原理
勾勒轮廓光，越边缘的地方越亮，而边缘一般是与法线垂直，所以有如下公式：

half rim = 1.0 - saturate(dot (viewDir, Normal));

实现效果：

image.png

Shader "Unlit/Xray"
{
    Properties
    {
        _RimColor("RimColor", Color) = (0, 0, 1, 1)
        _RimIntensity("Intensity", Range(0, 2)) = 1
    }
    SubShader
    {
        Tags { 
            "Queue" = "Transparent"
            "RenderType"="Opaque" }
        LOD 100

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

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

            struct v2f
            {
                float4 color : COLOR;
                float4 vertex : SV_POSITION;
            };

            float _RimIntensity;
            float4 _RimColor;
            //half rim = 1.0 - saturate(dot (viewDir, Normal));
            v2f vert (appdata v)
            {
                v2f o;
                o.vertex = UnityObjectToClipPos(v.vertex);
                float3 viewDir = normalize(WorldSpaceViewDir(v.vertex));
                float3 normal = mul(unity_ObjectToWorld,v.normal).xyz;
                half rim = 1.0 - saturate(dot(viewDir,normal));
                o.color = _RimColor * pow(rim,_RimIntensity);
                UNITY_TRANSFER_FOG(o,o.vertex);
                return o;
            }
            
            fixed4 frag (v2f i) : SV_Target
            {
                // sample the texture
                fixed4 col = i.color;
                // apply fog
                UNITY_APPLY_FOG(i.fogCoord, col);
                return col;
            }
            ENDCG
        }
    }
}

加入法线纹理

image2.png

Shader "Unlit/XrayNormal"
{
    Properties
    {
        _RimColor("RimColor", Color) = (0, 0, 1, 1)
        _RimIntensity("Intensity", Range(0, 2)) = 1
        _BumpMap("Bump Map",2D) = "white"{}
    }
    SubShader
    {
        Tags { 
            "Queue" = "Transparent"
            "RenderType"="Opaque" }
        LOD 100

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

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

            struct v2f
            {
                float2 uv     : TEXCOORD0;
                float4 color  : COLOR;
                float4 vertex : SV_POSITION;
                float3 viewDir: TEXCOORD1;
            };

            float _RimIntensity;
            float4 _RimColor;
            sampler2D _BumpMap;
            //half rim = 1.0 - saturate(dot (normalize(IN.viewDir), o.Normal));
            v2f vert (appdata v)
            {
                v2f o;
                o.vertex = UnityObjectToClipPos(v.vertex);
                TANGENT_SPACE_ROTATION;
                o.viewDir = normalize(mul(rotation,ObjSpaceViewDir(v.vertex)));
                                o.uv = v.uv;
                return o;
            }
            
            fixed4 frag (v2f i) : SV_Target
            {
                fixed3 tangentNormal = UnpackNormal(tex2D(_BumpMap,i.uv));
                half rim = 1.0 - saturate(dot(i.viewDir,tangentNormal));
                fixed4 col = _RimColor * pow(rim,_RimIntensity);
                return col;
            }
            ENDCG
        }
    }
}

参考
资源
源码