385 lines
21 KiB
Markdown
385 lines
21 KiB
Markdown
---
|
||
title: VirtualTexture学习笔记
|
||
date: 2024-02-20 18:26:49
|
||
excerpt:
|
||
tags:
|
||
rating: ⭐
|
||
---
|
||
# 前言
|
||
- UE4 Runtime Virtual Texture 实现机制及源码解析:https://zhuanlan.zhihu.com/p/143709152
|
||
- UE Virtual Texture图文浅析:https://zhuanlan.zhihu.com/p/642580472
|
||
|
||
## 相关概念
|
||
- Virtual Texture：虚拟纹理，以下简称 VT
|
||
- Runtime Virtual Texture：UE4 运行时虚拟纹理系统，以下简称 RVT
|
||
- VT feedback：存储当前屏幕像素对应的 VT Page 信息，用于加载 VT 数据。
|
||
- VT Physical Texture：虚拟纹理对应的物理纹理资源
|
||
- PageTable：虚拟纹理页表，用来寻址 VT Physical Texture Page 数据。
|
||
- PageTable Texture：包含虚拟纹理页表数据的纹理资源，通过此纹理资源可查询 Physical Texture Page 信息。有些 VT 系统也叫 Indirection Texture，由于本文分析 UE4 VT 的内容，这里采用 UE4 术语。
|
||
- PageTable Buffer：包含虚拟纹理页表数据内容的 GPU Buffer 资源。
|
||
|
||
相关类：
|
||
- URuntimeVirtualTexture（UObject）
|
||
- FRuntimeVirtualTextureRenderResource
|
||
- UVirtualTexture（UObject）
|
||
- UVirtualTexture2D（UTexture2D）
|
||
|
||
# UE5 VirtualHeightfieldMesh简述
|
||
https://zhuanlan.zhihu.com/p/575398476
|
||
|
||
## 可能的相关类
|
||
- VirtualHeightfieldMesh
|
||
- UVirtualHeightfieldMeshComponent
|
||
- **UHeightfieldMinMaxTexture**
|
||
- BuildTexture()
|
||
- FVirtualHeightfieldMeshSceneProxy
|
||
- FVirtualHeightfieldMeshRendererExtension
|
||
- AddWork()
|
||
- **SubmitWork()**
|
||
- FVirtualTextureFeedbackBuffer 参考[[#Pass1的补充VirtualTextureFeedback]]
|
||
- UNiagaraDataInterfaceLandscape
|
||
- UNiagaraDataInterfaceVirtualTexture(**NiagaraDataInterfaceVirtualTextureTemplate.ush**)
|
||
- GetAttributesValid()
|
||
- SampleRVTLayer()
|
||
- SampleRVT()
|
||
- URuntimeVirtualTextureComponent
|
||
|
||
## VirtualHeightfieldMesh
|
||
首先是MinMaxTexture。全称**UHeightfieldMinMaxTexture**（下简称MinMaxTexture），可以说是整个VHM中最重要的部分之一。它是离线生成的，目的主要是以下几个：
|
||
1. 用作Instance的剔除（遮挡剔除查询＋Frustum剔除）
|
||
2. 用作决定VHM的LOD
|
||
3. 用作平滑VHM的顶点位置
|
||
|
||
其中比较关键的几个成员变量为：
|
||
- TObjectPtr<class UTexture2D> Texture：BGRA8格式、贴图大小与RVT的Tile数量一致、有全部mipmap。每个像素存储RVT一个Tile中的最小值以及最大值，各为16bit、encode在RGBA的4个通道上。
|
||
- TObjectPtr<class UTexture2D> LodBiasTexture：G8格式、贴图大小与RTV的Tile数量一致、无mipmap。每个像素存储了Texture对应像素周围3x3blur之后的结果。
|
||
- TObjectPtr<class UTexture2D> LodBiasMinMaxTexture：BGRA8格式、贴图大小与RTV的Tile数量一致、有全部mipmap。类似于HZB、每个像素存储LodBiasTexture的最小值以及最大值，各为8bit、存在RG两个通道上。
|
||
- int32 MaxCPULevels：表示共需要在CPU端存储多少层level的数据。
|
||
