UnrealEngineUWP/Engine/Source/Runtime/PreLoadScreen/Public/PreLoadScreen.h

// Copyright 1998-2019 Epic Games, Inc. All Rights Reserved.

#pragma once

#include "Widgets/SWindow.h"

enum class EPreLoadScreenTypes : uint8
{
    EarlyStartupScreen,
    EngineLoadingScreen
};

// Interface that defines the class that handles all the logic for controlling / displaying a particular PreLoadScreen.
// Designed to be implemented in a Plugin that calls FPreLoadScreenManager::RegisterPreLoadScreen so that functions are called by PreLoadScreenManager correctly.
// Really should probably inherit from FPreLoadScreenBase instead of this class for more functionality
class IPreLoadScreen //: public TSharedFromThis<IPreLoadScreen, ESPMode::ThreadSafe>
{
public:
    virtual ~IPreLoadScreen() {};

    virtual void Init() = 0;
    
    //Standard tick that happens every frame
    virtual void Tick(float DeltaTime) = 0;

    //This function is used to determine if an extra platform sleep should be performed every tick (to slow down the tick rate)
    //keeps us from spinning super fast when we aren't doing much beyond loading data / etc on other threads.
    virtual float GetAddedTickDelay() = 0;

    //This tick happens as part of the slate render tick during an EarlyStartupLoadScreen
    virtual void RenderTick(float DeltaTime) = 0;
    
    //Callback for when a PreLoadScreen starts being displayed. Provides a reference to the SWindow that will be used to display content
    virtual void OnPlay(TWeakPtr<SWindow> TargetWindow) = 0;

    //Callback for when a PreLoadScreen is no longer being displayed.
    virtual void OnStop() = 0;
    
    virtual bool IsDone() const = 0;

    virtual void CleanUp() = 0;

    //Should override this function to determine if this screen should be used to handle EarlyStartupScreen behavior
    //IMPORTANT: This changes a LOT of functionality and implementation details. EarlyStartupScreens happen before the engine is fully initialized and block engine initialization before they finish.
    //           this means they have to forgo even the most basic of engine features like UObject support, as they are displayed before those systems are initialized.
    virtual EPreLoadScreenTypes GetPreLoadScreenType() const = 0;

	// Allows the PreLoadScreen to register a tag that can be later used to find a specific loading screen. 
	// PreLoadScreens not using this functionality should return NAME_None
	virtual FName GetPreLoadScreenTag() const = 0;

    virtual void SetEngineLoadingFinished(bool IsEngineLoadingFinished) = 0;

    virtual const TSharedPtr<const SWidget> GetWidget() const = 0;
    virtual TSharedPtr<SWidget> GetWidget() = 0;
};