UE4.27.2 纹理 Reimport With New File 的调试分析
2025-06-01 10:52:45 #Cpp #Unreal Engine 4 #Render

Reimport With New File 入口

FAssetFileContextMenu::ExecuteReimportWithNewFile 收集所有重新导入的资产，传给 FReimportManager::ValidateAllSourceFileAndReimport

FReimportManager::ValidateAllSourceFileAndReimport 处理那些丢失的资产对象 missing file，然后把剩下的那些资产对象传给 FReimportManager::ReimportMultiple

FReimportManager::ReimportMultiple 遍历资产对象，对每一个资产对象调用 FReimportManager::Reimport 进行重新导入

FReimportManager::Reimport 对这一个资产对象的所有源文件检查是否丢失等，然后寻找合适的 FReimportHandler，最终调用 FReimportHandler::Reimport 来重新导入

这是一个虚函数，以实现导入行为的多态

对于重新加载纹理，进入的是 UReimportTextureFactory::Reimport

最终到 UTextureFactory::FactoryCreateBinary，堆栈如下，就不分析了

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UTextureFactory::FactoryCreateBinary(UClass *, UObject *, FName, EObjectFlags, UObject *, const wchar_t *, const unsigned char *&, const unsigned char *, FFeedbackContext *) EditorFactories.cpp:4337
UFactory::FactoryCreateBinary(UClass *, UObject *, FName, EObjectFlags, UObject *, const wchar_t *, const unsigned char *&, const unsigned char *, FFeedbackContext *, bool &) Factory.h:354
UFactory::FactoryCreateFile(UClass *, UObject *, FName, EObjectFlags, const FString &, const wchar_t *, FFeedbackContext *, bool &) Factory.cpp:112
UFactory::ImportObject(UClass *, UObject *, FName, EObjectFlags, const FString &, const wchar_t *, bool &) Factory.cpp:201
UReimportTextureFactory::Reimport(UObject *) EditorFactories.cpp:6018
FReimportHandler::Reimport(UObject *, int) EditorReimportHandler.h:238
FReimportManager::Reimport(UObject *, bool, bool, FString, FReimportHandler *, int, bool, bool) Editor.cpp:375
FReimportManager::ReimportMultiple(TArrayView<…>, bool, bool, FString, FReimportHandler *, int, bool, bool) Editor.cpp:622
FReimportManager::ValidateAllSourceFileAndReimport(TArray<…> &, bool, int, bool, bool) Editor.cpp:583
FAssetFileContextMenu::ExecuteReimportWithNewFile(int) AssetFileContextMenu.cpp:1444

UTextureFactory::FactoryCreateBinary

删掉了类型检查、事件、UDIM、保存图片导入设置、guid、法线贴图、LOD 组、恢复图片导入设置、纹理数组、自动创建纹理等内容，精简为

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UObject* UTextureFactory::FactoryCreateBinary
(
	UClass*				Class,
	UObject*			InParent,
	FName				Name,
	EObjectFlags		Flags,
	UObject*			Context,
	const TCHAR*		Type,
	const uint8*&		Buffer,
	const uint8*			BufferEnd,
	FFeedbackContext*	Warn
)
{
	FName TextureName = Name;

	// if the texture already exists, remember the user settings
	UTexture* ExistingTexture = FindObject<UTexture>( InParent, *TextureName.ToString() );
	UTexture2D* ExistingTexture2D = FindObject<UTexture2D>( InParent, *TextureName.ToString() );

	if (ExistingTexture2D)
	{
		// Update with new settings, which should disable streaming...
		ExistingTexture2D->UpdateResource();
	}
	if(ExistingTexture)
	{
		// Wait for InitRHI() to complete before the FTextureReferenceReplacer calls ReleaseRHI() to follow the workflow.
		// Static texture needs to avoid having pending InitRHI() before enqueuing ReleaseRHI() to safely track access of the PlatformData on the renderthread.
		ExistingTexture->WaitForPendingInitOrStreaming();
	}
	
	FTextureReferenceReplacer RefReplacer(ExistingTexture);

	UTexture* Texture = nullptr;
	Texture = ImportTexture(Class, InParent, TextureName, Flags, Type, Buffer, BufferEnd, Warn);
    if (Texture)
    {
        Texture->AssetImportData->Update(CurrentFilename, FileHash.IsValid() ? &FileHash : nullptr);
    }

	if(!Texture)
	{
		if (ExistingTexture)
		{
			// We failed to import over the existing texture. Make sure the resource is ready in the existing texture.
			ExistingTexture->UpdateResource();
		}

		return nullptr;
	}

	//Replace the reference for the new texture with the existing one so that all current users still have valid references.
	RefReplacer.Replace(Texture);

	return Texture;
}

前面是确保被替换的纹理已经初始化了 RHI 资源

然后就是替换的核心逻辑了 RefReplacer.Replace(Texture);

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/** 
* Replaces the RHI reference of one texture with another.
* Allows one texture to be replaced with another at runtime and have all existing references to it remain valid.
*/
struct FTextureReferenceReplacer
{
	FTextureReferenceRHIRef OriginalRef;

	FTextureReferenceReplacer(UTexture* OriginalTexture)
	{
		if (OriginalTexture)
		{
			OriginalTexture->ReleaseResource();
			OriginalRef = OriginalTexture->TextureReference.TextureReferenceRHI;
		}
		else
		{
			OriginalRef = nullptr;
		}
	}

	void Replace(UTexture* NewTexture)
	{
		if (OriginalRef)
		{
			NewTexture->TextureReference.TextureReferenceRHI = OriginalRef;
		}
	}
};

搜索了整个引擎，只有 Editor 的这个 reimport 的功能使用了 FTextureReferenceReplacer 这个结构体

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2025-06-01 10:52:45 #Cpp #Unreal Engine 4 #Render
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