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前言

Unity中Shader的Standard材质解析（二），对 Standard 的 PBR 的 GI 进行解析

• Unity中Shader的Standard材质解析（一）

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一、我们对 Standard 的 PBR 的 GI 进行解析

1、我们先创建一个PBR的.cginc文件，用于整理用到的函数

2、然后在Standard的Shader中引用该cginc文件

#include “CGInclude/MyPhysicallyBasedRendering.cginc”

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二、依次整理函数到该cginc文件中

• 整理 LightingStandard_GI1(o, giInput, gi); 中的数据

• Unity_GlossyEnvironmentData表示GI中的反射准备数据

• 准备好反射数据后，计算得出GI中的 漫反射 和 镜面反射

• 输出漫反射看看效果

• 输出镜面反射看看效果

• 我们可以自定义一下Cubemap,看看不同的反射效果

（这就是PBR的优点，可以根据不同的环境，直接呈现效果，不用再根据环境调节参数）

我们来看一下PBR中GI的镜面反射做了些什么

• 这个程序块只会在，反射探针中开启Box Projection时，才会运行

这选项的作用是：使用反射探针的物体在移动时，效果不会变，只有在摄像机方向变时，效果才会变化。那么，要让物体动时，反射效果同时改变的话，就需要开启该选项。

• 在取消了材质的Reflection后，会运行该程序块
• 反之，运行之后的部分

• 在开启反射效果后，对于感性粗糙度的计算。
• 在Unity中的粗糙度，使用分级贴图来模拟粗糙度（节省性能）

• 由于粗糙度与反射探针的mip变化不呈现线性正比，所以需要一个公式来改变

//r = r * (1.7 - 0.7r)
perceptualRoughness = perceptualRoughness(1.7 - 0.7*perceptualRoughness);

在Blender中，粗糙度是按数值改变的：

在Unity中，粗糙度是按贴图分级来模拟的粗糙度：

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二、最终代码

.cginc代码：

#ifndef MYPHYSICALLYBASERENDERING_INCLUDE
    #define MYPHYSICALLYBASERENDERING_INCLUDE

    half3 Unity_GlossyEnvironment1 (UNITY_ARGS_TEXCUBE(tex), half4 hdr, Unity_GlossyEnvironmentData glossIn)
    {
        half perceptualRoughness = glossIn.roughness /* perceptualRoughness */ ;

        // TODO: CAUTION: remap from Morten may work only with offline convolution, see impact with runtime convolution!
        // For now disabled
        #if 0
        float m = PerceptualRoughnessToRoughness(perceptualRoughness); // m is the real roughness parameter
        const float fEps = 1.192092896e-07F;        // smallest such that 1.0+FLT_EPSILON != 1.0  (+1e-4h is NOT good here. is visibly very wrong)
        float n =  (2.0/max(fEps, m*m))-2.0;        // remap to spec power. See eq. 21 in --> https://dl.dropboxusercontent.com/u/55891920/papers/mm_brdf.pdf

        n /= 4;                                     // remap from n_dot_h formulatino to n_dot_r. See section "Pre-convolved Cube Maps vs Path Tracers" --> https://s3.amazonaws.com/docs.knaldtech.com/knald/1.0.0/lys_power_drops.html

        perceptualRoughness = pow( 2/(n+2), 0.25);      // remap back to square root of real roughness (0.25 include both the sqrt root of the conversion and sqrt for going from roughness to perceptualRoughness)
        #else
        // MM: came up with a surprisingly close approximation to what the #if 0'ed out code above does.
        //r = r * (1.7 - 0.7*r)
        //由于粗糙度与反射探针的mip变化不呈现线性正比，所以需要一个公式来改变
        perceptualRoughness = perceptualRoughness*(1.7 - 0.7*perceptualRoughness);
        #endif