- TArray`<FVector2D>` TextureData：CPU端存储Texture贴图的数据，共MaxCPULevels层mipmap。
|
||
|
||
### TextureData的获取
|
||
因此要生成MinMaxTexture、最关键的就是要得到TextureData，其入口函数为位于**HeightfieldMinMaxTextureBuilder.cpp**的**VirtualHeightfieldmesh::BuildMinMaxTexture**中。由于Texture存储的是RVT中每个Tile中最小最大值，因此不难想象到其大致流程可以分为以下几步：
|
||
1. 遍历RVT的每个Tile并绘制到一张中间贴图上，然后计算这张中间纹理的最小最大值、存储至目标贴图对应的位置上；
|
||
2. 为目标贴图生成mipmap；
|
||
3. 将目标贴图回读至CPU、得到TextureData。
|
||
|
||
将Tile绘制到一张中间贴图使用的是自带的***RuntimeVirtualTexture::RenderPagesStandAlone***函数；计算最小最大值是通过Downsample的方式计算而成。如下图所示为2x2Tiles、4TileSize的RVT，计算Tile0的最小最大值的示意过程图：
|
||
|
||
|
||
Downsample的ComputeShader为**TMinMaxTextureCS**。遍历计算完每个Tile的最小最大值后，同样通过Downsample为目标贴图生成全mipmap。
|
||
|
||
最后为了将贴图回读到CPU，先是通过CopyTexture的方式将目标贴图的各个mipmap复制到各自带有CPUReadback Flag的贴图后，再通过MapStagingSurface/UnmapStagingSurface的方式复制到CPU内存上。由于是比较常规的操作，就不过多介绍了。
|
||
|
||
至此也就得到了带有所有mipmap的CPU端的TextureData，接着将此作为参数调用UHeightfieldMinMaxTexture::BuildTexture以生成剩下的内容（即Texture、LodBiasTexture、LodBiasMinMaxTexture）。
|
||
|
||
### FVirtualHeightfieldMeshSceneProxy
|
||
至此离线生成的MinMaxTexture介绍完毕，后面都是实时渲染内容的介绍部分。所有内容都围绕着VHM的SceneProxy也就是**FVirtualHeightfieldMeshSceneProxy**展开。
|
||
|
||
#### 遮挡剔除
|
||
> 关于硬件的遮挡剔除用法可以参考DX12的官方sample[[8]](https://zhuanlan.zhihu.com/p/575398476#ref_8)
|
||
|
||
首先是遮挡剔除部分，VHM做了Tile级别且带有LOD的遮挡剔除。VHM的SceneProxy重写了函数GetOcclusionQueries，函数实现只是简单地返回OcclusionVolumes：
|
||
|
||
OcclusionVolumes的构建在函数BuildOcclusionVolumes中，其基本思路为取MinMaxTexture中**CPU端的TextureData**的数据、获得每个Tile的高度最小最大值来创建该Tile的Bounds信息。
|
||
|
||
可以看到OcclusionVolumes是带有Lod的。当然实际上这里的代码的LodIndex不一定从0开始，因为Component中有一项成员变量**NumOcclusionLod**、表示创建多少层mipmap的OcclusionVolumes。另外有一点需要注意的是，NumOcclusionLod默认值为0、也就是说VHM的遮挡剔除默认没有开启。
|
||
|
||
|
||
由于VHM需要在ComputePass中动态地构建Instance绘制的IndirectArgs、因此SceneProxy还重写了函数AcceptOcclusionResults，用以获取遮挡剔除的结果。具体是将UE返回的遮挡剔除的结果存在贴图OcclusionTexture上、以便能够作为SRV在后续的Pass中访问：
|
||
```cpp
|
||
void FVirtualHeightfieldMeshSceneProxy::AcceptOcclusionResults(FSceneView const* View, TArray<bool>* Results, int32 ResultsStart, int32 NumResults)
|
||
{
|
||
// 由于构建IndirectArgs跟SceneProxy不在同一个地方，因此用了一个全局变量来保存遮挡剔除的结果
|
||
FOcclusionResults& OcclusionResults = GOcclusionResults.Emplace(FOcclusionResultsKey(this, View));
|
||
OcclusionResults.TextureSize = OcclusionGridSize;
|
||
OcclusionResults.NumTextureMips = NumOcclusionLods;
|
||
|
||
