add rain mixNum param

modules/material/shader/weather/RainShader.glsl

 uniform sampler2D colorTexture;
 varying vec2 v_textureCoordinates;
 uniform float speed;
+uniform float mixNum;
 
 float hash(float x){
   return fract(sin(x*23.3)*13.13);
   float v=1.-sin(hash(floor(uv.x*100.))*2.);
   float b=clamp(abs(sin(20.*time*v+uv.y*(5./(2.+v))))-.95,0.,1.)*10.;
   c*=v*b;
-  gl_FragColor = mix(texture2D(colorTexture, v_textureCoordinates), vec4(c,1), 0.5);
+  gl_FragColor = mix(texture2D(colorTexture, v_textureCoordinates), vec4(c,1), mixNum);
 }

modules/weather/type/Rain.js

     this._delegate = undefined
     this._enable = false
     this._speed = 10.0
+    this._mixNum = 0.5
     this._state = State.INITIALIZED
   }
 
     return this._speed
   }
 
+  set mixNum(mixNum) {
+    this._mixNum = mixNum
+    this._delegate && (this._delegate.uniforms.mixNum = mixNum)
+    return this
+  }
+
+  get mixNum() {
+    return this._mixNum
+  }
+
   /**
    *
    * @private
       name: this._id,
       fragmentShader: RainShader,
       uniforms: {
-        speed: this._speed
+        speed: this._speed,
+        mixNum: this._mixNum
       }
     })
     this._viewer.scene.postProcessStages.add(this._delegate)