Unity Shader：實現菲涅爾+色散效果以及相關原理解析

Unity Shader：實現菲涅爾+色散效果以及相關原理解析

效果截圖

Shader源碼

Shader "Unlit/Dispersion"
{
    Properties {
        fresnelPower("fresnelPower",float)=0
        fresnelScale("fresnelScale",float)=0
        fresnelBias("fresnelBias",float)=0
        _r("r",float)=0
        _g("g",float)=0
        _b("b",float)=0

    }
    SubShader
    {
        Pass
        {
            CGPROGRAM
            #pragma vertex vert
            #pragma fragment frag
            #include "UnityCG.cginc"

            struct v2f {
                float3 normal:NORMAL;
                float3 worldRefra : TEXCOORD0;
                float4 pos : SV_POSITION;
                float4 objectPOS:float;
            };
            //在外部可改爲power=4,scale=0.1,bias=-0.2
            float fresnelPower=1.0f;
            float fresnelScale=1.0f;
            float fresnelBias=0.3f;
            //紅，綠，藍的折射率，從外部賦值，方便調整
            float3 etaRatio;// =float3(0.83f,0.67f,0.55f); //1/1.3 1/1.5 1/1.8
            float _r;
            float _g;
            float _b;
            v2f vert (float4 vertex : POSITION, float3 normal : NORMAL)
            {
                v2f o;
                o.pos = UnityObjectToClipPos(vertex);
                o.normal=normal;
                o.objectPOS=vertex;
                return o;
            }
            //爲了達到最佳效果，將所有計算都寫在了片段着色器內。
            fixed4 frag (v2f i) : SV_Target
            {

            etaRatio=float3(_r,_g,_b);

             i.normal = UnityObjectToWorldNormal(i.normal);
             float3 worldPos = mul(unity_ObjectToWorld, i.objectPOS).xyz;
             float3 worldViewDir = UnityWorldSpaceViewDir(worldPos);
            //反射向量
             float R=reflect(-worldViewDir,i.normal);

             i.normal=normalize(i.normal);
            //計算用來模擬色散的折射向量
             float3 Tred=refract(normalize(-worldViewDir),i.normal,etaRatio.x);
             float3 Tgreen=refract(normalize(-worldViewDir),i.normal,etaRatio.y);
             float3 Tblue=refract(normalize(-worldViewDir),i.normal,etaRatio.z);
            //菲涅爾factor，用來混合反射與折射顏色。
             float reflectionfactor=min(1.0f,max(0,fresnelBias+fresnelScale*pow(1.0f+dot(normalize(-worldViewDir),i.normal),fresnelPower)));
            //如果利用color存此變量，可以省去min與max。
        //     color reflectionfactor=fresnelBias+fresnelScale*pow(1.0f+dot(normalize(-worldViewDir),i.normal),fresnelPower);

             half4 skyData = UNITY_SAMPLE_TEXCUBE(unity_SpecCube0, R);
             //反射顏色
             float4 reflectedColor=half4(DecodeHDR (skyData, unity_SpecCube0_HDR),1.0f);

             float4 refractedColor;
             //折射顏色
             refractedColor.r=DecodeHDR (UNITY_SAMPLE_TEXCUBE(unity_SpecCube0, Tred),unity_SpecCube0_HDR).r;
             refractedColor.g=DecodeHDR (UNITY_SAMPLE_TEXCUBE(unity_SpecCube0, Tgreen),unity_SpecCube0_HDR).g;
             refractedColor.b=DecodeHDR (UNITY_SAMPLE_TEXCUBE(unity_SpecCube0, Tblue),unity_SpecCube0_HDR).b;
             refractedColor.a=1.0f;
             fixed4 c=0;
             //混合
             c=lerp(refractedColor,reflectedColor,reflectionfactor.x);
             return c;

            }
            ENDCG
        }
    }
}