// 创建贴图，并将遮挡剔除结果Copy至贴图上
|
||
FRHIResourceCreateInfo CreateInfo(TEXT("VirtualHeightfieldMesh.OcclusionTexture"));
|
||
OcclusionResults.OcclusionTexture = RHICreateTexture2D(OcclusionGridSize.X, OcclusionGridSize.Y, PF_G8, NumOcclusionLods, 1, TexCreate_ShaderResource, CreateInfo);
|
||
bool const* Src = Results->GetData() + ResultsStart;
|
||
FIntPoint Size = OcclusionGridSize;
|
||
for (int32 MipIndex = 0; MipIndex < NumOcclusionLods; ++MipIndex)
|
||
{
|
||
uint32 Stride;
|
||
uint8* Dst = (uint8*)RHILockTexture2D(OcclusionResults.OcclusionTexture, MipIndex, RLM_WriteOnly, Stride, false);
|
||
for (int Y = 0; Y < Size.Y; ++Y)
|
||
{
|
||
for (int X = 0; X < Size.X; ++X)
|
||
{
|
||
Dst[Y * Stride + X] = *(Src++) ? 255 : 0;
|
||
}
|
||
}
|
||
RHIUnlockTexture2D(OcclusionResults.OcclusionTexture, MipIndex, false);
|
||
|
||
Size.X = FMath::Max(Size.X / 2, 1);
|
||
Size.Y = FMath::Max(Size.Y / 2, 1);
|
||
}
|
||
}
|
||
```
|
||
|
||
### 整体思路
|
||
至此就开始真正的VHM的Mesh的数据构建了。为了后续的代码细节能够更加易懂，这里再说明一下VHM构建mesh的整体思路：假设我们有一个工作队列为QueueBuffer，每一项工作就是从QueueBuffer中取出一项工作（更准确地说，取出一个Quad）、对这个Quad判断是否需要进行细化、如果需要细分则将这个Quad细分为4个Quad并塞入QueueBuffer中。
|
||
|
||
重复这个取出→处理→放回的过程，直到QueueBuffer中没有工作为止。示意图如下：
|
||
|
||
|
||
|
||
### RVT相关代码（Pass1：CollectQuad）
|
||
如果不能细分，那么就会增加一个Instance、将其Instance的数据写入RWQuadBuffer中。RWQuadBuffer将会用在后续的CullInstance Pass中，以真正地构建IndirectArgs：
|
||
```c++
|
||
// 无法继续细分的情况
|
||
// 用以后续对RVT进行采样
|
||
uint PhysicalAddress = PageTableTexture.Load(int3(Pos, Level));
|
||
|
||
InterlockAdd(RWQuadInfo.Write, 1, Write);
|
||
RWQuadBuffer[Write] = Pack(InitQuadRenderItem(Pos, Level, PhysicalAddress, bCull | bOcclude));
|
||
```
|
||
|
||
> 其中的RWQuadInfo是我编的变量名、实际的代码中并不存在。或者说实际上这里的变量名是RWIndirectArgsBuffer，但是并不是前面所说的用以绘制的IndirectArgs。为了不让大家混淆，这里改了下变量名
|
||
> 另外也能由此看出的是，VHM也许曾经想过利用IndirectArgs数组来绘制（即DXSample中将符合条件的生成IndirectArgs放进数组中）。但是最后改成的是一个IndirectArgs但是Instance的绘制方式
|
||
|
||
PS. PageTableTexture的类型为**RHITextuire**。相关Shader代码位于**VirtualHeightfieldMesh.usf**
|
||
|
||
#### Pass1的补充VirtualTextureFeedback
|
||
不再继续进行细分后、说明后续就要对该Level的RVT进行采样，因此需要处理对应的Feedback信息、让虚幻可以加载对应的Page。shader代码如下图所示：
|
||
|
||
|
||
c++中则要将这个RWFeedbackBuffer喂给虚幻的函数**SubmitVirtualTextureFeedbackBuffer**：
|
||
|
||
|
||
### 相关代码段
|
||
```c++
|
||
FVertexFactoryIntermediates GetVertexFactoryIntermediates(FVertexFactoryInput Input)
|
||
{
|
||
...
