读取与导出本地图片

效果

  1. 通过代码读取本地的 png 图片（可自己扩展其它类型）转换为 UE4 内部可用的 Texture2D；

  2. 利用 UE4 内的 Texture2D 在本地指定目录下生成对应 png 图片；

  3. 利用 UE4 内的 Sprite 在本地指定目录下生成对应的 png 图片。

PNG -> Texture2D

分析

  1. 读取指定目录的 png 图片，将信息存入数组 RawFileData
  2. 用 ImageWrapper 来保存 RawFileData 转为可用信息
  3. 生成空的 Texture
  4. 将数据写入 Texture 中
  5. 保存资源

读取指定目录的 png 图片，将信息存入数组 RawFileData

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const FString PicturePath = ImageDirectory.Path + TEXT("/") + ImageName + TEXT(".png");

if (!FPlatformFileManager::Get().GetPlatformFile().FileExists(*PicturePath))
{
    // 不存在 PicturePath 文件
    return nullptr;
}

TArray<uint8> RawFileData;
if (!FFileHelper::LoadFileToArray(RawFileData, *PicturePath))
{
    // 无法解析 PicturePath
    return nullptr;
}

用 ImageWrapper 来保存 RawFileData 转为可用信息

需要依赖模块：ImageWrapper ，包含头文件：IImageWrapper.h、IImageWrapperModule.h

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IImageWrapperModule& ImageWrapperModule = FModuleManager::LoadModuleChecked<IImageWrapperModule>("ImageWrapper");

TSharedPtr<IImageWrapper> ImageWrapper = ImageWrapperModule.CreateImageWrapper(EImageFormat::PNG);

if (ImageWrapper.IsValid() && ImageWrapper->SetCompressed(RawFileData.GetData(), RawFileData.Num()))
{
    const TArray<uint8>* UncompressedRGBA = nullptr;

    // ERGBFormat::BGRA 为 RGB 的格式
    // 第二个参数为通道的位深度，通常为 8
    // UncompressedRGBA 保存了uncompressed raw data.
    if (ImageWrapper->GetRaw(ERGBFormat::BGRA, 8, UncompressedRGBA))
    {
        /* 执行接下来的操作 */
    }
}

生成空的 Texture

首先我们要确定想要生成的 Texture 所在的位置，也就是要确定 Package 的位置，也就是确定 Path：

image-20210812142156093.png

Package 的位置由 MountPoint 开始，这个 MountPoint 就是类似 /Game、/Engine 这样的东西；

如果我们需要 在指定目录保存这些文件，比如我们不想在 /Game、/Engine 的目录写入这些信息，想在自己的插件目录、其它本地目录保存，那么我们需要先注册 MountPoint：

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// Register mount point to save assets
FPackageName::RegisterMountPoint("/你想的 MountPoint 名字/",  对应的路径);

接着我们：

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const FString PackageName = MountPointName + TEXT("/textures/") + ImageName;

UPackage* TexturePackage = CreatePackage(nullptr, *PackageName);
TexturePackage->FullyLoad();

Texture = NewObject<UTexture2D>(TexturePackage, FName(*ImageName), RF_Public | RF_Standalone | RF_MarkAsRootSet);

将数据写入 Texture 中

我们生成的空 Texture 会默认采用 Mipmap 压缩，但是显然这不一定合理。

如果 边长 不是 2 的幂次方，则不能使用 Mipmap 压缩，否则会出现错误，我们可以用 x & (x - 1) 来判断 x 是否是 2 的幂次方，如果 x & (x - 1) == 0 则说明是，否则不是 。

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int32 SizeX = ImageWrapper->GetWidth();
int32 SizeY = ImageWrapper->GetHeight();
const EPixelFormat PixelFormat = PF_B8G8R8A8;
int32 PixelSize = SizeX * SizeY * GPixelFormats[PixelFormat].BlockBytes;
// PixelSize 计算了所有的像素信息一共占了多少空间

if (SizeX > 0 && SizeY > 0 && (SizeX % GPixelFormats[PixelFormat].BlockSizeX) == 0 && (SizeY % GPixelFormats[PixelFormat].BlockSizeY) == 0)
{
   		/* 先生成一个空的 Texture */

