UE4 Loading Screen with Progress

README.md

This will only work in cooked builds with Event Driven Loader enabled (enabled by default). Currently this only shows the specified packages loading progress, but not dependant packages, which is an annoying issue since that is where most of the loading time is for maps.

TestGameInstance.cpp

#include "TestGameInstance.h"
#include "MoviePlayer/Public/MoviePlayer.h"
#include "Widgets/SCompoundWidget.h"
#include "Widgets/Text/STextBlock.h"
#include "Widgets/SBoxPanel.h"

class STestLoadingScreen : public SCompoundWidget
{
public:
	SLATE_BEGIN_ARGS(STestLoadingScreen) 
	: _InMap()
	{}
	SLATE_ARGUMENT(FName, InMap)
	SLATE_END_ARGS()

	void Construct(const FArguments& InArgs)
	{
		InMap = InArgs._InMap;
		
		ChildSlot
		[
			SNew(SVerticalBox)
			+ SVerticalBox::Slot()
			.VAlign(VAlign_Center)
			.HAlign(HAlign_Center)
			[
				SNew(STextBlock)
				.Font(FCoreStyle::GetDefaultFontStyle("Regular", 64))
				.Text(this, &STestLoadingScreen::GetMessage)
				.Visibility(this, &STestLoadingScreen::GetMessageIndicatorVisibility)
			]
		];
	}

private:
	FName InMap;

	FText GetMessage() const
	{
		float LoadPercentage = GetAsyncLoadPercentage(InMap);

		if (LoadPercentage < 0)
		{
			LoadPercentage = 100.f;
		}

		return FText::FromString(FString::Printf(TEXT("%d%%"), FMath::TruncToInt(LoadPercentage)));
	}

	EVisibility GetMessageIndicatorVisibility() const
	{
		return EVisibility::Visible;
	}
};

void UTestGameInstance::Init()
{
	Super::Init();

	FCoreUObjectDelegates::PreLoadMap.AddUObject(this, &UTestGameInstance::BeginLoadingScreen);
}

void UTestGameInstance::BeginLoadingScreen(const FString& MapName)
{
	if (IsRunningDedicatedServer())
	{
		return;
	}

	FLoadingScreenAttributes LoadingScreen;
	LoadingScreen.bAutoCompleteWhenLoadingCompletes = false;
	LoadingScreen.bWaitForManualStop = false;
	LoadingScreen.bMoviesAreSkippable = false;
	LoadingScreen.WidgetLoadingScreen = SNew(STestLoadingScreen).InMap(FName(*MapName));
	LoadingScreen.PlaybackType = EMoviePlaybackType::MT_LoadingLoop;

	GetMoviePlayer()->SetupLoadingScreen(LoadingScreen);
	GetMoviePlayer()->PlayMovie();
}

TestGameInstance.h

#pragma once

#include "Test.h"
#include "CoreMinimal.h"
#include "Engine/GameInstance.h"
#include "TestGameInstance.generated.h"

UCLASS(config=Game)
class TEST_API UTestGameInstance : public UGameInstance
{
	GENERATED_BODY()
	
public:
	virtual void Init() override;
	
	void BeginLoadingScreen(const FString& MapName);
};

It won't work now because FAsyncLoadingThread2::GetAsyncLoadPercentage will always return -1.0f, unfortunately. Overall, these techniques won't work with World Partition either, the only more or less reliable technique is to count actors being registered and update the list when the next ULevelStreaming is loaded. But it's very tricky.