UE4 顶点着色 学习笔记

void UVertexPainterBPLibrary::PaintVertexColorByIndex(UStaticMeshComponent* StaticMeshComponent, FColor LinearColor, int Index, int LODIndex)
{ 
	if (!StaticMeshComponent || !StaticMeshComponent->GetStaticMesh()) {
		return;
	}
	const int LODNum = StaticMeshComponent->GetStaticMesh()->GetNumLODs();
	StaticMeshComponent->SetLODDataCount(LODNum, LODNum);
	if (!StaticMeshComponent->LODData.IsValidIndex(LODIndex)) {
		return;
	}
	FStaticMeshComponentLODInfo& LODInfo = StaticMeshComponent->LODData[LODIndex];

	const int32 VertexNum = StaticMeshComponent->GetStaticMesh()->GetRenderData()->LODResources[LODIndex].GetNumVertices();

	if (Index < 0 || Index >= VertexNum) {
		return;
	}

	TArray VertexColors;
	LODInfo.OverrideVertexColors->GetVertexColors(VertexColors);
	VertexColors[Index] = LinearColor;
	LODInfo.OverrideVertexColors = new FColorVertexBuffer;
	LODInfo.OverrideVertexColors->InitFromColorArray(VertexColors);

	BeginInitResource(LODInfo.OverrideVertexColors);
}

首先区别一下StaticMesh和StaticMeshComponent

StaticMesh是模型本身

而StaticMeshComponent是模型出来的实例

直接修改StaticMesh的内容，所有StaticMeshComponent实例都会产生变化

而修改StaticMeshComponent直会对实例产生影响不会对StaticMesh有任何修改

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函数参数

1、要修改顶点着色的StaticMeshCommponent

2、第二个顶点所修改成的颜色

3、顶点的下标，具体修改的是哪一个顶点

4、LOD的下标，根据距离不同启用不同的LOD，对应顶点数量也会发生变化。

总结：

具体哪一个模型的哪一个LOD下的哪一个顶点，修改成什么颜色

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if (!StaticMeshComponent || !StaticMeshComponent->GetStaticMesh()) {
        return;
}

如果StaticMeshComponent为空，或者StaticMeshComponent对应的StaticMesh为空，则退出函数执行

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const int LODNum = StaticMeshComponent->GetStaticMesh()->GetNumLODs();
StaticMeshComponent->SetLODDataCount(LODNum, LODNum);

获取StaticMeshComponent所使用的StaticMesh的LOD数量，将之LOD数量设置为，StaticMeshComponent的LOD上

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if (!StaticMeshComponent->LODData.IsValidIndex(LODIndex)) {
        return;
}

如果函数参数的LODIndex是无效的，则不执行函数后续

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FStaticMeshComponentLODInfo& LODInfo = StaticMeshComponent->LODData[LODIndex];

const int32 VertexNum = StaticMeshComponent->GetStaticMesh()->GetRenderData()->LODResources[LODIndex].GetNumVertices();

获取StaticMeshComponent的LOD信息

USTRUCT()
struct FStaticMeshComponentLODInfo
{
	GENERATED_USTRUCT_BODY()

	/** Uniquely identifies this LOD's built map data. */
	FGuid MapBuildDataId;

	/** Used during deserialization to temporarily store legacy lightmap data. */
	FMeshMapBuildData* LegacyMapBuildData;

	/** 
	 * Transient override lightmap data, used by landscape grass.
	 * Be sure to add your component to UMapBuildDataRegistry::CleanupTransientOverrideMapBuildData() for proper cleanup
	 * so that you don't get stale rendering resource references if the underlying MapBuildData is gone (lighting scenario changes, new static lighting build, etc.)
	 */
	TUniquePtr OverrideMapBuildData;

	/** Vertex data cached at the time this LOD was painted, if any */
	TArray PaintedVertices;

	/** Vertex colors to use for this mesh LOD */
	FColorVertexBuffer* OverrideVertexColors;

