BlueRoseNote/03-UnrealEngine/卡通渲染相关资料/渲染功能/ToonReflection&GI控制/Toon GI & Lumen.md

---
title: 未命名
date: 2025-03-27 17:37:02
excerpt: 
tags: 
rating: ⭐
---
# Toon Lumen
## 抹平法线思路
### ViewVector Fix WorldNormal
参考：
- [【UE5】环境光与GI 2：抹平法线](https://zhuanlan.zhihu.com/p/25839790454)

在`LumenScreenProbeGather.usf`中对法线进行抹平处理。其Pass位于
- DiffuseIndirectAndAO
	- LumenScreenProbeGather
		- Integrate
			- SimpleDiffuse/SupportImportanceSampleBRDF?/SupportAll?

在如下位置添加代码：
```c++
if (IsValid(Material))
	{
		const float2 ScreenUV = (Coord.SvPosition + 0.5f) * View.BufferSizeAndInvSize.zw;
		const float3 WorldPosition = GetWorldPositionFromScreenUV(ScreenUV, Material.SceneDepth);
		const float3 WorldNormal = Material.WorldNormal;
		//BlueRose Modify 
		if (Material.ShadingID == SHADINGMODELID_TOONSTANDARD)
		{
			//使用Yu-ki016的方法“抹平法线”
			float3 V = normalize(LWCHackToFloat(PrimaryView.WorldCameraOrigin) - WorldPosition);
			const uint ToonDataAssetID = GetToonDataAssetIDFromGBuffer(Material.GBufferData);
			float DiffuseIndirectLightingFlatten = GetDiffuseIndirectLightingFlatten(ToonDataAssetID);
			Material.WorldNormal = normalize(lerp(WorldNormal, V, DiffuseIndirectLightingFlatten));
		}
		//BlueRose Modify End
		...
	}
}
```

该方法存在一些问题：**当相机围绕角色旋转时，角色身上的 GI变化会比较明显**。

### 低频化WorldNormal & Spherical Harmonics
参考：
- [[UFSH2024]用虚幻引擎5为《幻塔》定制高品质动画流程风格化渲染管线 | 晨风 Neverwind 完美世界游戏】【精准空降到 12:55】](https://www.bilibili.com/video/BV1rW2LYvEox/?share_source=copy_web&vd_source=fe8142e8e12816535feaeabd6f6cdc8e&t=775)
- [[UFSH2024]用虚幻引擎5为《幻塔》定制高品质动画流程风格化渲染管线 | 晨风 Neverwind 完美世界游戏】 【精准空降到 36:52】](https://www.bilibili.com/video/BV1rW2LYvEox/?share_source=copy_web&vd_source=fe8142e8e12816535feaeabd6f6cdc8e&t=2212)
	- [ ] 需要实现：法线平滑 => 饱和度平滑。（没说细节，不清楚算法）
- [[UFSH2024]用虚幻引擎5为《幻塔》定制高品质动画流程风格化渲染管线 | 晨风 Neverwind 完美世界游戏】【精准空降到 35:09】](https://www.bilibili.com/video/BV1rW2LYvEox/?share_source=copy_web&vd_source=fe8142e8e12816535feaeabd6f6cdc8e&t=2109)
	- [ ] 小于等于High存储的是一个八面体，提前加一个Pass进行平滑：采样法线方向半球面的平均数值。
	- [ ] 大于等于Epic存储的是一个三阶球谐，保持1阶球谐数值不变，对2~3阶球谐按照系数进行平滑。并且添加能量补偿，大致与PBR的结果接近。
![[Lumen_SHData.png|800]]

![[Lumen_能量补偿1.png|800]]
![[Lumen_能量补偿2.png|800]]
UE5中采样球谐贴图方法(ReflectionEnvironmentShared.ush)：
```c++
/** 
 * Computes sky diffuse lighting from the SH irradiance map.  
 * This has the SH basis evaluation and diffuse convolution weights combined for minimal ALU's - see "Stupid Spherical Harmonics (SH) Tricks" 
 */
float3 GetSkySHDiffuse(float3 Normal)
{
	float4 NormalVector = float4(Normal, 1.0f); 

	float3 Intermediate0, Intermediate1, Intermediate2;
	Intermediate0.x = dot(SkyIrradianceEnvironmentMap[0], NormalVector);
	Intermediate0.y = dot(SkyIrradianceEnvironmentMap[1], NormalVector);
	Intermediate0.z = dot(SkyIrradianceEnvironmentMap[2], NormalVector);

	float4 vB = NormalVector.xyzz * NormalVector.yzzx;
	Intermediate1.x = dot(SkyIrradianceEnvironmentMap[3], vB);
	Intermediate1.y = dot(SkyIrradianceEnvironmentMap[4], vB);
	Intermediate1.z = dot(SkyIrradianceEnvironmentMap[5], vB);

	float vC = NormalVector.x * NormalVector.x - NormalVector.y * NormalVector.y;
	Intermediate2 = SkyIrradianceEnvironmentMap[6].xyz * vC;

	// max to not get negative colors
	return max(0, Intermediate0 + Intermediate1 + Intermediate2);
}
```

## Cel适配
需要实现Cel多光源方案。

大致的思路就是Copy Lumen结果，之后在[[Toon多光源参考|Toon多光源Pass]]中提取亮度，再根据亮度采样Ramp计算光影结果。