|
||
|
||
// Sample height from virtual texture.
|
||
VTUniform Uniform = VTUniform_Unpack(VHM.VTPackedUniform);
|
||
Uniform.vPageBorderSize -= .5f * VHM.PhysicalTextureSize.y; // Half texel offset is used in VT write and in sampling because we want texel locations to match landscape vertices.
|
||
VTPageTableUniform PageTableUniform = VTPageTableUniform_Unpack(VHM.VTPackedPageTableUniform0, VHM.VTPackedPageTableUniform1);
|
||
VTPageTableResult VTResult0 = TextureLoadVirtualPageTableLevel(VHM.PageTableTexture, PageTableUniform, NormalizedPos, VTADDRESSMODE_CLAMP, VTADDRESSMODE_CLAMP, floor(SampleLevel));
|
||
float2 UV0 = VTComputePhysicalUVs(VTResult0, 0, Uniform);
|
||
float Height0 = VHM.HeightTexture.SampleLevel(VHM.HeightSampler, UV0, 0);
|
||
VTPageTableResult VTResult1 = TextureLoadVirtualPageTableLevel(VHM.PageTableTexture, PageTableUniform, NormalizedPos, VTADDRESSMODE_CLAMP, VTADDRESSMODE_CLAMP, ceil(SampleLevel));
|
||
float2 UV1 = VTComputePhysicalUVs(VTResult1, 0, Uniform);
|
||
float Height1 = VHM.HeightTexture.SampleLevel(VHM.HeightSampler, UV1, 0);
|
||
float Height = lerp(Height0.x, Height1.x, frac(SampleLevel));
|
||
|
||
...
|
||
}
|
||
```
|
||
|
||
渲染线程创建VT的相关逻辑：
|
||
```c++
|
||
void FVirtualHeightfieldMeshSceneProxy::CreateRenderThreadResources()
|
||
{
|
||
if (RuntimeVirtualTexture != nullptr)
|
||
{
|
||
if (!bCallbackRegistered)
|
||
{
|
||
GetRendererModule().AddVirtualTextureProducerDestroyedCallback(RuntimeVirtualTexture->GetProducerHandle(), &OnVirtualTextureDestroyedCB, this);
|
||
bCallbackRegistered = true;
|
||
}
|
||
|
||
//URuntimeVirtualTexture* RuntimeVirtualTexture;
|
||
if (RuntimeVirtualTexture->GetMaterialType() == ERuntimeVirtualTextureMaterialType::WorldHeight)
|
||
{
|
||
AllocatedVirtualTexture = RuntimeVirtualTexture->GetAllocatedVirtualTexture();
|
||
NumQuadsPerTileSide = RuntimeVirtualTexture->GetTileSize();
|
||
|
||
if (AllocatedVirtualTexture != nullptr)
|
||
{
|
||
// Gather vertex factory uniform parameters.