	/** Information for each section about what range of PreCulledIndexBuffer to use.  If no preculled index data is available, PreCulledSections will be empty. */
	TArray PreCulledSections;

	FRawStaticIndexBuffer PreCulledIndexBuffer;

	/** 
	 * Owner of this FStaticMeshComponentLODInfo 
	 * Warning, can be NULL for a component created via SpawnActor off of a blueprint default (LODData will be created without a call to SetLODDataCount).
	 */
	class UStaticMeshComponent* OwningComponent;

	/** Default constructor */
	FStaticMeshComponentLODInfo();
	FStaticMeshComponentLODInfo(UStaticMeshComponent* InOwningComponent);
	/** Destructor */
	~FStaticMeshComponentLODInfo();

	/** Delete existing resources */
	void CleanUp();

	/** 
	 * Ensure this LODInfo has a valid MapBuildDataId GUID.
	 * @param LodIndex Index of the LOD this LODInfo represents.
	 * @return true if a new GUID was created, false otherwise.
	 */
	ENGINE_API bool CreateMapBuildDataId(int32 LodIndex);

	/**
	* Enqueues a rendering command to release the vertex colors.
	* The game thread must block until the rendering thread has processed the command before deleting OverrideVertexColors.
	*/
	ENGINE_API void BeginReleaseOverrideVertexColors();

	ENGINE_API void ReleaseOverrideVertexColorsAndBlock();

	void ReleaseResources();

	/** Methods for importing and exporting the painted vertex array to text */
	void ExportText(FString& ValueStr);
	void ImportText(const TCHAR** SourceText);

	/** Serializer. */
	friend FArchive& operator<<(FArchive& Ar,FStaticMeshComponentLODInfo& I);

private:
	/** Purposely hidden */
	FStaticMeshComponentLODInfo &operator=( const FStaticMeshComponentLODInfo &rhs ) { check(0); return *this; }
};

该结构体内有对应LOD的顶点颜色

然后获取对应的顶点个数

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if (Index < 0 || Index >= VertexNum) {
        return;
}
如果顶点个数不合法，则不执行后续逻辑

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TArray VertexColors;
LODInfo.OverrideVertexColors->GetVertexColors(VertexColors);
VertexColors[Index] = LinearColor;
LODInfo.OverrideVertexColors = new FColorVertexBuffer;
LODInfo.OverrideVertexColors->InitFromColorArray(VertexColors);

将顶点颜色赋值，然后刷新颜色

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BeginInitResource(LODInfo.OverrideVertexColors);

开始初始化资源

记得用这个函数加对应模块

"RenderCore"

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总结：就是把LODInfo.OverrideVertexColors重新刷新颜色

最后记住模型加上Vertex Color的材质

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void UVertexPainterBPLibrary::PaintVertexColorByIndex(UStaticMeshComponent* StaticMeshComponent, FColor LinearColor, int Index, int LODIndex)
{ 
	if (!StaticMeshComponent || !StaticMeshComponent->GetStaticMesh()) {
		return;
	}
	const int LODNum = StaticMeshComponent->GetStaticMesh()->GetNumLODs();
	StaticMeshComponent->SetLODDataCount(LODNum, LODNum);
	if (!StaticMeshComponent->LODData.IsValidIndex(LODIndex)) {
		return;
	}
	FStaticMeshComponentLODInfo& LODInfo = StaticMeshComponent->LODData[LODIndex];

	FStaticMeshLODResourcesArray& LODResourcesArray = StaticMeshComponent->GetStaticMesh()->GetRenderData()->LODResources;
	const int32 VertexNum = LODResourcesArray[LODIndex].GetNumVertices();

	if (Index < 0 || Index >= VertexNum) {
		return;
	}

	TArray VertexColors;

	if (LODInfo.OverrideVertexColors) {
		LODInfo.OverrideVertexColors->GetVertexColors(VertexColors);
	}
	else {
		if (LODResourcesArray[LODIndex].bHasColorVertexData) {
			LODResourcesArray[LODIndex].VertexBuffers.ColorVertexBuffer.GetVertexColors(VertexColors);
		}
		else {
			VertexColors.Init(FColor::White, VertexNum);
		}
	}
	VertexColors.SetNum(VertexNum);
	