        //UNITY_SPECCUBE_LOD_STEPS = 6,表示反射探针的mip级别有 6 档。粗糙度X6得到最终得mip级别
        half mip = perceptualRoughnessToMipmapLevel(perceptualRoughness);
        half3 R = glossIn.reflUVW;
        half4 rgbm = UNITY_SAMPLE_TEXCUBE_LOD(tex, R, mip);

        return DecodeHDR(rgbm, hdr);
    }



    //GI中的镜面反射
    inline half3 UnityGI_IndirectSpecular1(UnityGIInput data, half occlusion, Unity_GlossyEnvironmentData glossIn)
    {
        half3 specular;
        //如果开启了反射探针的Box Projection
        #ifdef UNITY_SPECCUBE_BOX_PROJECTION
        // we will tweak reflUVW in glossIn directly (as we pass it to Unity_GlossyEnvironment twice for probe0 and probe1), so keep original to pass into BoxProjectedCubemapDirection
        half3 originalReflUVW = glossIn.reflUVW;
        glossIn.reflUVW = BoxProjectedCubemapDirection (originalReflUVW, data.worldPos, data.probePosition[0], data.boxMin[0], data.boxMax[0]);
        #endif

        #ifdef _GLOSSYREFLECTIONS_OFF
        specular = unity_IndirectSpecColor.rgb;
        #else
        half3 env0 = Unity_GlossyEnvironment1 (UNITY_PASS_TEXCUBE(unity_SpecCube0), data.probeHDR[0], glossIn);
        //如果开启了反射探针混合
        #ifdef UNITY_SPECCUBE_BLENDING
        const float kBlendFactor = 0.99999;
        float blendLerp = data.boxMin[0].w;
        UNITY_BRANCH
        if (blendLerp < kBlendFactor)
        {
            #ifdef UNITY_SPECCUBE_BOX_PROJECTION
            glossIn.reflUVW = BoxProjectedCubemapDirection (originalReflUVW, data.worldPos, data.probePosition[1], data.boxMin[1], data.boxMax[1]);
            #endif

            half3 env1 = Unity_GlossyEnvironment (UNITY_PASS_TEXCUBE_SAMPLER(unity_SpecCube1,unity_SpecCube0), data.probeHDR[1], glossIn);
            specular = lerp(env1, env0, blendLerp);
        }
        else
        {
            specular = env0;
        }
        #else
        specular = env0;
        #endif
        #endif

        return specular * occlusion;
    }


    inline UnityGI UnityGlobalIllumination1 (UnityGIInput data, half occlusion, half3 normalWorld)
    {
        return UnityGI_Base(data, occlusion, normalWorld);
    }
    //GI计算
    inline UnityGI UnityGlobalIllumination1 (UnityGIInput data, half occlusion, half3 normalWorld, Unity_GlossyEnvironmentData glossIn)
    {
        //计算得出GI中的漫反射
        UnityGI o_gi = UnityGI_Base(data, occlusion, normalWorld);
        //计算得出GI中的镜面反射
        o_gi.indirect.specular = UnityGI_IndirectSpecular1(data, occlusion, glossIn);
        return o_gi;
    }
    float SmoothnessToPerceptualRoughness1(float smoothness)
    {
        return (1 - smoothness);
    }
    Unity_GlossyEnvironmentData UnityGlossyEnvironmentSetup1(half Smoothness, half3 worldViewDir, half3 Normal, half3 fresnel0)
    {
        Unity_GlossyEnvironmentData g;
        //粗糙度
        g.roughness /* perceptualRoughness */   = SmoothnessToPerceptualRoughness1(Smoothness);
        //反射球的采样坐标
        g.reflUVW   = reflect(-worldViewDir, Normal);

        return g;
    }

    //PBR光照模型的GI计算
    inline void LightingStandard_GI1(
        SurfaceOutputStandard s,
        UnityGIInput data,
        inout UnityGI gi)
    {
        //如果是延迟渲染PASS并且开启了延迟渲染反射探针的话
        #if defined(UNITY_PASS_DEFERRED) && UNITY_ENABLE_REFLECTION_BUFFERS
        gi = UnityGlobalIllumination1(data, s.Occlusion, s.Normal);
        #else

        //Unity_GlossyEnvironmentData表示GI中的反射准备数据
        Unity_GlossyEnvironmentData g = UnityGlossyEnvironmentSetup1(s.Smoothness, data.worldViewDir, s.Normal,
                                                                    lerp(unity_ColorSpaceDielectricSpec.rgb, s.Albedo,
                                                                         s.Metallic));
        //进行GI计算并返回输出gi
        gi = UnityGlobalIllumination1(data, s.Occlusion, s.Normal, g);
        #endif
    }


