131 lines
3.9 KiB
Markdown
131 lines
3.9 KiB
Markdown
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---
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title: RED自定义数据通道
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date: 2026-05-03 00:00:00
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excerpt: 复用 GBuffer CustomData 通道存储轮廓线 ID 和点光源 DiffuseColor
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tags:
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- ARC
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- Rendering
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- GBuffer
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- Toon
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rating: ⭐
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---
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# RED 自定义数据通道
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返回 [[Rendering]]
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## 概述
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RED 自定义数据通道是 ARC 引擎中一个巧妙的 GBuffer 复用方案。它将 UE4 原有的 **Subsurface Scattering** 数据通道（GBufferD CustomData）重新用于存储卡通渲染所需的**轮廓线 ID** 和**点光源 DiffuseColor**，避免了新增 GBuffer 通道带来的带宽开销。
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## 控制宏
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```hlsl
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// Definitions.usf
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#ifndef USE_RED_CUSTOM_DATA_POINTLIGHT
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#define USE_RED_CUSTOM_DATA_POINTLIGHT 0
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#endif
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#ifndef USE_RED_CUSTOM_DATA
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#define USE_RED_CUSTOM_DATA USE_RED_CUSTOM_DATA_POINTLIGHT
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#endif
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```
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两个模式：
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- `USE_RED_CUSTOM_DATA` — 基础模式，存储轮廓线 ID（从 SubsurfaceData.b 通道读取）
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- `USE_RED_CUSTOM_DATA_POINTLIGHT` — 点光源模式，存储 Emissive 作为 DiffuseColor
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## 数据写入流程
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### 1. 启用 CustomData 写入
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在 `BasePassCommon.ush` 中，将 `USE_RED_CUSTOM_DATA` 加入 `WRITES_CUSTOMDATA_TO_GBUFFER` 条件：
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```hlsl
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#define WRITES_CUSTOMDATA_TO_GBUFFER (USES_GBUFFER && (
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MATERIAL_SHADINGMODEL_SUBSURFACE ||
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MATERIAL_SHADINGMODEL_SUBSURFACE_PROFILE ||
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... ||
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USE_RED_CUSTOM_DATA ))
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```
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### 2. 填充 CustomData
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在 `ShadingModelsMaterial.ush` 中，为 `UNLIT` 和 `DEFAULT_LIT` 两个 ShadingModel 注入自定义数据：
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```hlsl
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#if MATERIAL_SHADINGMODEL_UNLIT
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GBuffer.ShadingModelID = SHADINGMODELID_UNLIT;
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#if USE_RED_CUSTOM_DATA
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GBuffer.CustomData = float4(SubsurfaceColor, SubsurfaceProfile);
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#endif
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#elif MATERIAL_SHADINGMODEL_DEFAULT_LIT
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GBuffer.ShadingModelID = SHADINGMODELID_DEFAULT_LIT;
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#if USE_RED_CUSTOM_DATA
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GBuffer.CustomData = float4(SubsurfaceColor, SubsurfaceProfile);
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#endif
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#endif
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```
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### 3. SubsurfaceColor 的实际含义
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在 `BasePassPixelShader.usf` 中，SubsurfaceColor 被重新赋值：
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```hlsl
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#if USE_RED_CUSTOM_DATA
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{
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#if USE_RED_CUSTOM_DATA_POINTLIGHT
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// 点光源模式：Emissive 作为 DiffuseColor
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SubsurfaceColor = Emissive;
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SubsurfaceProfile = 0.0;
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#else
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// 基础模式：B 通道存储 OutlineID
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float4 SubsurfaceData = GetMaterialSubsurfaceData(PixelMaterialInputs);
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SubsurfaceColor = float3(0, 0, 0);
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SubsurfaceProfile = SubsurfaceData.b; // OutlineID
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#endif
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}
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#endif
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```
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### 4. 写入 GBufferD
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在 `DeferredShadingCommon.ush` 中：
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```hlsl
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#if USE_RED_CUSTOM_DATA
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OutGBufferD = GBuffer.CustomData;
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#endif
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```
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## 数据读取
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- **轮廓线渲染**：从 GBufferD.b 读取 OutlineID，用于区分不同物体的轮廓线参数
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- **点光源着色**：从 GBufferD.rgb 读取 DiffuseColor，用于 [[RED阴影系统]] 的阴影着色
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- **角色辉光**：[[自定义后处理]] 中的 CharaGlow 读取 GBufferD.b 作为辉光遮罩
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## 设计权衡
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| 优点 | 缺点 |
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|------|------|
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| 零额外 GBuffer 带宽开销 | 无法同时使用 SSS 材质 |
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| 复用已有的 CustomData 管线 | UNLIT/DEFAULT_LIT 的 SubsurfaceColor 被占用 |
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| 对渲染管线入侵性小 | 两种模式（基础/点光源）互斥 |
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## 关联文档
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- [[RED阴影系统]] — 点光源模式下 DiffuseColor 的使用方
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- [[自定义后处理]] — CharaGlow 读取 OutlineID 通道
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- [[GBuffer修改]] — GBufferD 清除色等相关修改
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## 修改文件列表
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| 文件 | 修改类型 |
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|------|---------|
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| `Shaders/Private/Definitions.usf` | 新增 `USE_RED_CUSTOM_DATA` 宏定义 |
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| `Shaders/Private/BasePassCommon.ush` | 扩展 `WRITES_CUSTOMDATA_TO_GBUFFER` |
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| `Shaders/Private/ShadingModelsMaterial.ush` | UNLIT/DEFAULT_LIT 写入 CustomData |
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| `Shaders/Private/BasePassPixelShader.usf` | SubsurfaceColor 重定义逻辑 |
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| `Shaders/Private/DeferredShadingCommon.ush` | GBufferD 写入 |
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