UE4 创建一个actor，具有截图保存功能（C++实现）

可以参考以下步骤来创建一个具有截图保存功能的Actor：

1. 首先创建一个继承自Actor的子类，并在头文件中添加以下include语句：

#include "Engine/TextureRenderTarget2D.h"
#include "EngineUtils.h"

2. 在子类中添加以下成员变量：

UPROPERTY(EditAnywhere)
int32 Width = 1024;

UPROPERTY(EditAnywhere)
int32 Height = 1024;

UPROPERTY(EditAnywhere)
FString SavePath = FPaths::ProjectSavedDir() + "Screenshots/";

UPROPERTY(EditAnywhere)
FString FileNamePrefix = "Screenshot_";

这些变量将控制截图的大小、保存路径和文件名前缀。

3. 在子类中添加以下函数：

void SaveScreenshot(UTextureRenderTarget2D* RenderTarget, const FString& FilePath);

FString GetUniqueFilename(const FString& Prefix, const FString& Extension);

SaveScreenshot函数将保存截图到指定路径，GetUniqueFilename函数将生成一个唯一的文件名。

4. 在子类的cpp文件中实现以上两个函数：

void AMyActor::SaveScreenshot(UTextureRenderTarget2D* RenderTarget, const FString& FilePath)
{
    TArray<FColor> Bitmap;
    FIntRect Rect(0, 0, RenderTarget->SizeX, RenderTarget->SizeY);
    RenderTarget->ReadPixels(Bitmap, FReadSurfaceDataFlags(), Rect);

    FString Filename = GetUniqueFilename(FileNamePrefix, ".png");
    FString FullPath = FilePath + Filename;

    FFileHelper::CreateDirectory(*FilePath);
    FSaveImageDialog::SaveImage(FullPath, Rect.Width(), Rect.Height(), Bitmap.GetData(), nullptr);
}

FString AMyActor::GetUniqueFilename(const FString& Prefix, const FString& Extension)
{
    FString Filename;
    int32 Number = 0;

    do
    {
        Filename = Prefix + FString::FromInt(Number++) + Extension;
    } while (FPlatformFileManager::Get().GetPlatformFile().FileExists(*Filename));

    return Filename;
}

5. 在子类中添加以下函数：

void CaptureScreenshot();

这个函数将截图并保存到指定路径。

6. 在子类的cpp文件中实现CaptureScreenshot函数：

void AMyActor::CaptureScreenshot()
{
    UWorld* World = GetWorld();
    if (!World)
    {
        return;
    }

    TArray<AActor*> Actors;
    UGameplayStatics::GetAllActorsOfClass(World, APlayerController::StaticClass(), Actors);
    if (Actors.Num() == 0)
    {
        return;
    }

    APlayerController* PlayerController = Cast<APlayerController>(Actors[0]);
    if (!PlayerController)
    {
        return;
    }

    ULocalPlayer* LocalPlayer = Cast<ULocalPlayer>(PlayerController->Player);
    if (!LocalPlayer)
    {
        return;
    }

    UTextureRenderTarget2D* RenderTarget = NewObject<UTextureRenderTarget2D>();
    RenderTarget->ClearColor = FLinearColor::Black;
    RenderTarget->InitAutoFormat(Width, Height);
    RenderTarget->UpdateResourceImmediate();

    FViewport Viewport(0, 0, Width, Height);
    FSceneViewFamilyContext ViewFamily(FSceneViewFamily::ConstructionValues(
        Viewport,
        World->Scene,
        LocalPlayer->ViewportClient->EngineShowFlags)
        .SetRealtimeUpdate(true));
    FSceneView* View = LocalPlayer->CalcSceneView(&ViewFamily);
    View->ViewRect = FIntRect(0, 0, Width, Height);
    View->UpdateViewMatrix();
    View->SetScreenPercentage(100.0f);

    FTextureRenderTargetResource* RenderTargetResource = RenderTarget->GameThread_GetRenderTargetResource();
    View->Family->RenderInterface->Render(View, FTextureRHIRef(), FTextureRHIRef(), RenderTargetResource->GetRenderTargetTexture(), View->ViewRect, false);

    SaveScreenshot(RenderTarget, SavePath);
}

这个函数使用场景中的第一个PlayerController来获取场景视图，并将其渲染到一个RenderTarget上，然后调用SaveScreenshot函数保存截图。

7. 最后，可以在Actor的BeginPlay函数中调用CaptureScreenshot函数来测试截图功能：

void AMyActor::BeginPlay()
{
    Super::BeginPlay();

    CaptureScreenshot();
}

这样就完成了一个具有截图保存功能的Actor。