    // 更新 Texture 的 PlatformData
    Texture->PlatformData = new FTexturePlatformData();
    Texture->PlatformData->SizeX = SizeX;
    Texture->PlatformData->SizeY = SizeY;
    Texture->PlatformData->NumSlices = 1;
    Texture->PlatformData->PixelFormat = PixelFormat;

    // 判断边长是否是 2 的幂次方，如果当前的边长不是 2 的幂次方的时候，不开启 Mipmap 压缩
    if ( (SizeX & (SizeX - 1) || (SizeY & (SizeY - 1))) )
        Texture->MipGenSettings = TextureMipGenSettings::TMGS_NoMipmaps;

    // 分配第一个 Mip
    FTexture2DMipMap* Mip = new FTexture2DMipMap();
    Texture->PlatformData->Mips.Add(Mip);
    Mip->SizeX = SizeX;
    Mip->SizeY = SizeY;

    // 向 Mip 的 Bulkdata 中写入数据，注意先加上锁
    Mip->BulkData.Lock(LOCK_READ_WRITE);
    uint8* TextureData = (uint8*) Mip->BulkData.Realloc(PixelSize);
    FMemory::Memcpy(TextureData, UncompressedRGBA->GetData(), PixelSize);
    Mip->BulkData.Unlock();

    // 初始化 Texture 的信息，完成数据的临时写入，也就是可选保存的状态
    Texture->Source.Init(SizeX, SizeY, 1, 1, ETextureSourceFormat::TSF_BGRA8, UncompressedRGBA->GetData());
    Texture->UpdateResource();
}

保存资源

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// Create Assets
TexturePackage->MarkPackageDirty();
FAssetRegistryModule::AssetCreated(Texture);

// 获取 Package 的文件名
FString PackageFileName = FPackageName::LongPackageNameToFilename(PackageName, FPackageName::GetAssetPackageExtension());

// 保存资源
UPackage::SavePackage(TexturePackage, Texture, EObjectFlags::RF_Public | EObjectFlags::RF_Standalone, *PackageFileName);

完整代码

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UTexture2D* CreateTexture()
{
	UTexture2D* Texture = nullptr;

	const FString PicturePath = ImageDirectory.Path + TEXT("/") + ImageName + TEXT(".png");
	
	if (!FPlatformFileManager::Get().GetPlatformFile().FileExists(*PicturePath))
	{
		return nullptr;
	}
	
	const FString PackageName = MountPointName + TEXT("/textures/") + ImageName;

	// Read loacl PNG to Texture

	TArray<uint8> RawFileData;
	if (!FFileHelper::LoadFileToArray(RawFileData, *PicturePath))
	{
		return nullptr;
	}
	
	IImageWrapperModule& ImageWrapperModule = FModuleManager::LoadModuleChecked<IImageWrapperModule>("ImageWrapper");

	TSharedPtr<IImageWrapper> ImageWrapper = ImageWrapperModule.CreateImageWrapper(EImageFormat::PNG);

	if (ImageWrapper.IsValid() && ImageWrapper->SetCompressed(RawFileData.GetData(), RawFileData.Num()))
	{
		const TArray<uint8>* UncompressedRGBA = nullptr;
		if (ImageWrapper->GetRaw(ERGBFormat::BGRA, 8, UncompressedRGBA))
		{
			int32 SizeX = ImageWrapper->GetWidth();
			int32 SizeY = ImageWrapper->GetHeight();
			const EPixelFormat PixelFormat = PF_B8G8R8A8;
			int32 PixelSize = SizeX * SizeY * GPixelFormats[PixelFormat].BlockBytes;
			
			if (SizeX > 0 && SizeY > 0 && (SizeX % GPixelFormats[PixelFormat].BlockSizeX) == 0 && (SizeY % GPixelFormats[PixelFormat].BlockSizeY) == 0)
			{
				// Create new texture pointer			
				UPackage* TexturePackage = CreatePackage(nullptr, *PackageName);
				TexturePackage->FullyLoad();
				Texture = NewObject<UTexture2D>(TexturePackage, FName(*ImageName), RF_Public | RF_Standalone | RF_MarkAsRootSet);

