Unity Shader如何实现雨天的水面涟漪效果

Shader "Custom/Ripple" {  Properties {    _Color ("Color", Color) = (1,1,1,1)    _MainTex ("Albedo (RGB)", 2D) = "white" {}    _Glossiness ("Smoothness", Range(0,1)) = 0.5    _Metallic ("Metallic", Range(0,1)) = 0.0    _RippleTex("RippleTex", 2D) = "white" {}    _RippleScale("RippleScale",Range(1,10)) =1
  }  SubShader {    Tags { "RenderType"="Opaque" }    LOD 200
    CGPROGRAM    // Physically based Standard lighting model, and enable shadows on all light types    #pragma surface surf Standard fullforwardshadows    #pragma target 3.0    #define PI 3.141592653    sampler2D _MainTex;
    struct Input {      float2 uv_MainTex;      half2 texcoord;    };
    half _Glossiness;    half _Metallic;    fixed4 _Color;    sampler2D _RippleTex;    float _RippleScale;    UNITY_INSTANCING_BUFFER_START(Props)    UNITY_INSTANCING_BUFFER_END(Props)
    //计算波纹的主函数    float3 ComputeRipple(float2 uv, float t)    {      //波纹贴图采样，并把采样的高度值扩展到-1到1。      float4 ripple = tex2D(_RippleTex, uv);      ripple.yz = ripple.yz * 2.0 - 1.0;      //获取波纹的时间,从A通道获取不同的波纹时间,      float dropFrac = frac(ripple.a + t);      //把时间限制在R通道内      float timeFrac = dropFrac - 1.0 + ripple.x;      //做淡出处理      float dropFactor = 1-saturate( dropFrac);      //计算最终的高度，用一个sin计算出随时间的振幅，修改一下值就知道什么效果了      float final = dropFactor* sin(clamp(timeFrac * 9.0, 0.0, 4.0) * PI);      return float3(ripple.yz * final, 1.0);    }
    void surf (Input IN, inout SurfaceOutputStandard o) {      fixed4 c = tex2D (_MainTex, IN.uv_MainTex) * _Color;      o.Albedo = c.rgb;
      //调用方法，获取高度。这里我懒得用一个新uv，索性直接用的主贴图UV      float3 ripple = ComputeRipple(IN.uv_MainTex / _RippleScale, _Time.y);      // Metallic and smoothness come from slider variables      o.Metallic = _Metallic;      o.Smoothness = _Glossiness;      //赋值到法线上      o.Normal = ripple;      o.Alpha = c.a;    }    ENDCG  }  FallBack "Diffuse"}