|
||
FVirtualHeightfieldMeshVertexFactoryParameters UniformParams;
|
||
UniformParams.PageTableTexture = AllocatedVirtualTexture->GetPageTableTexture(0);
|
||
UniformParams.HeightTexture = AllocatedVirtualTexture->GetPhysicalTextureSRV(0, false);
|
||
UniformParams.HeightSampler = TStaticSamplerState<SF_Bilinear>::GetRHI();
|
||
UniformParams.LodBiasTexture = LodBiasTexture ? LodBiasTexture->GetResource()->TextureRHI : GBlackTexture->TextureRHI;
|
||
UniformParams.LodBiasSampler = TStaticSamplerState<SF_Point>::GetRHI();
|
||
UniformParams.NumQuadsPerTileSide = NumQuadsPerTileSide;
|
||
|
||
FUintVector4 PackedUniform;
|
||
AllocatedVirtualTexture->GetPackedUniform(&PackedUniform, 0);
|
||
UniformParams.VTPackedUniform = PackedUniform;
|
||
FUintVector4 PackedPageTableUniform[2];
|
||
AllocatedVirtualTexture->GetPackedPageTableUniform(PackedPageTableUniform);
|
||
UniformParams.VTPackedPageTableUniform0 = PackedPageTableUniform[0];
|
||
UniformParams.VTPackedPageTableUniform1 = PackedPageTableUniform[1];
|
||
|
||
const float PageTableSizeX = AllocatedVirtualTexture->GetWidthInTiles();
|
||
const float PageTableSizeY = AllocatedVirtualTexture->GetHeightInTiles();
|
||
UniformParams.PageTableSize = FVector4f(PageTableSizeX, PageTableSizeY, 1.f / PageTableSizeX, 1.f / PageTableSizeY);
|
||
|
||
const float PhysicalTextureSize = AllocatedVirtualTexture->GetPhysicalTextureSize(0);
|
||
UniformParams.PhysicalTextureSize = FVector2f(PhysicalTextureSize, 1.f / PhysicalTextureSize);
|
||
|
||
UniformParams.VirtualHeightfieldToLocal = FMatrix44f(UVToLocal);
|
||
UniformParams.VirtualHeightfieldToWorld = FMatrix44f(UVToWorld); // LWC_TODO: Precision loss
|
||
|
||
UniformParams.MaxLod = AllocatedVirtualTexture->GetMaxLevel();
|
||
UniformParams.LodBiasScale = LodBiasScale;
|
||
|
||
// Create vertex factory.
|
||
VertexFactory = new FVirtualHeightfieldMeshVertexFactory(GetScene().GetFeatureLevel(), UniformParams);
|
||
VertexFactory->InitResource(FRHICommandListImmediate::Get());
|
||
}
|
||
}
|
||
}
|
||
}
|
||
```
|
||
|
||
# RVT生成相关
|
||
|
||
# RVT相关操作总结
|
||
CPU端创建：
|
||
```c++
|
||
|
||
```
|
||
|
||
作为UniformParameter传递到GPU端：
|
||
```c++
|
||
AllocatedVirtualTexture = RuntimeVirtualTexture->GetAllocatedVirtualTexture();
|
||
|
||
//PageTableTexture、Texture&Sampler
|
||
FVirtualHeightfieldMeshVertexFactoryParameters UniformParams;
|
||
UniformParams.PageTableTexture = AllocatedVirtualTexture->GetPageTableTexture(0);
|
||
UniformParams.HeightTexture = AllocatedVirtualTexture->GetPhysicalTextureSRV(0, false);
|
||
UniformParams.HeightSampler = TStaticSamplerState<SF_Bilinear>::GetRHI();
|
||
|
||
//VTPackedUniform&VTPackedPageTableUniform
|
||
FUintVector4 PackedUniform;
|
||
AllocatedVirtualTexture->GetPackedUniform(&PackedUniform, 0);
|
||
UniformParams.VTPackedUniform = PackedUniform;
|
||
FUintVector4 PackedPageTableUniform[2];
|
||
AllocatedVirtualTexture->GetPackedPageTableUniform(PackedPageTableUniform);
|
||
UniformParams.VTPackedPageTableUniform0 = PackedPageTableUniform[0];
|
||
UniformParams.VTPackedPageTableUniform1 = PackedPageTableUniform[1];
|
||
|
||
//PageTableSize
|
||
const float PageTableSizeX = AllocatedVirtualTexture->GetWidthInTiles();
|
||
const float PageTableSizeY = AllocatedVirtualTexture->GetHeightInTiles();
|
||
UniformParams.PageTableSize = FVector4f(PageTableSizeX, PageTableSizeY, 1.f / PageTableSizeX, 1.f / PageTableSizeY);
|
||
|
||
//PhysicalTextureSize
|
||
const float PhysicalTextureSize = AllocatedVirtualTexture->GetPhysicalTextureSize(0);
|
||
UniformParams.PhysicalTextureSize = FVector2f(PhysicalTextureSize, 1.f / PhysicalTextureSize);
|
||
|
||
//Local <=> World Matrix
|
||
UniformParams.VirtualHeightfieldToLocal = FMatrix44f(UVToLocal);
|
||
UniformParams.VirtualHeightfieldToWorld = FMatrix44f(UVToWorld); // LWC_TODO: Precision loss
|
||
|
||
//MaxLod
|
||
UniformParams.MaxLod = AllocatedVirtualTexture->GetMaxLevel();
|
||
```
|
||
|
||
GPU端采样：
|
||
```c++
|
||
VTUniform Uniform = VTUniform_Unpack(VHM.VTPackedUniform);
|
||
Uniform.vPageBorderSize -= .5f * VHM.PhysicalTextureSize.y; // Half texel offset is used in VT write and in sampling because we want texel locations to match landscape vertices.