				Texture->PlatformData = new FTexturePlatformData();
				Texture->PlatformData->SizeX = SizeX;
				Texture->PlatformData->SizeY = SizeY;
				Texture->PlatformData->NumSlices = 1;
				Texture->PlatformData->PixelFormat = PixelFormat;

				// Determine whether it is a power of 2 to use mipmap
				if ( (SizeX & (SizeX - 1) || (SizeY & (SizeY - 1))) )
					Texture->MipGenSettings = TextureMipGenSettings::TMGS_NoMipmaps;
				
				// Allocate first mipmap.
				FTexture2DMipMap* Mip = new FTexture2DMipMap();
				Texture->PlatformData->Mips.Add(Mip);
				Mip->SizeX = SizeX;
				Mip->SizeY = SizeY;

				// Lock the texture so that it can be modified
				Mip->BulkData.Lock(LOCK_READ_WRITE);
				uint8* TextureData = (uint8*) Mip->BulkData.Realloc(PixelSize);
				FMemory::Memcpy(TextureData, UncompressedRGBA->GetData(), PixelSize);
				Mip->BulkData.Unlock();

				Texture->Source.Init(SizeX, SizeY, 1, 1, ETextureSourceFormat::TSF_BGRA8, UncompressedRGBA->GetData());
				Texture->UpdateResource();

				// Create Assets
				TexturePackage->MarkPackageDirty();
				
				FAssetRegistryModule::AssetCreated(Texture);

				FString PackageFileName = FPackageName::LongPackageNameToFilename(PackageName, FPackageName::GetAssetPackageExtension());

				UPackage::SavePackage(TexturePackage, Texture, EObjectFlags::RF_Public | EObjectFlags::RF_Standalone, *PackageFileName);
			}
		}
	}

	return Texture; 
}

参考源码

EditorFactories : UTextureFactory::ImportTexture()：实现了从外部导入图片生成 Texture

Texture2D : UTexture2D::CreateTransient()：实现了生成一个临时性的 Texture2D 文件

Texture : FTextureSource::GetMipData()：实现了获取 Texture 中 Mip 的数据

Texture2D -> PNG

分析

  1. 修改 Texture 的设置
  2. 读取像素信息并生成图片

修改 Texture 的设置

在原本 Texture 的设置下，我们可能无法从 BulkData 读取出信息，会返回一个空指针，所以我们需要先修改一下 Texture 的设置；同时记录一下原本的设置，用于之后的复原。

CompressionSettings 设置为 TC_VectorDisplacementmap

MipGenSettings 设置为 TMGS_NoMipmaps

SRGB 设置为 false

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// 记录原本的设置信息
TextureCompressionSettings OldCompressionSettings = Texture->CompressionSettings;
TextureMipGenSettings OldMipGenSettings = Texture->MipGenSettings;
bool OldSRGB = Texture->SRGB;

// 修改设置
Texture->CompressionSettings = TextureCompressionSettings::TC_VectorDisplacementmap;
Texture->MipGenSettings = TextureMipGenSettings::TMGS_NoMipmaps;
Texture->SRGB = false;
Texture->UpdateResource();

	/* 读取信息 */

// 复原回原本的设置
Texture->CompressionSettings = OldCompressionSettings;
Texture->MipGenSettings = OldMipGenSettings;
Texture->SRGB = OldSRGB;
Texture->UpdateResource();

