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> Programming and Scripting > Blueprint Visual Scripting > Specialized Node Groups > Timelines > Fading Lights

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Fading Lights

An example use of a timeline in which we set up a fading light that also changes color.

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C++

This document describes how to set up a light Actor that changes color and slowly fades away on contact.

This will be done using a Point Light Component containing a Box Component to serve as an overlap trigger and a Timeline component to manipulate the Point Light Actor.

Creating the Fading Light Actor

Begin by creating a New > Games > Blank > Blueprint project named FadingLights.
Click the Add/Import button to create a new Blueprint Actor class named BP_LightActor.
Double-click the BP_LightActor from the Content Browser to open it in the Blueprint Editor and open the Class Defaults.
Click Add Component, select Box Collision from the dropdown menu, and rename it to OverlapCollision.
From the Components tab, select and drag the overlap collision onto the DefaultSceneRoot to make OverlapCollision the new Root Component.
Click Add Component, search and select Point Light.
Open the Event Graph, right-click the graph, and choose Add Timeline from the Blueprint Context Menu. Name the Timeline PointLightTimeline.
Navigate to the My Blueprint tab and from the Variables category, click the + Variable button to add a new variable of type float. Name the variable BrightnessMultiplier, compile and set its Default Value to 20.0.
Compile and Save.

Setting Up the Brightness Track

When the player overlaps with the light Actor's box component bounds, the Timeline component will require a float curve to manipulate the point light component's brightness value.

The luminosity will have an initial value of 5000 and will decrease to 0 over the span of 5 seconds.

Double-click the PointLightTimeline node to open the Timeline Editor and add a float curve track.
Name the float curve track LightBrightnessFloatTrack, and shift-click to add two keys to the track. Assign one key a time-value (0,5000), and the other key a time-value of (5,0).
The completed LightBrightnessFloat track will appear as it does below.

Setting Up The Color Track

When the player overlaps with the light Actor's box component bounds, the PointLight Timeline will require a linear color curve track to manipulate the point light component's color property.

From the Timeline Editor add a color curve track.
Name the new color track LightLinearColorTrack.
Double-click the first color key to modify it with a time of 0, and RGB value of: (R:1,G:0.665,B:0.015).
Modify the second color key with a time of 5, and RGB value of: (R:0,G:0,B:0).
Compile and Save the Blueprint.
Your completed color track will appear as it does below.

Work-In-Progress Blueprint

Creating the Collision Overlap Event and Update Logic

The Box Component requires the ability to trigger the TimelineComponent when an Actor enters its collision bounds.

Additionally, the PointLightTimeline will require update logic in order to change its luminosity and color.

Navigate to the Components tab in the BP_LightActor's Blueprint Editor and select the OverlapCollision box component. From the Details Panel, scroll down to the Events category and click the + icon next to the On Component Begin Overlap event.
Drag off the On Component Begin Overlap(OverlapCollision) node's execution pin and connect it into the PointTimelineComponent node's Play pin.
From the Components tab, select and drag the PointLight component into the Event Graph.
Drag off the PointLight's pin and select Set Intensity from the actions menu search.
From the PointLightTimeline node, drag off the Light Brightness Float Track pin and select float * float from the actions menu search.
From the My Blueprint tab click and drag the BrightnessMultiplier float variable into the Event Graph, select Get Brightness Multiplier, then connect it into the float * float node.
Connect the Update Execution pin to the Set Intensity node, then connect the result from the float * float node to the New Intensity input pin.
Drag off the PointLight node and select Set Light Color from the actions menu search.
From the PointLightTimeline node, drag off the Light Linear Color Track pin and connect it to the New Light Color pin of the Set Light Color node. Then connect the execution pin from the Set Intensity node to the Set Light Color node.
Compile and Save.

Finished Blueprint

Level Setup

To best demonstrate the functionality of the code you have written, you will need to remove all light sources from the level.

Begin by placing an instance of your BP_LightActor into the level.
Navigate to the World Outliner and select the Atmospheric Fog Actor. From the Details Panel navigate to the Sun category, and set its Default Brightness value to 0.
Delete the Sky Sphere Actor from the World Outliner.
Delete the Light Source Actor from the World Outliner as well.
Navigate to the Toolbar, and select Build to re-build the lighting in the level.
Once the lighting has finished building, the level will look similar to the image below.

