简单的积雪shader

// Upgrade NOTE: replaced '_World2Object' with 'unity_WorldToObject'

Shader "Custom/CoverSnow"
{
    Properties
    {
        _MainTex ("Texture", 2D) = "white" {}
        _SnowLevel ("Snow Level", Range(0,1) ) = 0  
        _SnowColor ("Snow Color", Color) = (1.0,1.0,1.0,1.0)  
        _Wetness ("Wetness", Range(0, 0.5)) = 0.3  
    }
    SubShader
    {
        Tags { "RenderType"="Opaque" }
        LOD 100

        Pass
        {
            CGPROGRAM
            #pragma vertex vert
            #pragma fragment frag
            // make fog work
            #pragma multi_compile_fog
            
            #include "UnityCG.cginc"

            struct appdata
            {
                float4 vertex : POSITION;
                float3 normal:NORMAL;
                float2 uv : TEXCOORD0;
            };

            struct v2f
            {
                float2 uv : TEXCOORD0;
                float3 worldNormal:TEXCOORD1;
                UNITY_FOG_COORDS(1)
                float4 vertex : SV_POSITION;
            };

            sampler2D _MainTex;
            float4 _MainTex_ST;
            float _SnowLevel;  
            float4 _SnowColor;  
            float _Wetness;  
            
            v2f vert (appdata v)
            {
                v2f o;
                o.vertex = UnityObjectToClipPos(v.vertex);
                o.worldNormal = normalize(mul(v.normal,(float3x3)unity_WorldToObject));
                o.uv = TRANSFORM_TEX(v.uv, _MainTex);
                UNITY_TRANSFER_FOG(o,o.vertex);
                return o;
            }
            
            fixed4 frag (v2f i) : SV_Target
            {
                // sample the texture
                fixed4 col = tex2D(_MainTex, i.uv);
                half difference = dot(i.worldNormal, float3(0,1,0)) - lerp(1,-1,_SnowLevel);  //这里减0.7（2分之根号2）代表小于等于45度的夹角，不减是90度的夹角，cos60=0.5,cos45=sqrt(2)/2
                  difference = saturate(difference / _Wetness);  
                 col.rgb = difference*_SnowColor.rgb + (1-difference) * col.rgb;  
                // apply fog
                UNITY_APPLY_FOG(i.fogCoord, col);
                return col;
            }
            ENDCG
        }
    }
}