读取像素信息并生成图片

我们从 Texture 的 Platform 中读取出 Mip 的 BulkData，然后对其进行映射，将信息映射到 PixelColor 中

image-20210812145950820

每一个 PixelColor 包含着 BGRA 的信息，多个 PixelColor 组成了数组 ColorData；

接着依赖于 ImageUtils ，我们压缩这个 ColorData 生成 ImageData，并将其写入指定位置，就可以生成出 png 图片。

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// export texture to image
FTexture2DMipMap& Mip = Texture->PlatformData->Mips[0];
uint8* TextureData = (uint8*) Mip.BulkData.Lock(LOCK_READ_WRITE);
Mip.BulkData.Unlock();

int32 SizeX = Texture->PlatformData->SizeX;
int32 SizeY = Texture->PlatformData->SizeY;
TArray<FColor> ColorData;
for (int32 IndexY = 0; IndexY < SizeY; IndexY++)
{
    for (int32 IndexX = 0; IndexX < SizeX; IndexX++)
    {
        FColor PixelColor;
        PixelColor.B = TextureData[(IndexY * SizeX + IndexX) * 4 + 0];
        PixelColor.G = TextureData[(IndexY * SizeX + IndexX) * 4 + 1];
        PixelColor.R = TextureData[(IndexY * SizeX + IndexX) * 4 + 2];
        PixelColor.A = TextureData[(IndexY * SizeX + IndexX) * 4 + 3];
        ColorData.Add(PixelColor);
    }
}

TArray<uint8> ImageData;
FImageUtils::CompressImageArray(SizeX, SizeY, ColorData, ImageData);
FFileHelper::SaveArrayToFile(ImageData, *PicturePath);

完整代码

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void WriteTexture(UTexture2D* Texture)
{
	FString PicturePath = ExportImageDirectory.Path + TEXT("/") + Texture->GetName() + TEXT(".png");

	// record old settings
	TextureCompressionSettings OldCompressionSettings = Texture->CompressionSettings;
	TextureMipGenSettings OldMipGenSettings = Texture->MipGenSettings;
	bool OldSRGB = Texture->SRGB;

	// modified to exportable settings
	Texture->CompressionSettings = TextureCompressionSettings::TC_VectorDisplacementmap;
	Texture->MipGenSettings = TextureMipGenSettings::TMGS_NoMipmaps;
	Texture->SRGB = false;
	Texture->UpdateResource();

	// export texture to image
	FTexture2DMipMap& Mip = Texture->PlatformData->Mips[0];
	uint8* TextureData = (uint8*) Mip.BulkData.Lock(LOCK_READ_WRITE);
	Mip.BulkData.Unlock();
	
	int32 SizeX = Texture->PlatformData->SizeX;
	int32 SizeY = Texture->PlatformData->SizeY;
	TArray<FColor> ColorData;
	for (int32 IndexY = 0; IndexY < SizeY; IndexY++)
	{
		for (int32 IndexX = 0; IndexX < SizeX; IndexX++)
		{
			FColor PixelColor;
			PixelColor.B = TextureData[(IndexY * SizeX + IndexX) * 4 + 0];
			PixelColor.G = TextureData[(IndexY * SizeX + IndexX) * 4 + 1];
			PixelColor.R = TextureData[(IndexY * SizeX + IndexX) * 4 + 2];
			PixelColor.A = TextureData[(IndexY * SizeX + IndexX) * 4 + 3];
			ColorData.Add(PixelColor);
		}
	}

	TArray<uint8> ImageData;
	FImageUtils::CompressImageArray(SizeX, SizeY, ColorData, ImageData);
	FFileHelper::SaveArrayToFile(ImageData, *PicturePath);

	// return to old settings
	Texture->CompressionSettings = OldCompressionSettings;
	Texture->MipGenSettings = OldMipGenSettings;
	Texture->SRGB = OldSRGB;
	Texture->UpdateResource();
}

