Unity shader realizes diffuse reflection and shadowing of multiple light sources

Shader "Unlit/MulLight"
{
 Properties
 {
  _MainTex ("Texture", 2D) = "white" {}
 }
 SubShader
 {
  //A main light  Pass
  {
   //Always: Always rendering; no lighting mode.   //ForwardBase: Suitable for front rendering, environment, main direction light, light/sh light and baking pictures.   //ForwardAdd: Suitable for front rendering, if you superimpose each lamp, each lamp will have an extra pass.   //Deferred: Delay rendering, rendering g buffer.   //ShadowCaster: Render the object depth to a shadow map or depth texture.   //PrepassBase: Used for traditional delay lighting, rendering normals and highlights.   //PrepassFinal: used in traditional delayed lighting, rendering the final result by combining literature, lighting, and normals.   //Vertex: When the object is not a light map, it is used for rendering of legacy vertices, and all vertex lights are used.   //VertexLMRGBM: When an object is lightly mapped, rendering is used on legacy vertices, on platforms where LightMap is RGBM-encoded (pc and console).   //VertexLM: When an object is lightly mapped, rendering is used on legacy vertices, on a platform where LightMap is a dual idr encoding (mobile platform).   Tags { "RenderType"="Opaque" "LightMode" = "ForwardBase"}//////
   CGPROGRAM
   #pragma vertex vert
   #pragma fragment frag
   #include ""
    #pragma target 3.0 
 
   //Implementation of attenuation and shadow   #include ""//////
    //fwdadd: The shadow of ForwardBase is displayed. In the ForwardAdd below, fwdadd must be used; it must be combined with fallback, both are indispensable.   #pragma multi_compile_fwdadd_fullshadows//////
   sampler2D _MainTex;
   float4 _MainTex_ST;
   //Define a light with a fixed format, and will automatically retrieve the light in the scene   float4 _LightColor0;//////
 
   struct appdata
   {
    float4 vertex : POSITION;
    float2 uv : TEXCOORD0;
    float4 normal:NORMAL;//////
   };
 
   struct v2f
   {
    float2 uv : TEXCOORD0;
    float4 pos: SV_POSITION;
    float3 normal :TEXCOORD1;//////
     //Attenuation required by the point light source    LIGHTING_COORDS(3,4)//////#include ""
   };
   v2f vert (appdata v)
   {
    v2f o;
    //It is usually used here, and sometimes it will cause an error when used.    = UnityObjectToClipPos();
     = TRANSFORM_TEX(, _MainTex);
     = ;//////
    //Attenuation required by the point light source    TRANSFER_VERTEX_TO_FRAGMENT(o)//////#include ""
    return o;
   }
   fixed4 frag (v2f i) : SV_Target
   {
    //The object normal vector is converted into world normal vector    float3 N = normalize(UnityObjectToWorldNormal());//////
    //World light vector: Unit encapsulated light vector will automatically call the existing lights in the scene    float3 L =normalize( _WorldSpaceLightPos0.xyz);//////
             //The attenuation coefficient required by the point light source    float atten = LIGHT_ATTENUATION(i);//////#include ""
 
    fixed4 col = tex2D(_MainTex, );
    // Final color = main color x (light color x diffuse coefficient x attenuation coefficient + ambient light)     =  * (_LightColor0.rgb* saturate(dot(N,L)) *atten + UNITY_LIGHTMODEL_AMBIENT);//////
 
    return col;
   }
   ENDCG
   }
 
   //Add multiple lamps  Pass//////
  {
   Tags { "RenderType"="Opaque" "LightMode" = "ForwardAdd"} //ForwardAdd: Multi-Lamp Mix////////   Blend One One//////
   CGPROGRAM
   #pragma vertex vert
   #pragma fragment frag
   #include ""
   #pragma target 3.0
 
   //Implementation of attenuation and shadow   #include ""//////
    //fwdadd: The shadow of ForwardAdd is displayed. Fwdbase must be used in the ForwardBase above; it must be combined with fallback, both are indispensable.   #pragma multi_compile_fwdadd_fullshadows//////
 
   sampler2D _MainTex;
   float4 _MainTex_ST;
   //Define a light with a fixed format, and will automatically retrieve the light in the scene   float4 _LightColor0;//////
 
   struct appdata
   {
    float4 vertex : POSITION;
    float2 uv : TEXCOORD0;
    float4 normal:NORMAL;//////
   };
 
   struct v2f
   {
    float2 uv : TEXCOORD0;
    float4 pos: SV_POSITION;
    float3 normal :TEXCOORD1;//////
    float4 wPos :TEXCOORD2;//////
    //Attenuation required by the point light source    LIGHTING_COORDS(3,4)//////#include ""
   };
   v2f vert (appdata v)
   {
    v2f o;
     //It is usually used here, and sometimes it will cause an error when used.    = UnityObjectToClipPos();
     = TRANSFORM_TEX(, _MainTex);
    = mul(unity_ObjectToWorld, );//////
     = ;//////
    //Attenuation required by the point light source    TRANSFER_VERTEX_TO_FRAGMENT(o)//////#include ""
    return o;
   }
   fixed4 frag (v2f i) : SV_Target
   {
    //The object normal vector is converted into world normal vector    float3 N = normalize(UnityObjectToWorldNormal());//////
 
    //World light vector: Here is the point light source, and the attenuation is calculated according to the distance of the light. The first pass does not need to    float3 L = normalize (lerp(_WorldSpaceLightPos0.xyz , _WorldSpaceLightPos0.xyz -  , _WorldSpaceLightPos0.w));//////
 
    //Attenuation required by the point light source    float atten = LIGHT_ATTENUATION(i);//////#include ""
 
    fixed4 col = tex2D(_MainTex, );
 
    // Final color = main color x light color x diffuse coefficient x attenuation coefficient The first pass already has an environment color. You can't add it here     =  * _LightColor0.rgb * saturate(dot(N,L))*atten;//////
 
    return col;
   }
  ENDCG
  }
 }
   //Shadows need to be generated   FallBack "Diffuse" 
}