LevelStreamingDelegates.h

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// Copyright Epic Games, Inc. All Rights Reserved.
// Globally-bound delegates for level streaming status updates
 
#pragma once
 
#include "Delegates/Delegate.h"
 
class UWorld;
class ULevelStreaming;
class ULevel;
 
enum class ELevelStreamingState : uint8;
enum class ELevelStreamingTargetState : uint8;
 
// TODO: what is the best way to capture a level which is queued for unload while it is during async load or add to world?
//  Are level async loads actually cancelled?
 
struct FLevelStreamingDelegates
{
    // Called when a new target state for a streaming level is determined. 
    // Can be used to measure latency between requests and application
    // (e.g. limits on current level loads & visibility changes)
    static ENGINE_API TMulticastDelegate<void(
        UWorld*, 
        const ULevelStreaming*, 
        ULevel* LevelIfLoaded,
        ELevelStreamingState Current,
        ELevelStreamingTargetState PrevTarget, 
        ELevelStreamingTargetState NewTarget)> OnLevelStreamingTargetStateChanged;
 
    // Called when a streaming level enters a new state.
    // When a level is newly added to the streaming system, PreviousState and NewState may be equal.
    static ENGINE_API TMulticastDelegate<void(
        UWorld*, 
        const ULevelStreaming*,
        ULevel* LevelIfLoaded,
        ELevelStreamingState PreviousState,
        ELevelStreamingState NewState
        )> OnLevelStreamingStateChanged;
 
    // Notifications on when work actually beings on making a level visible or invisible, so profiling tools can measure the difference between time spent waiting to be added to the world and time spend actively working
    static ENGINE_API TMulticastDelegate<void(UWorld*, const ULevelStreaming*, ULevel* LoadedLevel)> OnLevelBeginMakingVisible;
    static ENGINE_API TMulticastDelegate<void(UWorld*, const ULevelStreaming*, ULevel* LoadedLevel)> OnLevelBeginMakingInvisible;
};