参考源码

GameViewportClient : UGameViewportClient::ProcessScreenShots()：实现了导出屏幕截图

Sprite -> PNG

分析

首先我们来看一下 Sprite 的信息：

image-20210812150627183

其中，SourceUV 切割出的图片，左上角的偏移量；Source Dimension 表示切割图片的大小；SourceTexture 表示从哪个 Texture 切割而来。

举个例子：

image-20210812231527306

在这幅图中，Texture->PlatformData->SizeX = 9、Texture->PlatformData->SizeY = 5，

假设我们切割的是红色部分，则 SourceUV = (3, 1) 、SourceDimension = (4, 3)，此时的偏移量应该是 9(第一行) + 3(第二行空白处) = 12

我们发现 PaperSprite 中预留了这个函数，可以让我们获取到这三个信息：

image-20210812150952019

这下子就很明确了，我们拿到这些信息，通过计算偏移量，就可以从 SourceTexture 中切割出图片来，剩下的内容和 Texture -> PNG 就一样了。

还一些需要注意的是，记得包含 PaperSpriteComponent.h、PaperSprite.h，如果在插件中使用 Sprite，需要依赖模块 Paper2D。

完整代码

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void WriteSprite(UPaperSprite* Sprite)
{
	FString PicturePath = ExportImageDirectory.Path + TEXT("/") + Sprite->GetName() + TEXT(".png");

	// record old settings
	UTexture2D* Texture = Sprite->GetSourceTexture();
	
	TextureCompressionSettings OldCompressionSettings = Texture->CompressionSettings;
	TextureMipGenSettings OldMipGenSettings = Texture->MipGenSettings;
	bool OldSRGB = Texture->SRGB;

	// modified to exportable settings
	Texture->CompressionSettings = TextureCompressionSettings::TC_VectorDisplacementmap;
	Texture->MipGenSettings = TextureMipGenSettings::TMGS_NoMipmaps;
	Texture->SRGB = false;
	Texture->UpdateResource();

	// export texture to image
	FTexture2DMipMap& Mip = Texture->PlatformData->Mips[0];
	uint8* TextureData = (uint8*) Mip.BulkData.Lock(LOCK_READ_WRITE);
	Mip.BulkData.Unlock();

	// 切割 Sprite，计算偏移量
	FVector2D SourceUV = Sprite->GetSourceUV();
	FVector2D SourceSize = Sprite->GetSourceSize();
	
	int32 SizeX = (int32)SourceSize.X;
	int32 SizeY = (int32)SourceSize.Y;
	int32 Offsets = (int32)SourceUV.Y * Texture->PlatformData->SizeX + (int32)SourceUV.X;

	
	TArray<FColor> ColorData;
	for (int32 IndexY = 0; IndexY < SizeY; IndexY++)
	{
		for (int32 IndexX = 0; IndexX < SizeX; IndexX++)
		{
			FColor PixelColor;
			PixelColor.B = TextureData[(IndexY * Texture->PlatformData->SizeX + IndexX + Offsets) * 4 + 0];
			PixelColor.G = TextureData[(IndexY * Texture->PlatformData->SizeX + IndexX + Offsets) * 4 + 1];
			PixelColor.R = TextureData[(IndexY * Texture->PlatformData->SizeX + IndexX + Offsets) * 4 + 2];
			PixelColor.A = TextureData[(IndexY * Texture->PlatformData->SizeX + IndexX + Offsets) * 4 + 3];
			ColorData.Add(PixelColor);
		}
	}

	TArray<uint8> ImageData;
	FImageUtils::CompressImageArray(SizeX, SizeY, ColorData, ImageData);
	FFileHelper::SaveArrayToFile(ImageData, *PicturePath);

	// return to old settings
	Texture->CompressionSettings = OldCompressionSettings;
	Texture->MipGenSettings = OldMipGenSettings;
	Texture->SRGB = OldSRGB;
	Texture->UpdateResource();
}