Ray-Traced and SSGI Lighting Studies in UE4

Introduction

Hey! 

My name is Aitor Rández, I am a student in my final year at Digital Arts and Entertainment (DAE) in Belgium. I am passionate about environment art and everything that it involves, such as the making of props, level design, and lighting. I am looking for an internship from February to June 2021.

In this article, I will present how I created the lighting for my latest study. The lighting setup can be downloaded and recreated with your own assets or Megascans assets. 

Light Study Rocks: Goal

The goal of the study was to recreate a scene inspired by the trailer of UE5 with the limitations of UE4 and with the help of Megascans assets, in a short amount of time. 

Analyzing Our Weapons

What is available in UE4 and how can those tools be utilized to their full advantage?

The most accurate type of lighting we have now is baked lighting mixed with ray tracing. I decided to use SSGI instead of ray tracing for the global illumination, for performance purposes. This tool calculates the indirect lighting dynamically that is shown on screen  (SSGI is also very expensive).

Before We Start

1. Turn on the ray tracing feature, do not worry if the GPU is not the 20XX series or above. Go to the project settings and search for ‘ray tracing’.
2. Make sure that the engine is running with DirectX 12. In project settings, search for platforms, then Windows, Default RHI, and select DirectX 12.

3. Turn on SSGI: go to project settings and search for SSGI.

Restart the engine and you should be ready to go.

Lights, Lights and More Lights

The sun:

I wanted a very bright sun, a foggy atmosphere, and a high contrast between the shadows and the highlighted areas. Therefore, the color of the light is warm and the shadows are cold, as shown in the reference.

Everyone wants those god rays. Yes, I know you want them too and to achieve that, turn on Cast Volumetric Shadows, add the Exponential Height Fog to the scene and turn on Volumetric Fog.

Exponential Height Fog and Directional Light settings:

The light is on Stationary, meaning that it is a combined Baked and (Dynamic) ray traced lighting. It is a mix of the best qualities from Stationary and Dynamic, the Lightmass (Baked) settings can be changed in the world settings. Remember to adjust the size of the lightmaps for the objects.

I did not use AO on my Lightmass since I used ray tracing.

Epic Games have a cool video where they compared and explained the most important settings for Lightmass. I encourage you to take a look to have a better understanding of Lightmass.

The Skylight:

The skylight is what gives the realism feeling to the scene. The cold shadows are created from the sky color bouncing off the ground. Add Atmospheric Fog to your scene, the brightness of the sky can be boosted with the first option Sun Multiplier. Be careful as it may ruin the scene, but if done correctly, it can give the scene a realistic feeling.

On/Off Atmospheric Fog, you can see the god rays, too:

Atmospheric Fog and Sky Light settings:

Post Processing - Where the Magic Happens

The settings that are more relevant to talk about, in my opinion, are as followed: 

Exposure Settings: The exposure settings are very important. By default, the settings are not that great. It is safer to leave the max and min on the same value as example 1 if you are unsure about the settings. After changing the exposure settings, the dark areas should remain the same, as your screen will not adjust the brightness. The setting that I used can be found in the photo ‘Post Processing Settings’ below. 

Post Process Material: I made a cool material that works like Sharpen from Photoshop. It adds a crisp feeling to the scene, but I suggest to keep it subtle.

To see how the material is made, click here, or download the scene here.

Something that I wanted to achieve for this scene was to create a material that makes the grain appear only on the shadows or very dark spots, similarly to the effect that is achieved by an actual camera at night with a high ISO - dead pixels. Maybe you can give it a try?

Chromatic Aberration and Bloom: A high Chromatic Aberration and Bloom setting can often ruin a good artwork. Always keep in mind that more is not always better.

Ray Tracing: Currently in UE4, Reflections, AO, GI, Translucency, and ray traced lights are available. I used AO, the ray traced lights, and Reflections. The settings can be adjusted according to your hardware. 

By turning on those settings, normally it should work out-of-the-box. The settings can be  switched on and off with the console by using the following commands:

r.RayTracing 0

r.RayTracing 1

Refer to other helpful commands here.

Post Processing Settings:

Recap 

Direct Light, Sky Light, Exponential Height Fog, Atmospheric Fog, and a Post Processing Volume are added. Ray Tracing and Screen Space Global Illumination are turned on. 

For reference, click here to download a project with the same lighting setup and material for sharpening.

Aitor Rández, 3D Artist