Unity图形学之折射

1.折射原理：

2.反射的计算实现：入射角I- 2倍的N * 点乘(N,I)

float3  reflect(float3  I ,float3 N)
{
   return  I-2.0*N*dot(N,I) ;
}

3.折射的计算实现公式：看折射率多大  EtaRatio: 折射率

float3 refract(float3 I, float3 N, float  etaRatio)
{
    float  cosI = dot(-I,N) ;
    float  cosI2 = 1.0f-etaRatio*etaRatio*(1.0f -cosI*cosI) ;
    float3 T = eatRatio*I +((eatRatio*cosI- sqrt(abs(cosI2)))*N) ;
    return   T*(float3)(cosI2>0) ;
}

Shader "Custom/Refrect"
{
    Properties
    {
        _Color ("Color", Color) = (1,1,1,1)
        _MainTex ("Albedo (RGB)", 2D) = "white" {}
        _Rate("Rate",float) = 1.1
        _CubeMap("Cube Map",CUBE) = "" {}
    }
    SubShader
    {
        Tags { "RenderType"="Opaque" }
        LOD 200
        CGPROGRAM
        // Physically based Standard lighting model, and enable shadows on all  light types
        #pragma surface surf Lambert vertex:MyVertex
        // Use shader model 3.0 target, to get nicer looking lighting
        #pragma target 3.0
        sampler2D _MainTex;
        samplerCUBE _CubeMap;
        struct Input
        {
            float2 uv_MainTex;
            float3 refr;
        };
       
        fixed4 _Color;
        float _Rate;
        void MyVertex(inout appdata_full v,out Input data)
        {
            UNITY_INITIALIZE_OUTPUT(Input,data);
            //由世界坐标系的法线 变成 物体坐标系的法线 然后变成单位向量
            float3 localNormal =   normalize(mul(v.normal,(float3x3)unity_WorldToObject) );
            //观察者入射角
            float3 viewDir =  -WorldSpaceViewDir(v.vertex);
            data.refr = refract(viewDir,localNormal,_Rate);
        }
        void surf (Input IN, inout SurfaceOutput o)
        {
            // Albedo comes from a texture tinted by color
            fixed4 c = tex2D (_MainTex, IN.uv_MainTex) * _Color;
            
            
            o.Albedo =  texCUBE(_CubeMap,IN.refr).rgb;
            //o.Albedo = c.rgb;
            
            o.Alpha = c.a;
        }
        ENDCG
    }
    FallBack "Diffuse"
}