	VertexColors[Index] = LinearColor;
	LODInfo.OverrideVertexColors = new FColorVertexBuffer;
	LODInfo.OverrideVertexColors->InitFromColorArray(VertexColors);

	BeginInitResource(LODInfo.OverrideVertexColors);
}

增加了一部分初始化LODInfo.OverrideVertexColors信息

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TArray UVertexPainterBPLibrary::GetVertexColorsInLOD(UStaticMeshComponent* StaticMeshComponent, int32 LODIndex) {
	TArray VertexColors;
	if (!StaticMeshComponent || !StaticMeshComponent->GetStaticMesh()) {
		return VertexColors;
	}
	const int LODNum = StaticMeshComponent->GetStaticMesh()->GetNumLODs();
	if (LODIndex < 0 || LODIndex >= LODNum) {
		return VertexColors;
	}
	FStaticMeshComponentLODInfo& LODInfo = StaticMeshComponent->LODData[LODIndex];
	FStaticMeshLODResourcesArray& LODResourcesArray = StaticMeshComponent->GetStaticMesh()->GetRenderData()->LODResources;
	const int32 VertexNum = LODResourcesArray[LODIndex].GetNumVertices();
	if (StaticMeshComponent->LODData.IsValidIndex(LODIndex)) {
		if (LODInfo.OverrideVertexColors) {
			LODInfo.OverrideVertexColors->GetVertexColors(VertexColors);
			VertexColors.SetNum(VertexNum);
			return VertexColors;
		}
	}
	{
		if (LODResourcesArray[LODIndex].bHasColorVertexData) {
			LODResourcesArray[LODIndex].VertexBuffers.ColorVertexBuffer.GetVertexColors(VertexColors);
		}
		else {
			VertexColors.Init(FColor::White, VertexNum);
		}
	}
	VertexColors.SetNum(VertexNum);
	return VertexColors;
}

void UVertexPainterBPLibrary::PaintVertexColorOnSphere(UStaticMeshComponent* StaticMeshComponent, FColor LinearColor, float Radius, FVector Position)
{
	if (!StaticMeshComponent || !StaticMeshComponent->GetStaticMesh()) {
		return;
	}
	const int LODNum = StaticMeshComponent->GetStaticMesh()->GetNumLODs();
	StaticMeshComponent->SetLODDataCount(LODNum, LODNum);

	const FTransform& LocalToWorld = StaticMeshComponent->GetComponentTransform();
	int LODIndex = 0;
	for (FStaticMeshComponentLODInfo& LODInfo : StaticMeshComponent->LODData) {
		const FPositionVertexBuffer& PositionVertexBuffer = StaticMeshComponent->GetStaticMesh()->GetRenderData()->
			LODResources[LODIndex].VertexBuffers.PositionVertexBuffer;
		int VertexNum = PositionVertexBuffer.GetNumVertices();
		TArray VertexColors = GetVertexColorsInLOD(StaticMeshComponent, LODIndex++);
		for (int i = 0; i < VertexNum; i++) {
			FVector VertexPosition = UKismetMathLibrary::TransformLocation(LocalToWorld, FVector(PositionVertexBuffer.VertexPosition(i)));
			float NormalizedDistance = UKismetMathLibrary::Vector_Distance(VertexPosition, Position)/Radius;
			if (NormalizedDistance <= 1) {
				VertexColors[i] = LinearColor;
			}
		}
		LODInfo.OverrideVertexColors = new FColorVertexBuffer;
		LODInfo.OverrideVertexColors->InitFromColorArray(VertexColors);

		BeginInitResource(LODInfo.OverrideVertexColors);
	}
	StaticMeshComponent->MarkRenderStateDirty();
	StaticMeshComponent->bDisallowMeshPaintPerInstance = true;
}

