Refraction-折射

// Upgrade NOTE: replaced '_Object2World' with 'unity_ObjectToWorld'
// Upgrade NOTE: replaced 'mul(UNITY_MATRIX_MVP,*)' with 'UnityObjectToClipPos(*)'

Shader "Unity Shaders Book/Chapter 10/Refraction" {
   Properties {
       _Color ("Color Tint", Color) = (1, 1, 1, 1)
       _RefractColor ("Refraction Color", Color) = (1, 1, 1, 1)
       _RefractAmount ("Refraction Amount", Range(0, 1)) = 1
       _RefractRatio ("Refraction Ratio", Range(0.1, 1)) = 0.5
       _Cubemap ("Refraction Cubemap", Cube) = "_Skybox" {}
   }
   SubShader {
       Tags { "RenderType"="Opaque" "Queue"="Geometry"}

       Pass {
           Tags { "LightMode"="ForwardBase" }

           CGPROGRAM

           #pragma multi_compile_fwdbase

           #pragma vertex vert
           #pragma fragment frag

           #include "Lighting.cginc"
           #include "AutoLight.cginc"

           fixed4 _Color;
           fixed4 _RefractColor;
           float _RefractAmount;
           fixed _RefractRatio;
           samplerCUBE _Cubemap;

           struct a2v {
               float4 vertex : POSITION;
               float3 normal : NORMAL;
           };

           struct v2f {
               float4 pos : SV_POSITION;
               float3 worldPos : TEXCOORD0;
               fixed3 worldNormal : TEXCOORD1;
               fixed3 worldViewDir : TEXCOORD2;
               fixed3 worldRefr : TEXCOORD3;
               SHADOW_COORDS(4)
           };

           v2f vert(a2v 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);

               // Compute the refract dir in world space
               o.worldRefr = refract(-normalize(o.worldViewDir), normalize(o.worldNormal), _RefractRatio);

               TRANSFER_SHADOW(o);

               return o;
           }

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

               fixed3 ambient = UNITY_LIGHTMODEL_AMBIENT.xyz;

               fixed3 diffuse = _LightColor0.rgb * _Color.rgb * max(0, dot(worldNormal, worldLightDir));

               // Use the refract dir in world space to access the cubemap
               fixed3 refraction = texCUBE(_Cubemap, i.worldRefr).rgb * _RefractColor.rgb;

               UNITY_LIGHT_ATTENUATION(atten, i, i.worldPos);

               // Mix the diffuse color with the refract color
               fixed3 color = ambient + lerp(diffuse, refraction, _RefractAmount) * atten;

               return fixed4(color, 1.0);
           }

           ENDCG
       }
   }
   FallBack "Reflective/VertexLit"
}

取自《Unity Shader 入门精要》

_RefractRatio 为入射介质的折射/接收介质的折射率，比如空气折射率(1.0003)/水折射率(1.3333) = 0.7502

折射跟反射的区别是在refract函数最后一个参数传入折射率比例

材质折射率

真空 1.0000

空气 1.0003

冰 1.3090

水 1.3333

玻璃 1.5000

水晶 1.544～1.553

https://baike.baidu.com/item/%E5%B8%B8%E7%94%A8%E6%8A%98%E5%B0%84%E7%8E%87%E8%A1%A8/663686

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