unity3d实现描边shader

Shader "Custom/OutLine" {Properties {
        _Color ("Main Color", Color) = (.5,.5,.5,1)
        _OutlineColor ("Outline Color", Color) = (0,0,0,1)
        _Outline ("Outline width", Range (0.0, 0.03)) = .005
        _MainTex ("Base (RGB)", 2D) = "white" { }
    }
    CGINCLUDE
        #include "UnityCG.cginc"
        struct appdata {
            float4 vertex : POSITION;
            float3 normal : NORMAL;
        };
        struct v2f {
            float4 pos : POSITION;
            float4 color : COLOR;
        };
        uniform float _Outline;
        uniform float4 _OutlineColor;
        v2f vert(appdata v) {
            v2f o;
            o.pos = mul(UNITY_MATRIX_MVP, v.vertex);
            float3 norm   = mul ((float3x3)UNITY_MATRIX_IT_MV, v.normal);
            float2 offset = TransformViewToProjection(norm.xy);
            o.pos.xy += offset * o.pos.z * _Outline;
            o.color = _OutlineColor;
            return o;
        }
    ENDCG
    SubShader {
        Tags { "Queue" = "Transparent" }
        Pass {
            Tags { "LightMode" = "Always" }
            Cull Off
            ZWrite Off
            //ZTest Always//始终通过深度测试，即可以渲染
            //ColorMask RGB // alpha not used
            Blend SrcAlpha OneMinusSrcAlpha // Normal

            CGPROGRAM
            #pragma vertex vert
            #pragma fragment frag
            half4 frag(v2f i) :COLOR {
                return i.color;
            }
            ENDCG
        }
        Pass {
            Name "BASE"
            ZWrite On
            ZTest LEqual
            Blend SrcAlpha OneMinusSrcAlpha
            Material {
                Diffuse [_Color]
                Ambient [_Color]
            }
            Lighting On
            SetTexture [_MainTex] {
                ConstantColor [_Color]
                Combine texture * constant
            }
            SetTexture [_MainTex] {
                Combine previous * primary DOUBLE
            }
        }
    }
    Fallback "Diffuse"
}