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）
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”
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，反射探针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
}
}
}
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