Unity Shader 菲涅尔环境反射

菲涅尔反射描述了一种光学现象，当光照到物体表面时，一部分发生反射，另一部分则进入物体内部，发生折射或散射；相比直接的反射和折射计算，菲涅尔反射更接近真实情况。

可用下面的等式近似计算这种反射效果：

F=F0+(1-F0)*pow((1-dot(v,n)),p);

其中，F0为反射系数，v为视野方向，n为法线方向，p为控制指数，一般p=5。

代码如下：

 Shader "MyUnlit/FresnelReflection"
 {
     Properties
     {
         _Color("Color Tint", Color) = (,,,)
         _ReflectColor("Reflection Color",Color) = (,,,)
         _FresnelScale("Fresnel Scale",range(,)) = 0.5
         _CubeMap("Reflection CubeMap",cube) = "_skybox"{}
     }
         SubShader
     {
         Tags{ "RenderType" = "Opaque" }

         Pass
     {
         Tags{ "lightmode" = "forwardbase" }

         CGPROGRAM
         #pragma multi_compile_fwdbase
         #pragma vertex vert
         #pragma fragment frag

         #include "UnityCG.cginc"
         #include "autolight.cginc"
         #include "lighting.cginc"

         fixed4 _Color;
         fixed4 _ReflectColor;
         fixed _FresnelScale;
         samplerCUBE _CubeMap;

     struct appdata
     {
         float4 vertex : POSITION;
         float3 normal:NORMAL;
     };

     struct v2f
     {
         float3 worldPos : TEXCOORD0;
         float4 pos : SV_POSITION;
         float3 worldNormal:TEXCOORD1;
         float3 worldViewDir:TEXCOORD2;
         float3 worldRef:TEXCOORD3;
         SHADOW_COORDS()
     };

     v2f vert(appdata v)
     {
         v2f o;
         o.pos = UnityObjectToClipPos(v.vertex);
         o.worldNormal = UnityObjectToWorldNormal(v.normal);
         o.worldPos = mul(unity_ObjectToWorld, v.vertex).xyz;
         o.worldViewDir = UnityWorldSpaceViewDir(o.worldPos);
         o.worldRef = reflect(-o.worldViewDir, o.worldNormal);

         TRANSFER_SHADOW(o);
         return o;
     }

     fixed4 frag(v2f i) : SV_Target
     {
         fixed3 worldNormal = normalize(i.worldNormal);
         fixed3 worldViewDir = normalize(i.worldViewDir);
         fixed3 worldLightDir = normalize(UnityWorldSpaceLightDir(i.worldPos));

         fixed3 ambient = UNITY_LIGHTMODEL_AMBIENT.xyz;
         fixed3 col = texCUBE(_CubeMap, i.worldRef).rgb;
         fixed3 reflection = col * _ReflectColor.rgb;

         fixed3 diffuse = _LightColor0.rgb*_Color.rgb*saturate(dot(worldNormal, worldLightDir));
         fixed fresnel = _FresnelScale + ( - _FresnelScale)*pow( - dot(worldViewDir, worldNormal), );

         UNITY_LIGHT_ATTENUATION(atten, i, i.worldPos);
         fixed3 color = ambient + lerp(diffuse, reflection, saturate(fresnel))*atten;
         return fixed4(color,1.0);
     }
         ENDCG
     }
     }
         fallback "Reflective/VertexLit"
 }