先來看下效果:

原理很簡單，首先獲取頂點到攝像機的觀察方向，然後與頂點的法線方向進行點積算出投影的長度最後再乘以我們設定的顏色值即為最終要輸出的顏色。這裡要注意觀察方向與法線方向要進行歸一化。

shader程式碼:

Shader "Custom/XLight" {
	Properties {
		_Color ("Color", Color) = (1,1,1,1)
		_MainTex ("Albedo (RGB)", 2D) = "white" {}
	}
    
	SubShader {
		Tags{"IgnoreProjector"="True" "LightMode" = "ForwardBase" "Queue"="Transparent" "RenderType"="Transparent"}  

        Pass  
        {  
            Blend SrcAlpha OneMinusSrcAlpha  
            ZWrite Off  

            CGPROGRAM  

            #include "Lighting.cginc"  
            #pragma vertex vert  
            #pragma fragment frag 

            fixed4 _Color;  
            struct v2f  
            {  
                float4 pos : SV_POSITION;  
                float3 normal : normal;  
                float3 viewDir : TEXCOORD0;  
            };  
          
            v2f vert (appdata_base v)  
            {  
                v2f o;  
                o.pos = mul(UNITY_MATRIX_MVP, v.vertex);  
                o.viewDir = ObjSpaceViewDir(v.vertex);  
                o.normal = v.normal;  
                return o;  
            }  
          
            fixed4 frag(v2f i) : SV_Target  
            {  
                float3 normal = normalize(i.normal);  
                float3 viewDir = normalize(i.viewDir);  
                float rim = 1 - dot(normal, viewDir);  
                return _Color * rim;  
            }   
            ENDCG  
        }  
	}
	FallBack "Diffuse"
}