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    TArray VertexColors;
    if (!StaticMeshComponent || !StaticMeshComponent->GetStaticMesh()) {
        return VertexColors;
    }
    const int LODNum = StaticMeshComponent->GetStaticMesh()->GetNumLODs();
    if (LODIndex < 0 || LODIndex >= LODNum) {
        return VertexColors;
    }

前面依然是一个判断违规使用函数的条件

FStaticMeshComponentLODInfo& LODInfo = StaticMeshComponent->LODData[LODIndex];
    FStaticMeshLODResourcesArray& LODResourcesArray = StaticMeshComponent->GetStaticMesh()->GetRenderData()->LODResources;
    const int32 VertexNum = LODResourcesArray[LODIndex].GetNumVertices();
这里拿到LOD信息，然后获取LOD资源的数组，最后拿到顶点的数量

if (StaticMeshComponent->LODData.IsValidIndex(LODIndex)) {
        if (LODInfo.OverrideVertexColors) {
            LODInfo.OverrideVertexColors->GetVertexColors(VertexColors);
            VertexColors.SetNum(VertexNum);
            return VertexColors;
        }
    }
    {
        if (LODResourcesArray[LODIndex].bHasColorVertexData) {
            LODResourcesArray[LODIndex].VertexBuffers.ColorVertexBuffer.GetVertexColors(VertexColors);
        }
        else {
            VertexColors.Init(FColor::White, VertexNum);
        }
    }

这里初始化顶点颜色信息，防止获取到空颜色，造成报错

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VertexColors.SetNum(VertexNum);
return VertexColors;

最后设置顶点颜色数组的长度，防止多取少取

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if (!StaticMeshComponent || !StaticMeshComponent->GetStaticMesh()) {
        return;
}

防止错误的输入

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const int LODNum = StaticMeshComponent->GetStaticMesh()->GetNumLODs();
StaticMeshComponent->SetLODDataCount(LODNum, LODNum);

从StaticMesh的LOD数量设置到StaticMeshComponent里面去

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const FTransform& LocalToWorld = StaticMeshComponent->GetComponentTransform();
int LODIndex = 0;

这里拿到Component在场景的世界变换信息

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for (FStaticMeshComponentLODInfo& LODInfo : StaticMeshComponent->LODData) {
        const FPositionVertexBuffer& PositionVertexBuffer = StaticMeshComponent->GetStaticMesh()->GetRenderData()->
        LODResources[LODIndex].VertexBuffers.PositionVertexBuffer;
        int VertexNum = PositionVertexBuffer.GetNumVertices();
        TArray VertexColors = GetVertexColorsInLOD(StaticMeshComponent, LODIndex++);
        for (int i = 0; i < VertexNum; i++) {
        FVector VertexPosition = UKismetMathLibrary::TransformLocation(LocalToWorld, FVector(PositionVertexBuffer.VertexPosition(i)));
        float NormalizedDistance = UKismetMathLibrary::Vector_Distance(VertexPosition, Position)/Radius;
        if (NormalizedDistance <= 1) {
                VertexColors[i] = LinearColor;
            }
        }
        LODInfo.OverrideVertexColors = new FColorVertexBuffer;
        LODInfo.OverrideVertexColors->InitFromColorArray(VertexColors);

        BeginInitResource(LODInfo.OverrideVertexColors);
    }

先开始拿到顶点缓冲位置，这个信息是在LODResources里面，LOD里面有Vertex信息，当然顶点的位置信息也包括在里面

FPositionVertexBuffer是继承自VertexBuffer的

顶点数量，顶点位置的信息都在FVertexBuffer里面

接下来TArray获取到顶点颜色的所有颜色，通过第一个函数获取，就不赘述

接下来就是对每个顶点进行赋值颜色信息，通过TransformLocation函数，可以将本地的VertexPosition转化为世界场景坐标

 float NormalizedDistance = UKismetMathLibrary::Vector_Distance(VertexPosition, Position)/Radius;

if (NormalizedDistance <= 1) {
                VertexColors[i] = LinearColor;
}

若顶点距离和着色距离范围内，则进行着色

最后这里都讲过

LODInfo.OverrideVertexColors = new FColorVertexBuffer;
LODInfo.OverrideVertexColors->InitFromColorArray(VertexColors);

