uniform float size;
    uniform float direction;
    
    
    float hash(float x){
        return fract(sin(x*23.3)*13.13);
    }
    
    void main(void){
    
        float time = czm_frameNumber * speed / 1000.0;
        vec2 resolution = czm_viewport.zw;
    
        vec2 uv=(gl_FragCoord.xy*2.-resolution.xy)/min(resolution.x,resolution.y);
        vec3 finalColor=vec3(0.1,0.2,0.3);//粒子的颜色
    
        float si=sin(direction),co=cos(direction);
        uv*=mat2(co,-si,si,co);
        uv*=length(uv+vec2(0,4.9))*0.3+1.0;
    
        float v=1.-sin(hash(floor(uv.x*100.0))*2.0);
        float b=clamp(abs(sin(20.0*time*v+uv.y*(5./(2.0+v))))-.95,0.0,1.0)*size;
        finalColor*=v*b; //屏幕上雨的颜色
    
        gl_FragColor = mix(texture2D(colorTexture, v_textureCoordinates), vec4(finalColor,1.0), 0.5); //将雨和三维场景融合
    }
    `
    }

    RainEffect.prototype.show = function (visible) {
        this.rainStage.enabled = visible;
    }

    RainEffect.prototype.destroy = function () {
        if (!this.viewer || !this.rainStage) return;
        this.viewer.scene.postProcessStages.remove(this.rainStage);
        this.rainStage.destroy();
        delete this.direction
        delete this.size
        delete this.speed
    }

    Cesium.RainEffect = RainEffect
})(Cesium)