|
||
VTPageTableUniform PageTableUniform = VTPageTableUniform_Unpack(VHM.VTPackedPageTableUniform0, VHM.VTPackedPageTableUniform1);
|
||
VTPageTableResult VTResult0 = TextureLoadVirtualPageTableLevel(VHM.PageTableTexture, PageTableUniform, NormalizedPos, VTADDRESSMODE_CLAMP, VTADDRESSMODE_CLAMP, floor(SampleLevel));
|
||
float2 UV0 = VTComputePhysicalUVs(VTResult0, 0, Uniform);
|
||
float Height0 = VHM.HeightTexture.SampleLevel(VHM.HeightSampler, UV0, 0);
|
||
VTPageTableResult VTResult1 = TextureLoadVirtualPageTableLevel(VHM.PageTableTexture, PageTableUniform, NormalizedPos, VTADDRESSMODE_CLAMP, VTADDRESSMODE_CLAMP, ceil(SampleLevel));
|
||
float2 UV1 = VTComputePhysicalUVs(VTResult1, 0, Uniform);
|
||
float Height1 = VHM.HeightTexture.SampleLevel(VHM.HeightSampler, UV1, 0);
|
||
float Height = lerp(Height0.x, Height1.x, frac(SampleLevel));
|
||
```
|
||
|
||
**NiagaraDataInterfaceVirtualTextureTemplate.ush**中的代码：
|
||
```c++
|
||
//其他相关VT操作函数位于VirtualTextureCommon.ush
|
||
|
||
float4 SampleRVTLayer_{ParameterName}(float2 SampleUV, Texture2D InTexture, Texture2D<uint4> InPageTable, uint4 InTextureUniforms)
|
||
{
|
||
VTPageTableResult PageTable = TextureLoadVirtualPageTableLevel(InPageTable, VTPageTableUniform_Unpack({ParameterName}_PageTableUniforms[0], {ParameterName}_PageTableUniforms[1]), SampleUV, VTADDRESSMODE_CLAMP, VTADDRESSMODE_CLAMP, 0.0f);
|
||
return TextureVirtualSample(InTexture, {ParameterName}_SharedSampler, PageTable, 0, VTUniform_Unpack(InTextureUniforms));
|
||
}
|
||
|
||
void SampleRVT_{ParameterName}(in float3 WorldPosition, out bool bInsideVolume, out float3 BaseColor, out float Specular, out float Roughness, out float3 Normal, out float WorldHeight, out float Mask)
|
||
{
|
||
bInsideVolume = false;
|
||
BaseColor = float3(0.0f, 0.0f, 0.0f);
|
||
Specular = 0.5f;
|
||
Roughness = 0.5f;
|
||
Normal = float3(0.0f, 0.0f, 1.0f);
|
||
WorldHeight = 0.0f;
|
||
Mask = 1.0f;
|
||
|
||
// Get Sample Location
|
||
FLWCVector3 LWCWorldPosition = MakeLWCVector3({ParameterName}_SystemLWCTile, WorldPosition);
|
||
FLWCVector3 LWCUVOrigin = MakeLWCVector3({ParameterName}_SystemLWCTile, {ParameterName}_UVUniforms[0].xyz);
|
||
|
||
float2 SampleUV = VirtualTextureWorldToUV(LWCWorldPosition, LWCUVOrigin, {ParameterName}_UVUniforms[1].xyz, {ParameterName}_UVUniforms[2].xyz);
|
||
|
||
// Test to see if we are inside the volume, but still take the samples as it will clamp to the edge
|
||
bInsideVolume = all(SampleUV >- 0.0f) && all(SampleUV < 1.0f);
|
||
|
||
// Sample Textures
|
||
float4 LayerSample[3];
|
||
LayerSample[0] = ({ParameterName}_ValidLayersMask & 0x1) != 0 ? SampleRVTLayer_{ParameterName}(SampleUV, {ParameterName}_VirtualTexture0, {ParameterName}_VirtualTexture0PageTable, {ParameterName}_VirtualTexture0TextureUniforms) : 0;
