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) = (1,1,1,1)
        _ReflectColor("Reflection Color",Color) = (1,1,1,1)
        _FresnelScale("Fresnel Scale",range(0,1)) = 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(4)
    };

    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 + (1 - _FresnelScale)*pow(1 - dot(worldViewDir, worldNormal), 5);

        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"
}