Working with Lumen & Nanite in Unreal Engine 5

Introduction

My name is Michael Gerard and I am a Landscape Artist. I am working on the Unreal Engine since 2015. Since our last conversation, I have done some freelance work in various fields such as video games and virtual production.

Unreal Engine 5

To be honest, I didn't expect UE5 to be released in early access just before the summer and I didn't expect much when it launched because early accesses are rarely full of content and often frustrating. But from the very first launch, whether it is about the creation of the project or the new interface, it's already a small revolution.

It's so much cleaner than on UE4 and the fact that you can retract the menus greatly improves the way you work.

The most exciting thing for me was Lumen, I really wanted to see what it looked like in reality, beyond the demonstration videos. The result was amazing, the color support, the emissive materials that emit light, and the volumetric fog that recovers all this information, it's incredible.

Then I tried Nanite out of curiosity, and when I saw how easy it was to manage millions of polygons converted into cells, I decided that I really had to make a scene in UE5.

The Cave Project

It's a really small scene, there is nothing else than what is visible on the screenshots and you can see that it's not placed with much precision, the goal was to create a cave.

The other goal of this scene was to see how far the Nanite/Lumen combination can go in this early access and what are the current limits of these two technologies.

Nanite

The classical way of mesh optimization is to create LODs. To put it simply, it is the same mesh the density of which is reduced at each new level (starting from level 0) to reduce the impact on resources. Based on the distance between the object and the camera, the engine will display the LOD0/1/2/3.

This technique is very good but limited because it is necessary to find the right ratio between the number of polygons and desired quality.

Nanite thinks differently, here it is no longer a question of basing itself on LODs but on clusters.

Nanite would fragment the object into several clusters whose size varies according to the distance. The closer the camera is, the smaller the clusters will be, the further away the camera is, the larger the clusters will be.

Thanks to this technology it is possible to import very detailed meshes (several million polygons) and to reduce their size by simply converting any mesh into Nanite mesh.

To convert a mesh into a Nanite mesh, it is quite simple since you just have to right-click on the mesh, go to the first line "Nanite" and select "Enable".

But beware! There are some prerequisites for Nanite to work. The material associated with your mesh must be "opaque" and without World Position Offset. Nanite does not yet support transparent/masked materials.

In my tests, I tried to convert an entire tree to Nanite, but there is a similar problem with using meshes that require an opacity mask or transparency, overdraw. Extreme overdrawing of multiple meshes can impact performance.

I doubt the need to use Nanite on small objects. I have used it on my mushrooms, but they go to a lower density quite quickly. Using LODs is sufficient for these kinds of objects in my opinion.

Lumen

Lumen is what we call a "global illumination", the goal of this technology is to make the light bounce on various surfaces to send back a light called "indirect light". It is this indirect light that will recover the information of colors and will send them back.

The global illumination is already present in UE4, but it can be tricky in some cases and sometimes requires the addition of point light to brighten the darkest areas. This is less the case in UE5 with Lumen.

In my scene the light is quite simple, I increased the intensity values for a more powerful light, indirect light to have more important bounces and I also increased the Volumetric Light value to create bigger god-rays 

In my opinion, the real strength of Lumen is that it is not necessary to adjust several parameters to get a very good result. It's really easy to use and quick to set up.

I didn't encounter any major problems, except for the instances not being supported. This forced me to place a lot of things manually. But I think it's clearly an early access bug and it will be fixed in the release or in updates if they decide to do it, so I'm not worried.

Impressions

UE5 is really promising and although it is only in early access, what it allows you to do is great. Yes, it suffers from instability and fluidity problems, but that doesn't prevent you from discovering Lumen or Nanite or from getting used to the new interface. Personally, I like Lumen a lot, I think it shows, I find this new feature really impressive, and knowing that it will probably be improved through various future updates tells me that it has not finished impressing me.

Being an early access version, it's hard to make a solid list of things to improve. The most common problems are certainly known by the developers and there are still so many things to see that I prefer to follow the flow of updates and see how it all evolves. But I am quite confident, they have shown throughout the existence of UE4 (which is far from over with the planned 4.27) that they know how to improve their engine in the right direction. I can't wait to see what UE5 will become in the next few years. UE4 is currently a reference, UE5 may become a legend, who knows.

Michael Gerard, Landscape Artist

Interview conducted by Arti Sergeev