UE4引擎实现隐藏UI截图拍照并保存到iOS系统相册

需求

Unreal engine隐藏UI截图后保存到系统（iPad）相册

思路

1. plist中添加相册相关权限
2. 使用UE截图API获取无UI截图，并保存到项目临时目录
3. 混编Objective-c原生代码将临时文件复制到系统相册

开发步骤

1.配置plist权限

修改UE配置，位置在：UE引擎>编辑>项目设置>平台>iOS>Extra PList Data>Additional Plist Data
当然也可以直接搜索Additional Plist Data

将下面的配置追加到原有配置里

<key>NSPhotoLibraryUsageDescription</key><string>需要相册权限以保存截图</string>

2.写代码

实现保存iOS相册

c++是可以与objectivec混编的，可以将原生代码直接写到cpp文件中，在UE中可以使用#if PLATFORM_IOS宏来区分平台。

Screenshooter.h

#pragma once

#if PLATFORM_IOS
#import <UIKit/UIKit.h>

@interface Screenshooter : UIViewController <UINavigationControllerDelegate>
+ (void) saveScreenshotNative;
@end

#endif

#include "GameFramework/Actor.h"
#include "Screenshooter.generated.h"

UCLASS()
class AScreenshooter : public AActor
{
    GENERATED_BODY()
public:
    AScreenshooter();
    UFUNCTION()
    void onOk();
};

Screenshooter.cpp

#include "Screenshooter.h"
#include "Misc/Paths.h"
#include "UnrealClient.h"
#include <pch.h>
#if PLATFORM_IOS
    #include "IOSAppDelegate.h"
    #import <Foundation/Foundation.h>
#endif



#if PLATFORM_IOS

@interface Screenshooter()
@end

@implementation Screenshooter
 + (Screenshooter*)GetDelegate
 {
    static Screenshooter* Singleton = [[Screenshooter alloc] init];
    return Singleton;
 }

- (void)saveShot
{
    NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
    NSString *documentsDirectory = [paths objectAtIndex:0];
    NSString *filePath = [documentsDirectory stringByAppendingPathComponent:@"/Game/Saved/Screenshots/IOS/screenshot.png"];
    UIImage *image = [UIImage imageWithContentsOfFile:filePath];
    UIImageWriteToSavedPhotosAlbum(image, nil, nil, nil);
}

+ (void)saveScreenshotNative
{
    [[Screenshooter GetDelegate] performSelectorOnMainThread:@selector(saveShot) withObject:nil waitUntilDone : NO];
}

@end
#endif

AScreenshooter::AScreenshooter()
{
}

void AScreenshooter::onOk() {
    #if PLATFORM_IOS
    [Screenshooter saveScreenshotNative];
    //FPlatformFileManager::Get().GetPlatformFile().DeleteFile(*screenshot_path);
    #endif
}

截屏实现

头文件

#include "Screenshooter.h"
//...
    public:
        AScreenshooter* m_Screenshooter;
        void OnClickPrtScreenButton();
//...

相关逻辑

//初始化AScreenshooter
void UInGameWidget::OnStart()
{
    m_Screenshooter = NewObject<AScreenshooter>();
}
//...
//实现拍照
void UInGameWidget::OnClickPrtScreenButton() {
    FScreenshotRequest::OnScreenshotRequestProcessed().AddUObject(m_Screenshooter, &AScreenshooter::onOk);
    FScreenshotRequest::RequestScreenshot(TEXT("screenshot.png"),false, false);
}
//...

3.Debug或打包

略

参考资料
https://docs.unrealengine.com/latest/INT/API/Runtime/Engine/FScreenshotRequest/index.html
https://answers.unrealengine.com/questions/164650/how-to-access-ios-photo-library.html
https://answers.unrealengine.com/questions/393721/screenshot-on-ios-dont-show-in-ipad-gallery.html