参考 https://blog.csdn.net/xiaoge132/article/details/77801931

//全息效果
Shader "Custom/Silhouette"
{
    Properties
    {
        _MainTex ("Texture", 2D) = "white" {}
        _Color("Color", Color) = (1,1,1,1)
        _DotProduct("Rim effect", Range(-1,1)) = 0.25
    }
    SubShader
    {
        Tags {
            "Queue" = "Transparent"
            "IgnoreProjector" = "True"
            "RenderType" = "Transparent"
            "LightMode" = "ForwardBase"
        }

        LOD 200
        Cull Off

        Pass
        {
            Blend SrcAlpha OneMinusSrcAlpha

            CGPROGRAM
            #pragma vertex vert
            #pragma fragment frag

            #include "UnityCG.cginc"

            struct appdata
            {
                float4 vertex : POSITION;
                //模型空间法线
                float3 normal : NORMAL;
                float2 uv : TEXCOORD0;
            };

            struct v2f
            {
                float2 uv : TEXCOORD0;
                float4 vertex : SV_POSITION;
                //世界空间法线
                float3 worldNormal : TEXCOORD1;
                //世界空间坐标
                float3 worldPosition : TEXCOORD2;
            };

            sampler2D _MainTex;
            float4 _MainTex_ST;
            fixed4 _Color;
            fixed _DotProduct;

            v2f vert (appdata v)
            {
                v2f o;
                o.vertex = UnityObjectToClipPos(v.vertex);
                o.uv = TRANSFORM_TEX(v.uv, _MainTex);
                o.worldNormal = UnityObjectToWorldNormal(v.normal);
                o.worldPosition = mul(unity_ObjectToWorld, v.vertex).xyz;
                return o;
            }

            fixed4 frag (v2f i) : SV_Target
            {
                fixed3 worldNormal = normalize(i.worldNormal);
                fixed3 viewDir = normalize(UnityWorldSpaceViewDir(i.worldPosition));

                //因为viewDir和worldNormal都是归一化矢量,点乘后的值为它们夹角的cos值。
                //考虑到半透明物体需要双面渲染, 所以对点乘结果求绝对值abs。
                float border = 1 - (abs(dot(viewDir, worldNormal)));
                //_DotProduct: 调整透明度
                float alpha = (border * (1 - _DotProduct) + _DotProduct);

                float4 c = tex2D(_MainTex, i.uv) * _Color;
                c.a = alpha;
                return c;
            }
            ENDCG
        }
    }
}