BeginInitResource(LODInfo.OverrideVertexColors);

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StaticMeshComponent->MarkRenderStateDirty();
StaticMeshComponent->bDisallowMeshPaintPerInstance = true;

防止第二个实例顶点着色无效

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TArray UVertexPainterBPLibrary::GetSkeletalVertexColorsInLOD(USkeletalMeshComponent* SkeletalMeshComponent, int32 LODIndex) {
	TArray VertexColors;
	if (!SkeletalMeshComponent || !SkeletalMeshComponent->SkeletalMesh) {
		return VertexColors;
	}
	const int LODNum = SkeletalMeshComponent->SkeletalMesh->GetLODNum();
	if (LODIndex < 0 || LODIndex >= LODNum) {
		return VertexColors;
	}
	FSkelMeshComponentLODInfo& LODInfo = SkeletalMeshComponent->LODInfo[LODIndex];
	FSkeletalMeshLODRenderData& LODResourcesArray = SkeletalMeshComponent->SkeletalMesh->GetResourceForRendering()->LODRenderData[LODIndex];
	const int32 VertexNum = LODResourcesArray.GetNumVertices();
	if (SkeletalMeshComponent->LODInfo.IsValidIndex(LODIndex)) {
		if (LODInfo.OverrideVertexColors) {
			LODInfo.OverrideVertexColors->GetVertexColors(VertexColors);
			VertexColors.SetNum(VertexNum);
			return VertexColors;
		}
	}
	{
		VertexColors.Init(FColor::White, VertexNum);
	}
	VertexColors.SetNum(VertexNum);
	return VertexColors;
}

void UVertexPainterBPLibrary::PaintVertexColorOnSkeletal(USkeletalMeshComponent* SkeletalMeshComponent, FColor LinearColor, float Radius, FVector Position) {
	if (!SkeletalMeshComponent || !SkeletalMeshComponent->SkeletalMesh) {
		return;
	}
	SkeletalMeshComponent->InitLODInfos();

	const FTransform& LocalToWorld = SkeletalMeshComponent->GetComponentTransform();
	int LODIndex = 0;
	for (FSkelMeshComponentLODInfo& LODInfo : SkeletalMeshComponent->LODInfo) {
		FSkeletalMeshLODRenderData& LODRenderData = SkeletalMeshComponent->SkeletalMesh->GetResourceForRendering()->LODRenderData[LODIndex];
		const int VertexNum = LODRenderData.GetNumVertices();
		FSkinWeightVertexBuffer& SkinWeightVertexBuffer = LODRenderData.SkinWeightVertexBuffer;
		TArray VertexColors = GetSkeletalVertexColorsInLOD(SkeletalMeshComponent, LODIndex++);
		for (int i = 0; i < VertexNum; i++) {
			FVector VertexPosition = UKismetMathLibrary::TransformLocation(LocalToWorld, FVector(USkeletalMeshComponent::GetSkinnedVertexPosition(SkeletalMeshComponent, i,
				LODRenderData, SkinWeightVertexBuffer))); 
			float NormalizedDistance = UKismetMathLibrary::Vector_Distance(VertexPosition, Position) / Radius;
			if (NormalizedDistance <= 1) {
				VertexColors[i] = LinearColor;
			}
		}
		LODInfo.OverrideVertexColors = new FColorVertexBuffer;
		LODInfo.OverrideVertexColors->InitFromColorArray(VertexColors);

		BeginInitResource(LODInfo.OverrideVertexColors);
	}
	SkeletalMeshComponent->MarkRenderStateDirty();
}

最后来一个支持谷歌模型的顶点绘制

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