主角场景Shader效果：遮挡透明

基本原理：被遮挡的部分关闭深度写入， 显示透明效果；未被遮挡的部分不关闭深度测试，显示正常贴图效果，即使用两个Pass即可。

Pass1：关闭深度写入（ZWrite Off），深度测试渲染较远的物体，即模型被物体遮挡的部分（ztest greater）。

Pass2：开启深度写入，正常渲染。

 Shader "xj/Character/Normal" {
     Properties {
         _Color ("Main Color", Color) = (,,,)
         _MainTex ("Base (RGB) Trans (A)", 2D) = "white" {}
         _intensity ("Intensity", float ) = 1.0

         _RimColor("RimColor",Color) = (,,,)
         _RimPower ("Rim Power", Range(0.1,8.0)) = 1.0
     }

     SubShader
     {
         LOD
         Tags { "Queue" = "Geometry+500" "RenderType"="Opaque" }
         Pass
         {
             Blend SrcAlpha One
             ZWrite off
             Lighting off

             ztest greater

             CGPROGRAM
             #pragma vertex vert
             #pragma fragment frag
             #include "UnityCG.cginc"

             float4 _RimColor;
             float _RimPower;

             struct appdata_t {
                 float4 vertex : POSITION;
                 float2 texcoord : TEXCOORD0;
                 float4 color:COLOR;
                 float4 normal:NORMAL;
             };

             struct v2f {
                 float4  pos : SV_POSITION;
                 float4  color:COLOR;
             } ;
             v2f vert (appdata_t v)
             {
                 v2f o;
                 o.pos = mul(UNITY_MATRIX_MVP,v.vertex);
                 float3 viewDir = normalize(ObjSpaceViewDir(v.vertex));
                 //视线与法线垂直的部分（点乘为0）即是外轮廓，加重描绘
                 float rim =  - saturate(dot(viewDir,v.normal ));
                 o.color = _RimColor*pow(rim,_RimPower);
                 return o;
             }
             float4 frag (v2f i) : COLOR
             {
                 return i.color;
             }
             ENDCG
         }
         Pass {
             CGPROGRAM
                 #pragma vertex vert
                 #pragma fragment frag
                 #pragma fragmentoption ARB_precision_hint_fastest

                 #include "UnityCG.cginc"

                 struct appdata_t {
                     float4 vertex : POSITION;
                     half2 texcoord : TEXCOORD0;
                 };

                 struct v2f {
                     float4 vertex : SV_POSITION;
                     half2 texcoord : TEXCOORD0;
                 };

                 sampler2D _MainTex;
                 fixed4 _Color;
                 fixed _intensity;

                 v2f vert (appdata_t v)
                 {
                     v2f o;
                     o.vertex = mul(UNITY_MATRIX_MVP,v.vertex);
                     o.texcoord = v.texcoord;
                     return o;
                 }

                 fixed4 frag (v2f i) : SV_Target
                 {
                     fixed4 col = tex2D(_MainTex, i.texcoord) * _Color * _intensity;
                     return col;
                 }
             ENDCG
         }
     }
 }