UE5.8 Substrate Toon Shading

1. 管道分层（6 Layers）

2. BSDF 类型注册

Substrate 框架在 SubstrateDefinitions.h 中定义所有 BSDF 类型。Toon BSDF 注册为常量 SUBSTRATE_BSDF_TYPE_TOON = 6。

#define SUBSTRATE_BSDF_TYPE_SLAB                0
#define SUBSTRATE_BSDF_TYPE_VOLUMETRICFOGCLOUD  1
#define SUBSTRATE_BSDF_TYPE_UNLIT               2
#define SUBSTRATE_BSDF_TYPE_HAIR                3
#define SUBSTRATE_BSDF_TYPE_SINGLELAYERWATER   4
#define SUBSTRATE_BSDF_TYPE_EYE                 5
#define SUBSTRATE_BSDF_TYPE_TOON                6  // ← Toon BSDF

3. Shader 入口 — SubstrateToonBSDF.ush

uint PackToonCustomData(in float2 UVs, in float ProfileId, in float Dither)
{
    uint U12bits = saturate(UVs.x) * 4095.0f;
    uint V12bits = saturate(UVs.y) * 4095.0f;
    uint Packed  = U12bits;
    Packed |= V12bits << 12;
    Packed |= (uint(ProfileId) & 0xFF) << 24;
    return Packed;
}

struct FSubstrateEvaluateToonResult {
    float3 IntegratedDiffuseValue;
    float3 IntegratedSpecularValue;
    float3 DiffuseColor;
    float3 EmissivePathValue;
    float3 DiffusePathValue;
    float3 SpecularPathValue;
    float  DiffusePDF;
    float3 ThroughputV;
    float3 TransmittanceAlongN;
    bool   bPostProcessSubsurface;
    float  ToonDataWeight;
    float  ToonDataShadowNoL;
};

4. 评估调度流程

三种路径（Forward / Deferred / Mobile）汇聚到同一入口，最终从 L6 的 3D ToonProfile Atlas 采样漫反射 Ramp、镜面反射和阴影排线。

5. 移动端约束

#define TOON_CAN_USE_PATTERNS_UVS \
  (!SHADING_PATH_MOBILE || \
   (!MOBILE_DEFERRED_SHADING || MOBILE_EXTENDED_GBUFFER))

6. Console Variables

7. 源文件索引

8. BSDF 注册链路