PBR Material SystemPBR 材质系统

Material Architecture — Two Authoring Paths材质架构 — 两种创作路径

NeoX materials exist in two forms. The handwritten path uses a clean set of Get*() interface functions in material.hlsl. The material-graph path produces a compiled default.hlsl where all parameters are resolved in one monolithic CalcMaterialParam() call. Both paths feed the same downstream pipeline.

NeoX 材质有两种形式。手写路径在 material.hlsl 中使用一组整洁的 Get*() 接口函数。材质图路径产生编译后的 default.hlsl，所有参数在单个 CalcMaterialParam() 调用中解析。两种路径都向同一下游管线输出。

Texture Slot Convention — The MRO Pack纹理槽位约定 — MRO 打包

All standard PBR materials follow a fixed 4-texture, 3-slot encoding. The third texture packs three physically-based parameters into RGB channels — called MRO (Metalness, Roughness, Occlusion):

所有标准 PBR 材质遵循固定的 4 纹理、3 槽位编码。第三张纹理将三个基于物理的参数打包到 RGB 通道中——称为 MRO（金属度、粗糙度、遮蔽）：

* The Alpha channel of Tex2 has material-specific meaning: for skin it carries SSS curvature; for the 4S SSSS material it carries SSS blur intensity; for terrain it may carry blend weights.

* Tex2 的 Alpha 通道有材质特定含义：皮肤材质存储 SSS 曲率；4S SSSS 材质存储 SSS 模糊强度；地形材质可能存储混合权重。

Material Interface Functions材质接口函数

Every material file implements the same set of interface functions. The engine's SetupMaterial() calls them in order to fill the Material struct:

每个材质文件实现同一套接口函数。引擎的 SetupMaterial() 按顺序调用它们以填充 Material 结构体：

// material.hlsl — Normal decoding (standard TBN path)
void GetNormal(Fragment frag, RawData raw, inout Material mtl) {
#if LIGHT_ENABLE && NORMAL_MAP_ENABLE
  float3 n = raw.tex1.xyz * 2.0 - 1.0;
  n.xy *= Intensity.x;          // normal intensity
  float3x3 TBN = float3x3(frag.tangent_world,
                             frag.binormal_world,
                             frag.normal_world);
  mtl.normal = normalize(mul(n, TBN));
#else
  mtl.normal = frag.normal_world;
#endif
}

// material_ssss.hlsl — UE4 normal path (z reconstruction)
void GetNormal(...) {
#if IMPORT_FROM_UE4
  n.z = sqrt(max(1.0 - dot(n.xy, n.xy), 0));  // reconstruct Z
#endif
  // ... rest of TBN decode
}

default.hlsl — Material Graph Compiled Shaderdefault.hlsl — 材质图编译着色器

The new engine's default.hlsl is the output of the material graph editor — rather than separate Get*() functions, all parameter logic is centralized in a single CalcMaterialParam() function. This enables features impossible in the handwritten path:

新引擎的 default.hlsl 是材质图编辑器的输出——所有参数逻辑集中在单个 CalcMaterialParam() 函数中，而非独立的 Get*() 函数。这使得手写路径无法实现的功能成为可能：

// default.hlsl — Emissive with EMISSIVE_TEXTURE macro
float3 emissive_color;
#if EMISSIVE_TEXTURE
  emissive_color = GetColorTextureValue(Tex3, s3, uv0) * EmissiveColor.rgb * Intensity.w;
#else
  emissive_color = tex2.a * albedo_color * EmissiveColor.rgb;  // tex2.a carries emissive mask
#endif

// Refraction path — depth-aware UV distortion
#if SHADER_REFRACTION
  float2 refract_uv = screen_uv + normal.xy * RefractionStrength;
  float refract_depth = SampleDepth(mgDepthBufferSampler, refract_uv);
  // fall back to unrefracted if behind surface
  refract_uv = refract_depth > input_depth ? refract_uv : screen_uv;
#endif

Specialized Material Types专用材质类型

material_skin.hlsl — Pre-Integrated Skinmaterial_skin.hlsl — 预积分皮肤

Adds two LUT textures for pre-integrated skin shading. Metalness is hardcoded to 0 (skin is always dielectric). The key additions are the LUT samplers and SSS curvature readback:

为预积分皮肤着色添加两张 LUT 纹理。金属度硬编码为 0（皮肤始终是电介质）。关键增加是 LUT 采样器和 SSS 曲率回读：

// Additional textures: t3 = pre-integrated LUT, t4 = shadow color LUT
Texture2D Tex3 : register(t3);  // sampled at (0.5*NoL+0.5, curvature)
Texture2D Tex4 : register(t4);  // sampled at (shadow, curvature)
SamplerState s1;                 // Trilinear_Clamp for LUTs

float  GetSSSCurvature(...) { return 1.0 - raw.tex2.b; } // inverted metalness channel
float3 GetRawPreintergratedSkin(float2 uv) { return Tex3.Sample(s1, uv).rgb; }
float3 GetRawSkinShadowColor(float2 uv)    { return Tex4.Sample(s1, uv).rgb; }

material_hair.hlsl — Anisotropic Flow Mapmaterial_hair.hlsl — 各向异性流向图

Uses a 4th texture as a hair flow map (Tex3) that encodes the tangent direction along hair strands. The flow map drives the anisotropic tangent stored in mtl.tangent:

使用第 4 张纹理作为发丝流向图（Tex3），编码沿发丝方向的切线方向。流向图驱动存储在 mtl.tangent 中的各向异性切线：

// Tex3.xy = flow direction in [0,1] → [-1,1]
// Tex3.z  = blend weight between flow normal and geometric normal
float3 flow = raw.tex3.xy * 2.0 - 1.0;
float3 flow_tangent = normalize(mul(float3(flow, 0), TBN));
float3 final_tangent = normalize(flow_tangent + raw.tex3.z * Intensity.w * world_normal);
mtl.tangent = final_tangent;
// Hack: stash original world normal in sss_color for the hair shading model
mtl.sss_color = original_world_normal;

material_toon.hlsl — Toon Step Parametersmaterial_toon.hlsl — 卡通阶梯参数

Toon materials hijack the sss_color field to pass step-function parameters to the toon.hlsl shading model. This avoids adding new fields to the Material struct:

卡通材质借用 sss_color 字段向 toon.hlsl 着色模型传递阶梯函数参数。这避免了向 Material 结构体添加新字段：

// Uniforms: toon_threshold, toon_range (the Lerp3 breakpoints)
void GetSSSColor(...) {
  mtl.sss_color = float3(toon_threshold, toon_range, 0);  // packed as color
}
// GetEmissive() uses albedo * intensity (glow from base color)
mtl.emissive = mtl.albedo * Intensity.w * EmissiveColor.rgb;

material_ssss.hlsl — 4S Dual-Lobe SSSmaterial_ssss.hlsl — 4S 双波瓣次表面散射

The most parameter-rich material, supporting dual-lobe specular (for realistic skin highlight splitting) and physically-based SSS transmittance. Key extra uniforms:

参数最丰富的材质，支持双波瓣高光（实现真实皮肤高光分裂）和基于物理的 SSS 透射。关键额外 Uniform：

Material File Map材质文件地图

• materials/material_common.hlslSingle helper: MakeMaterialRoughness() = saturate(r); defines NEOX_IS_IGL default单一辅助函数：MakeMaterialRoughness()；定义 NEOX_IS_IGL 默认值
• materials/material.hlslHandwritten standard PBR — 3 textures, separate Get*() functions手写标准 PBR — 3 张纹理，独立 Get*() 函数
• ../default.hlsl + default.surfMaterial-graph compiled PBR — monolithic CalcMaterialParam(), 4 textures, macro features材质图编译 PBR — 单体 CalcMaterialParam()，4 张纹理，宏功能
• materials/material_skin.hlslPre-integrated skin — 5 textures (adds 2D LUTs for subsurface), metalness = 0预积分皮肤 — 5 张纹理（添加次表面 2D LUT），金属度=0
• materials/material_hair.hlslAnisotropic Marschner hair — 4 textures (adds flow map), custom tangent pipeline各向异性 Marschner 头发 — 4 张纹理（添加流向图），自定义切线管线
• materials/material_toon.hlslToon/cel-shaded — packs step params into sss_color; includes toonedge_helper.hlsl卡通着色 — 将阶梯参数打包到 sss_color；包含 toonedge_helper.hlsl
• materials/material_toonedge.hlslSilhouette outline pass — vertex extrusion along normal by SilhouetteEdgeWidth轮廓描边 Pass — 沿法线按 SilhouetteEdgeWidth 挤出顶点
• materials/material_ssss.hlsl4S separable SSS — dual-lobe spec, FalloffColor, TransmissionParams, UE4 normal import4S 可分离 SSS — 双波瓣高光，衰减颜色，透射参数，UE4 法线导入
• materials/material_subsurface.hlslSimple single-sided SSS — curvature from tex2.a, color derived from albedo简单单面 SSS — 从 tex2.a 读取曲率，颜色从反照率导出
• materials/material_multi_layered_pbr.hlsl1-coat layered PBR — 5 textures (+FGD LUT t4, coat normal t5)1 涂层分层 PBR — 5 张纹理（+FGD LUT t4，涂层法线 t5）
• materials/material_multi_layered_pbr2.hlsl2-coat layered PBR — 6 textures (+2 coat normals t5-t6)2 涂层分层 PBR — 6 张纹理（+2 涂层法线 t5-t6）
• materials/material_multi_layered_pbr3.hlsl3-coat layered PBR — 7 textures (+3 coat normals t5-t7)3 涂层分层 PBR — 7 张纹理（+3 涂层法线 t5-t7）
• materials/material_terrain.hlslTerrain blend material — multi-layer splat mapping地形混合材质 — 多层溅射贴图
• materials/material_glint.hlslGlint material setup — feeds GlintDictionary texture and slope-space params to glint.hlsl闪光材质设置 — 向 glint.hlsl 提供 GlintDictionary 纹理和斜率空间参数