#endif

Shader代码：

//Standard材质
Shader "MyShader/P2_2_5"
{
    Properties
    {
        _Color ("Color", Color) = (1,1,1,1)
        _MainTex ("Albedo (RGB)", 2D) = "white" {}
        [NoScaleOffset]_MetallicTex("Metallic(R) Smoothness(G) AO(B)",2D) = "white" {}
        [NoScaleOffset][Normal]_NormalTex("NormalTex",2D) = "bump" {}
        
        _Glossiness ("Smoothness", Range(0,1)) = 0.0
        _Metallic ("Metallic", Range(0,1)) = 0.0
        _AO("AO",Range(0,1)) = 1.0
    }
    SubShader
    {
        Tags
        {
            "RenderType"="Opaque"
        }
        LOD 200

        // ---- forward rendering base pass:
        Pass
        {
            Name "FORWARD"
            Tags
            {
                "LightMode" = "ForwardBase"
            }

            CGPROGRAM
            // compile directives
            #pragma vertex vert
            #pragma fragment frag
            #pragma target 3.0
            #pragma multi_compile_instancing
            #pragma multi_compile_fog
            #pragma multi_compile_fwdbase

            #include "UnityCG.cginc"
            #include "Lighting.cginc"
            #include "UnityPBSLighting.cginc"
            #include "AutoLight.cginc"
            #include "CGInclude/MyPhysicallyBasedRendering.cginc"
                
            sampler2D _MainTex;
            float4 _MainTex_ST;
            half _Glossiness;
            half _Metallic;
            fixed4 _Color;
            sampler2D _MetallicTex;
            half _AO;
            sampler2D _NormalTex;
            
            struct appdata
            {
                float4 vertex : POSITION;
                float4 tangent : TANGENT;
                float3 normal : NORMAL;
                float4 texcoord : TEXCOORD0;
                float4 texcoord1 : TEXCOORD1;
                float4 texcoord2 : TEXCOORD2;
                float4 texcoord3 : TEXCOORD3;
                fixed4 color : COLOR;
                UNITY_VERTEX_INPUT_INSTANCE_ID
            };

            // vertex-to-fragment interpolation data
            // no lightmaps:
            struct v2f
            {
                float4 pos : SV_POSITION;
                float2 uv : TEXCOORD0; // _MainTex
                float3 worldNormal : TEXCOORD1;
                float3 worldPos : TEXCOORD2;
                #if UNITY_SHOULD_SAMPLE_SH
                    half3 sh : TEXCOORD3; // SH
                #endif
                //切线空间需要使用的矩阵
                float3 tSpace0 : TEXCOORD4;
                float3 tSpace1 : TEXCOORD5;
                float3 tSpace2 : TEXCOORD6;

                UNITY_FOG_COORDS(7)
                UNITY_SHADOW_COORDS(8)
            };

            // vertex shader
            v2f vert(appdata v)
            {
                v2f o;

                o.pos = UnityObjectToClipPos(v.vertex);
                o.uv.xy = TRANSFORM_TEX(v.texcoord, _MainTex);
                float3 worldPos = mul(unity_ObjectToWorld, v.vertex).xyz;
                float3 worldNormal = UnityObjectToWorldNormal(v.normal);

                //世界空间下的切线
                half3 worldTangent = UnityObjectToWorldDir(v.tangent);
                //切线方向
                half tangentSign = v.tangent.w * unity_WorldTransformParams.w;
                //世界空间下的副切线
                half3 worldBinormal = cross(worldNormal, worldTangent) * tangentSign;
                //切线矩阵
                o.tSpace0 = float3(worldTangent.x, worldBinormal.x, worldNormal.x);
                o.tSpace1 = float3(worldTangent.y, worldBinormal.y, worldNormal.y);
                o.tSpace2 = float3(worldTangent.z, worldBinormal.z, worldNormal.z);

                o.worldPos.xyz = worldPos;
                o.worldNormal = worldNormal;

                // SH/ambient and vertex lights

                #if UNITY_SHOULD_SAMPLE_SH && !UNITY_SAMPLE_FULL_SH_PER_PIXEL
                    o.sh = 0;
                    // Approximated illumination from non-important point lights
                #ifdef VERTEXLIGHT_ON
                    o.sh += Shade4PointLights (
                    unity_4LightPosX0, unity_4LightPosY0, unity_4LightPosZ0,
                    unity_LightColor[0].rgb, unity_LightColor[1].rgb, unity_LightColor[2].rgb, unity_LightColor[3].rgb,
                    unity_4LightAtten0, worldPos, worldNormal);
                #endif
                    o.sh = ShadeSHPerVertex (worldNormal, o.sh);
                #endif