|
||
LayerSample[1] = ({ParameterName}_ValidLayersMask & 0x2) != 0 ? SampleRVTLayer_{ParameterName}(SampleUV, {ParameterName}_VirtualTexture1, {ParameterName}_VirtualTexture1PageTable, {ParameterName}_VirtualTexture1TextureUniforms) : 0;
|
||
LayerSample[2] = ({ParameterName}_ValidLayersMask & 0x4) != 0 ? SampleRVTLayer_{ParameterName}(SampleUV, {ParameterName}_VirtualTexture2, {ParameterName}_VirtualTexture2PageTable, {ParameterName}_VirtualTexture2TextureUniforms) : 0;
|
||
|
||
// Sample Available Attributes
|
||
switch ( {ParameterName}_MaterialType )
|
||
{
|
||
case ERuntimeVirtualTextureMaterialType_BaseColor:
|
||
{
|
||
BaseColor = LayerSample[0].xyz;
|
||
break;
|
||
}
|
||
|
||
case ERuntimeVirtualTextureMaterialType_BaseColor_Normal_Roughness:
|
||
{
|
||
BaseColor = VirtualTextureUnpackBaseColorSRGB(LayerSample[0]);
|
||
Roughness = LayerSample[1].y;
|
||
Normal = VirtualTextureUnpackNormalBGR565(LayerSample[1]);
|
||
break;
|
||
}
|
||
|
||
case ERuntimeVirtualTextureMaterialType_BaseColor_Normal_DEPRECATED:
|
||
case ERuntimeVirtualTextureMaterialType_BaseColor_Normal_Specular:
|
||
{
|
||
BaseColor = LayerSample[0].xyz;
|
||
Specular = LayerSample[1].x;
|
||
Roughness = LayerSample[1].y;
|
||
Normal = VirtualTextureUnpackNormalBC3BC3(LayerSample[0], LayerSample[1]);
|
||
break;
|
||
}
|
||
|
||
case ERuntimeVirtualTextureMaterialType_BaseColor_Normal_Specular_YCoCg:
|
||
{
|
||
BaseColor = VirtualTextureUnpackBaseColorYCoCg(LayerSample[0]);
|
||
Specular = LayerSample[2].x;
|
||
Roughness = LayerSample[2].y;
|
||
Normal = VirtualTextureUnpackNormalBC5BC1(LayerSample[1], LayerSample[2]);
|
||
break;
|
||
}
|
||
|
||
case ERuntimeVirtualTextureMaterialType_BaseColor_Normal_Specular_Mask_YCoCg:
|
||
{
|
||
BaseColor = VirtualTextureUnpackBaseColorYCoCg(LayerSample[0]);
|
||
Specular = LayerSample[2].x;
|
||
Roughness = LayerSample[2].y;
|
||
Normal = VirtualTextureUnpackNormalBC5BC1(LayerSample[1], LayerSample[2]);
|
||
Mask = LayerSample[2].w;
|
||
break;
|
||
}
|
||
|
||
case ERuntimeVirtualTextureMaterialType_WorldHeight:
|
||
{
|
||
WorldHeight = VirtualTextureUnpackHeight(LayerSample[0], {ParameterName}_WorldHeightUnpack);
|
||
break;
|
||
}
|
||
}
|
||
}
|
||
```
|
||
|
||
VT还存在一个反馈机制，具体可以参考：[[#Pass1的补充VirtualTextureFeedback]]
|
||
```c++
|
||
/** GPU fence pool. Contains a fence array that is kept in sync with the FeedbackItems ring buffer. Fences are used to know when a transfer is ready to Map() without stalling. */
|
||
/** GPU 栅栏池。其中包含一个与 FeedbackItems 环形缓冲区保持同步的栅栏数组。栅栏用于了解传输何时准备就绪，可在不停滞的情况下进行 Map()。 */
|
||
class FFeedbackGPUFencePool* Fences;
|
||
``` |