End Result

Now that the Light Actor and level have been set up, click PIE to automatically take possession of the spectator Pawn.

You can control the spectator Pawn and navigate into the Light Actor's box component bounds.

Once the Timeline Component's Play function has been triggered, the light's color and luminosity should begin to change over a 5-second timespan.

This document describes how to set up a light Actor that changes color and slowly fades away on contact.

This will be done using a Point Light Component containing a Box Component to serve as an overlap trigger and a Timeline component to manipulate the Point Light Actor.

Creating the Fading Light Actor

Begin by creating a New > Games > Blank > C++ project named FadingLights.
From the C++ Class Wizard, create a new Actor class named LightActor.
Navigate to the LightActor.h file and declare the following:
```
#include "Components/TimelineComponent.h"
```

Next, in the LightActor class definition, add the following code:

public:

        UPROPERTY(EditAnywhere)
        UCurveFloat* PointLightFloatCurve;

        UPROPERTY(EditAnywhere)
        UCurveLinearColor* PointLightColorCurve;

protected: 

        //TimelineComponent to animate the point light component.
        UPROPERTY(VisibleAnywhere, BlueprintReadWrite)
        UTimelineComponent* LightTimelineComp;

        //BoxComponent which will be used as our proximity overlap volume.
        UPROPERTY(EditAnywhere, BlueprintReadWrite)
        class UBoxComponent* LightOverlapVolume;

        UPROPERTY(EditAnywhere,BlueprintReadWrite)
        class UPointLightComponent*  PointLightComp;

        //Track used for Pointlight brightness
        FOnTimelineFloat UpdateBrightnessTrack;

        //Track used for Pointlight color
        FOnTimelineLinearColor UpdateColorTrack;

        //Function to Update Light's brightness relative to UpdateBrightnessTrack
        UFUNCTION()
        void UpdateLightBrightness(float BrightnessOutput);

        //Function to Update Light's color relative to UpdateColorTrack
        UFUNCTION()
        void UpdateLightColor(FLinearColor ColorOutput);

        UPROPERTY(EditDefaultsOnly)
        float BrightnessMultiplier;

Navigate to LightActor.cpp and add the following class libraries.

#include "Components/BoxComponent.h"
#include "Components/PointLightComponent.h"

In the constructor for ALightActor::ALightActor declare the following:

//Create our Default Components
PointLightComp = CreateDefaultSubobject<UPointLightComponent>(TEXT("PointLightComp"));
LightTimelineComp = CreateDefaultSubobject<UTimelineComponent>(TEXT("LightTimelineComp"));
LightOverlapVolume = CreateDefaultSubobject<UBoxComponent>(TEXT("LightOverlapVolume"));

//Setup our Attachments
RootComponent = LightOverlapVolume;
PointLightComp->AttachToComponent(LightOverlapVolume,FAttachmentTransformRules::KeepRelativeTransform);

//Initialize Brightness Multiplier
BrightnessMultiplier = 20.0f;

Next, implement the point light component's UFunction methods:

void ALightActor::UpdateLightBrightness(float BrightnessOutput)
{
    PointLightComp->SetLightBrightness(BrightnessOutput * 20.0f);
}

void ALightActor::UpdateLightColor(FLinearColor ColorOutput)
{
    PointLightComp->SetLightColor(ColorOutput);
}

Then, in the BeginPlay method, add the following code:

    //Binding our float and color track to their respective functions
    UpdateBrightnessTrack.BindDynamic(this, &ALightActor::UpdateLightBrightness);
    UpdateColorTrack.BindDynamic(this, &ALightActor::UpdateLightColor);

    //If we have a float curve, bind it's graph to our update function
    if (PointLightFloatCurve)
    {
       LightTimelineComp->AddInterpFloat(PointLightFloatCurve, UpdateBrightnessTrack);
    }

    //If we have a linear color curve, bind it's graph to our update function
     if (PointLightColorCurve)
    {
       LightTimelineComp->AddInterpLinearColor(PointLightColorCurve, UpdateColorTrack);
    }

Compile your code.
From the Content Browser, navigate to the C++ Classes folder.
Right click the LightActor class, select Create Blueprint Class based on LightActor, and name the Blueprint Actor BP_LightActor.

