卡通材质

使用方式

在材质编辑器中添加Toon Shading节点，ShadingModel即切换为SHADINGMODELID_STYLIZED_SHADOW
注意：添加节点后不再受编辑器中的ShadingModel变量控制

How to use

Add Toon Shading node in material editor, and ShadingModel property will be replaced as toon shading model.

插件添加ShadingModel大致流程

注意该教程在引擎版本4.26时作成

继承UMaterialExpressionCustomOutput
使用虚幻中UMaterialExpressionCustomOutput类型可在代码编译时插入条件编译宏的特性将自定义的ShadingModelId添加进Shader编译流程
插件中重写的GetFunctionName返回的GetToonShading在shader对应的宏为NUM_MATERIAL_OUTPUTS_GETTOONSHADING
进入引擎Engine/Shader目录修改和添加Shader文件
修改ShadingCommon.ush中添加新的ShadingModel宏定义
- 添加宏SHADINGMODELID_STYLIZED_SHADOW，且修改SHADINGMODELID_NUM的数量（注意当前最多支持16个）
```
#define SHADINGMODELID_STYLIZED_SHADOW        12
#define SHADINGMODELID_NUM                    13
```
- 修改GetShadingModelColor函数，新增SHADINGMODELID_STYLIZED_SHADOW的调试颜色

修改BasePassCommon.ush与DeferredShadingCommon.ush开启自定义GBuffer的CustomData写入

BasePassCommon.ush WRITES_CUSTOMDATA_TO_GBUFFER宏，支持SHADINGMODELID_STYLIZED_SHADOW写入

#define WRITES_CUSTOMDATA_TO_GBUFFER        (USES_GBUFFER && (MATERIAL_SHADINGMODEL_SUBSURFACE || MATERIAL_SHADINGMODEL_PREINTEGRATED_SKIN || MATERIAL_SHADINGMODEL_SUBSURFACE_PROFILE || MATERIAL_SHADINGMODEL_CLEAR_COAT || MATERIAL_SHADINGMODEL_TWOSIDED_FOLIAGE || MATERIAL_SHADINGMODEL_HAIR || MATERIAL_SHADINGMODEL_CLOTH || MATERIAL_SHADINGMODEL_EYE || SHADINGMODELID_STYLIZED_SHADOW))

DeferredShadingCommon.ush 修改HasCustomGBufferData函数，支持SHADINGMODELID_STYLIZED_SHADOW写入

bool HasCustomGBufferData(int ShadingModelID)
{
  return ShadingModelID == SHADINGMODELID_SUBSURFACE
    || ShadingModelID == SHADINGMODELID_PREINTEGRATED_SKIN
    || ShadingModelID == SHADINGMODELID_CLEAR_COAT
    || ShadingModelID == SHADINGMODELID_SUBSURFACE_PROFILE
    || ShadingModelID == SHADINGMODELID_TWOSIDED_FOLIAGE
    || ShadingModelID == SHADINGMODELID_HAIR
    || ShadingModelID == SHADINGMODELID_CLOTH
    || ShadingModelID == SHADINGMODELID_EYE
    || ShadingModelID == SHADINGMODELID_STYLIZED_SHADOW;
}

修改BasePassPixelShader.usf中ShadingModel的初始化

#if NUM_MATERIAL_OUTPUTS_GETTOONSHADING
    uint ShadingModel = SHADINGMODELID_STYLIZED_SHADOW;
#else
    uint ShadingModel = GetMaterialShadingModel(PixelMaterialInputs);
#endif

修改ShadingModelsMaterial.ush将额外的数据写入GBuffer的CustomData

// 支持 MaterialExpressionCustomOutput 形式
#if NUM_MATERIAL_OUTPUTS_GETTOONSHADING
    else if (ShadingModel == SHADINGMODELID_STYLIZED_SHADOW)
    {
        GBuffer.CustomData.x = saturate( GetToonShading0(MaterialParameters) );  // SpecularRange
        GBuffer.CustomData.y = saturate( GetToonShading1(MaterialParameters) );  // Offset
    }
// 支持 ShadingModelId 形式
#elif SHADINGMODELID_STYLIZED_SHADOW
    else if (ShadingModel == SHADINGMODELID_STYLIZED_SHADOW)
    {
        GBuffer.CustomData.x = saturate( GetMaterialCustomData0(MaterialParameters) );  // SpecularRange
        GBuffer.CustomData.y = saturate( GetMaterialCustomData1(MaterialParameters) );  // Offset
    }
#endif

修改ShadingModels.ush支持添加的ShadingModel的自定义BxDF函数
IntegrateBxDF函数中添加SHADINGMODELID_STYLIZED_SHADOW的case
```
case SHADINGMODELID_STYLIZED_SHADOW:
   return StylizedShadowBxDF(GBuffer, N, V, L, Falloff, NoL, AreaLight, Shadow);
```

修改DeferredLightingCommon.ush自定义光照
修改GetDynamicLightingSplit函数，通过GBuffer.ShadingModelID判断SHADINGMODELID_STYLIZED_SHADOW执行自定义光照逻辑

// STYLIZEDSHADOW SHADING 
if (GBuffer.ShadingModelID == SHADINGMODELID_STYLIZED_SHADOW)
{
  float3 Attenuation = 1;

  float offset = GBuffer.CustomData.y;
  float TerminatorRange = saturate(GBuffer.Roughness - 0.5);
  
  offset = offset * 2 - 1;
  
  BRANCH
  if (offset >= 1)
  {
    Attenuation = 1;
  }
  else
  {
    float NoL = (dot(N, L) + 1) / 2;
    float NoLOffset = saturate(NoL + offset);
    float LightAttenuationOffset = saturate( Shadow.SurfaceShadow + offset);
    float ToonSurfaceShadow = smoothstep(0.5 - TerminatorRange, 0.5 + TerminatorRange, LightAttenuationOffset);

    Attenuation = smoothstep(0.5 - TerminatorRange, 0.5 + TerminatorRange, NoLOffset) * ToonSurfaceShadow;
  }

  LightAccumulator_AddSplit( LightAccumulator, Lighting.Diffuse, Lighting.Specular, Lighting.Diffuse, LightColor * LightMask * Shadow.SurfaceShadow * Attenuation * 0.25, > bNeedsSeparateSubsurfaceLightAccumulation);
}
else
{
  LightAccumulator_AddSplit( LightAccumulator, Lighting.Diffuse, Lighting.Specular, Lighting.Diffuse, LightColor * LightMask * Shadow.SurfaceShadow, bNeedsSeparateSubsurfaceLightAccumulation );
}

无法支持From Material Expression的原因

FMaterialShadingModelField::AddShadingModel 存在check(InShadingModel < MSM_NUM)检查导致没法Hack，导致新增的ShadingModel数量肯定超过MSM_NUM，引发断言导致编辑器crash

插件支持ShadingModel的方式