UE4 场景中截取图片并保存（C++实现）

在UE4中，你可以使用C++代码来实现截取场景中的图片并保存到本地。具体步骤如下：

1. 创建一个C++类，并继承自AActor类。命名为"ScreenshotActor"。

2. 在"ScreenshotActor.h"文件中添加以下头文件：

#include "Engine/Engine.h"
#include "Kismet/GameplayStatics.h"
#include "Engine/GameViewportClient.h"
#include "Misc/FileHelper.h"
#include "Misc/Paths.h"

3. 在"ScreenshotActor.h"文件中添加以下声明：

UCLASS()
class YOURPROJECT_API AScreenshotActor : public AActor
{
    GENERATED_BODY()

public:
    // Sets default values for this actor's properties
    AScreenshotActor();

    // Take screenshot and save to file
    UFUNCTION(BlueprintCallable, Category = "Screenshot")
    void TakeScreenshot();

private:
    // The resolution multiplier for the screenshot
    UPROPERTY(EditAnywhere, Category = "Screenshot")
    int32 ResolutionMultiplier = 1;
};

4. 在"ScreenshotActor.cpp"文件中添加以下代码：

#include "ScreenshotActor.h"

AScreenshotActor::AScreenshotActor()
{
    PrimaryActorTick.bCanEverTick = false;
}

void AScreenshotActor::TakeScreenshot()
{
    // Get the game viewport client
    UGameViewportClient* ViewportClient = GEngine->GameViewport;
    if (ViewportClient)
    {
        // Get the viewport size
        FVector2D Size;
        ViewportClient->GetViewportSize(Size);

        // Calculate the screenshot resolution
        int32 ResolutionX = Size.X * ResolutionMultiplier;
        int32 ResolutionY = Size.Y * ResolutionMultiplier;

        // Take the screenshot
        TArray<FColor> Bitmap;
        Bitmap.AddUninitialized(ResolutionX * ResolutionY);
        ViewportClient->ReadPixels(Bitmap);

        // Create the screenshot texture
        UTexture2D* Screenshot = UTexture2D::CreateTransient(ResolutionX, ResolutionY);
        Screenshot->CompressionSettings = TC_HDR;
        Screenshot->SRGB = false;
        Screenshot->AddToRoot();
        Screenshot->UpdateResource();

        // Copy the pixel data to the texture
        uint8* MipData = static_cast<uint8*>(Screenshot->PlatformData->Mips[0].BulkData.Lock(LOCK_READ_WRITE));
        FMemory::Memcpy(MipData, Bitmap.GetData(), Bitmap.Num() * sizeof(FColor));
        Screenshot->PlatformData->Mips[0].BulkData.Unlock();

        // Save the screenshot to file
        FDateTime Now = FDateTime::Now();
        FString Filename = FString::Printf(TEXT("Screenshot_%04d%02d%02d_%02d%02d%02d.png"), Now.GetYear(), Now.GetMonth(), Now.GetDay(), Now.GetHour(), Now.GetMinute(), Now.GetSecond());
        FString SaveDirectory = FPaths::GameSavedDir() + TEXT("Screenshots/");
        if (!FPaths::DirectoryExists(SaveDirectory))
        {
            FPlatformFileManager::Get().GetPlatformFile().CreateDirectory(*SaveDirectory);
        }
        FString FilePath = SaveDirectory + Filename;
        FFileHelper::SaveArrayToFile(Screenshot->GetRawImageData(), Screenshot->GetAllocatedSize(), *FilePath);

        // Remove the screenshot texture
        Screenshot->RemoveFromRoot();
    }
}

5. 在UE4编辑器中创建一个蓝图，并选择"ScreenshotActor"作为其父类。

6. 在蓝图中添加一个"Take Screenshot"函数，并调用AScreenshotActor::TakeScreenshot()函数。

7. 在场景中放置该蓝图，并运行游戏。当需要截取场景中的图片时，调用蓝图中的"Take Screenshot"函数即可。

注意：在截图之前需要确保场景中的所有元素都已经加载完毕，否则可能会导致截图不完整或者出现其他问题。另外，该实现只适用于PC平台，如果需要支持其他平台，请参考UE4官方文档或者相关论坛。