Unity3D Shader落雪效果

Shader "Custom/Snow" {
    Properties {
        _MainTex ("Base (RGB)", 2D) = "white" {}
        _RimColor("Rim Color", Color) = (1,1,1,1)
        _SnowPower ("Snow Power",range(0,1)) = 0.2//边缘强度
        _SnowRang("Snow Range",range(0,1)) = 0.1
    }

    SubShader {

        Pass
        {

        CGPROGRAM

        #include "UnityCG.cginc"

        struct v2f
        {
            float4 vertex:POSITION;
            float2 uv:TEXCOORD0;
            float3 normal:TEXCOORD1;
            float rim:COLOR;
        };

        sampler2D _MainTex;
        float4 _RimColor;
        float _SnowPower;
        float _SnowRang;

        v2f vert(appdata_base  v)
        {
            v2f o;

            o.uv = v.texcoord;

            float3 sn = mul((float3x3)_World2Object, float3(0,1,0));

            o.normal = normalize(mul((float3x3)_Object2World,v.normal));
            float diff = saturate(dot(v.normal,sn));
            if( 1-diff<_SnowRang)
            {
                v.vertex.xyz+=normalize(diff*sn+(1-diff)*v.normal)*_SnowPower;
            }

            o.vertex = mul(UNITY_MATRIX_MVP, v.vertex);
            return o;
        }

        fixed4 frag (v2f IN):COLOR
        {
            fixed4  c = tex2D(_MainTex, IN.uv);
            float diff = saturate(dot(float3(0,1,0),IN.normal));

            if(1-diff<_SnowRang)
            {
                float range = (diff/0.8)*(diff/0.8);
                //c.rgb = _RimColor.rgb*range+c.rgb*(1-range);
                c.rgb = _RimColor.rgb;
            }

            return c;
        }

        #pragma vertex vert
        #pragma fragment frag

        ENDCG
        }
    }
    FallBack "Diffuse"
}