                UNITY_TRANSFER_LIGHTING(o, v.texcoord1.xy);

                UNITY_TRANSFER_FOG(o, o.pos); // pass fog coordinates to pixel shader

                return o;
            }

            // fragment shader
            fixed4 frag(v2f i) : SV_Target
            {
                UNITY_EXTRACT_FOG(i);
                
                float3 worldPos = i.worldPos.xyz;
                
                float3 worldViewDir = normalize(UnityWorldSpaceViewDir(worldPos));

                SurfaceOutputStandard o;
                UNITY_INITIALIZE_OUTPUT(SurfaceOutputStandard, o);

                fixed4 mainTex = tex2D(_MainTex, i.uv);
                o.Albedo = mainTex.rgb * _Color;

                o.Emission = 0.0;

                fixed4 metallicTex = tex2D(_MetallicTex, i.uv);
                o.Metallic = metallicTex.r * _Metallic;
                o.Smoothness = metallicTex.g * _Glossiness;
                o.Occlusion = metallicTex.b * _AO;
                o.Alpha = 1;


                half3 normalTex = UnpackNormal(tex2D(_NormalTex,i.uv));
                half3 worldNormal = half3(dot(i.tSpace0,normalTex),dot(i.tSpace1,normalTex),dot(i.tSpace2,normalTex));
                o.Normal = worldNormal;


                // compute lighting & shadowing factor
                UNITY_LIGHT_ATTENUATION(atten, i, worldPos)

                // Setup lighting environment
                UnityGI gi;
                UNITY_INITIALIZE_OUTPUT(UnityGI, gi);
                gi.indirect.diffuse = 0;
                gi.indirect.specular = 0;
                gi.light.color = _LightColor0.rgb;
                gi.light.dir = _WorldSpaceLightPos0.xyz;
                // Call GI (lightmaps/SH/reflections) lighting function
                UnityGIInput giInput;
                UNITY_INITIALIZE_OUTPUT(UnityGIInput, giInput);
                giInput.light = gi.light;
                giInput.worldPos = worldPos;
                giInput.worldViewDir = worldViewDir;
                giInput.atten = atten;
                #if defined(LIGHTMAP_ON) || defined(DYNAMICLIGHTMAP_ON)
                    giInput.lightmapUV = IN.lmap;
                #else
                giInput.lightmapUV = 0.0;
                #endif
                #if UNITY_SHOULD_SAMPLE_SH && !UNITY_SAMPLE_FULL_SH_PER_PIXEL
                    giInput.ambient = i.sh;
                #else
                giInput.ambient.rgb = 0.0;
                #endif
                giInput.probeHDR[0] = unity_SpecCube0_HDR;
                giInput.probeHDR[1] = unity_SpecCube1_HDR;
                #if defined(UNITY_SPECCUBE_BLENDING) || defined(UNITY_SPECCUBE_BOX_PROJECTION)
                    giInput.boxMin[0] = unity_SpecCube0_BoxMin; // .w holds lerp value for blending
                #endif
                #ifdef UNITY_SPECCUBE_BOX_PROJECTION
                    giInput.boxMax[0] = unity_SpecCube0_BoxMax;
                    giInput.probePosition[0] = unity_SpecCube0_ProbePosition;
                    giInput.boxMax[1] = unity_SpecCube1_BoxMax;
                    giInput.boxMin[1] = unity_SpecCube1_BoxMin;
                    giInput.probePosition[1] = unity_SpecCube1_ProbePosition;
                #endif
                
                LightingStandard_GI1(o, giInput, gi);
                
                //return fixed4(gi.indirect.specular,1);
                
                // PBS的核心计算
                fixed4 c = LightingStandard(o, worldViewDir, gi);
                
                UNITY_APPLY_FOG(_unity_fogCoord, c); // apply fog
                UNITY_OPAQUE_ALPHA(c.a); //把c的Alpha置1
                return c;
            }
            ENDCG

        }
    }

}