The BP_LightActor's Class Defaults will appear as they do below:

Work-In-Progress Code

LightActor.h

//Copyright 1998-2021 Epic Games, Inc. All Rights Reserved.

#pragma once

#include "CoreMinimal.h"
#include "GameFramework/Actor.h"
#include "Components/TimelineComponent.h"
#include "LightActor.generated.h"

UCLASS()
class FADINGLIGHTS_API ALightActor : public AActor
{

GENERATED_BODY()

public:
    // Sets default values for this actor's properties
    ALightActor();

    UPROPERTY(EditAnywhere)
    UCurveFloat* PointLightFloatCurve;

    UPROPERTY(EditAnywhere)
    UCurveLinearColor* PointLightColorCurve;

protected: 
    // Called when the game starts or when spawned
    virtual void BeginPlay() override;

    //TimelineComponent to animate the point light component.
    UPROPERTY(VisibleAnywhere, BlueprintReadWrite)
    UTimelineComponent* LightTimelineComp;

    //BoxComponent which will be used as our proximity overlap volume.
    UPROPERTY(EditAnywhere, BlueprintReadWrite)
    class UBoxComponent* LightOverlapVolume;

UPROPERTY(EditAnywhere,BlueprintReadWrite)
    class UPointLightComponent*  PointLightComp;

    //Track used for Pointlight brightness
    FOnTimelineFloat UpdateBrightnessTrack;

    //Track used for Pointlight color
    FOnTimelineLinearColor UpdateColorTrack;

    //Function to Update Light's brightness relative to UpdateBrightnessTrack

UFUNCTION()
    void UpdateLightBrightness(float BrightnessOutput);

    //Function to Update Light's color relative to UpdateColorTrack
    UFUNCTION()
    void UpdateLightColor(FLinearColor ColorOutput);

    UPROPERTY(EditDefaultsOnly)
    float BrightnessMultiplier;

    public:
        // Called every frame
        virtual void Tick(float DeltaTime) override;

    }

LightActor.cpp

    //Copyright 1998-2021 Epic Games, Inc. All Rights Reserved.

    #include "LightActor.h"
    #include "Components/PointLightComponent.h"
    #include "Components/BoxComponent.h"

    // Sets default values
    ALightActor::ALightActor()
    {
        // Set this actor to call Tick() every frame.  You can turn this off to improve performance if you don't need it.
        PrimaryActorTick.bCanEverTick = true;

        //Create our Default Components
    PointLightComp = CreateDefaultSubobject<UPointLightComponent>(TEXT("PointLightComp"));
         LightTimelineComp = CreateDefaultSubobject<UTimelineComponent>(TEXT("LightTimelineComp"));
         LightOverlapVolume= CreateDefaultSubobject<UBoxComponent>(TEXT("LightOverlapVolume"));

    //Setup our Attachments
        RootComponent = LightOverlapVolume;
        PointLightComp->AttachToComponent(LightOverlapVolume,FAttachmentTransformRules::KeepRelativeTransform);}

    // Called when the game starts or when spawned
    void ALightActor::BeginPlay()
    {

    //Binding our float and color track to their respective functions
    UpdateBrightnessTrack.BindDynamic(this, &ALightActor::UpdateLightBrightness);
    UpdateColorTrack.BindDynamic(this, &ALightActor::UpdateLightColor);

        //If we have a float curve, bind it's graph to our update function
        if (PointLightFloatCurve)
        {
          LightTimelineComp->AddInterpFloat(PointLightFloatCurve, UpdateBrightnessTrack);
        }
        //If we have a linear color curve, bind it's graph to our update function
    if (PointLightColorCurve)
        {
           LightTimelineComp->AddInterpLinearColor(PointLightColorCurve, UpdateColorTrack);
        }
    }

    void ALightActor::UpdateLightBrightness(float BrightnessOutput)
    {
        PointLightComp->SetLightBrightness(BrightnessOutput * 20.0f);
    }

    void ALightActor::UpdateLightColor(FLinearColor ColorOutput)
    {
        PointLightComp->SetLightColor(ColorOutput);
    }

    // Called every frame
    void ALightActor::Tick(float DeltaTime)
    {
        Super::Tick(DeltaTime);
    }

Creating and Binding the Collision Overlap Event