Skip to main content

How Unreal Engine 5 is tackling the biggest problem in PC gaming

During its State of Unreal address at GDC 2023, Epic announced a wide-ranging suite of features for Unreal Engine 5.2. But perhaps the most important feature coming in the updated engine doesn’t relate to lighting, geometry detail, or ray tracing. It’s all about performance.

Unreal Engine games, rightly or wrongly, have been associated with stuttering and hitches over the past few years. With the new release, Epic is finally tackling the problem head-on, so I thought it was high time to break down why Unreal games so commonly show stutter, what Epic is doing to solve the problem, and when we can expect to see those efforts show up in new releases.

Remember the stutter

Frame time in Gotham Knights on PC.
These frame time spikes manifest as severe stutters in Gotham Knights.

Over the past few years, Unreal Engine has become synonymous with stuttering. We’ve seen it over and over again, from Star Wars Jedi: Fallen Order to Stray to Gotham Knights, and they all have the same issue in common. It’s compilation stuttering.

You’ll typically hear about shader compilation stuttering, but recent sources of hitches aren’t due to individual shaders. In recent graphics APIs like Vulkan and DirectX 12, packages known as Pipeline State Objects (PSOs) are leveraged to tell the game about the state of your GPU. PSOs are meant to make rendering more efficient, allowing dozens of parameters, including shaders, to be interfaced between the API and the GPU in a single package.

However, they introduce a different problem. Because PSOs contain so much information, generating a new one on the fly takes a long time (according to Unreal’s documentation, 100 or more milliseconds). This runtime PSO creation is the source of a stutter, where the engine has to generate a new PSO while you’re actually playing.

To combat this, PSO caching is available in Unreal Engine. This creates a cache of possible PSOs so new ones don’t need to be generated while you’re playing the game, but they aren’t perfect. As Epic explains, PSO precaching can “be burdensome for large projects, and still leave gaps in the cache leading to hitches.” That’s why, even in games that precompile shaders on the GPU, you’ll still occasionally see a stutter (even if they’re few and far between).

Epic is attempting to automate this process by gathering PSOs rather than leaving it to developers to account for every possible GPU parameter. It’s on Epic’s public road map, but only an experimental version is available now. In Unreal Engine 5.2, the goal is to improve PSO caching to further reduce hitches.

All for Fortnite

A scene of Fortnite running in Unreal Engine 5.

There’s a lot to be excited about in Unreal Engine 5 (I’ll get to some of that next), but we don’t have a clear view into how the engine works just yet. So far, it’s only been used in tech demos and Fortnite among major releases. Even games like Redfall that promised to leverage Unreal Engine 5 have backpedaled to Unreal Engine 4.

To be clear, the tools available in Unreal Engine 4 allow developers to optimize their games to avoid stuttering. Atomic Heart is one of many examples of that. But the complex state of PSOs has left the door open to hitches during gameplay, and Epic’s automated PSO gathering was only introduced in Unreal Engine 5.1.

Although I’m happy to see Epic addressing the issue directly, we haven’t seen the automatic PSO cache in process yet. As more complicated, varied releases come out from smaller teams, the demand for PSO generation goes up, and the possibility of hitches and stutters becomes more present.

This is particularly concerning for games that include ray tracing, as Unreal Engine 5 doesn’t support PSO caching for ray tracing PSOs. As Nvidia explains, it’s possible to distribute the work of creating a ray tracing PSO to multiple threads, but that doesn’t necessarily mean developers will use this process.

Still a lot to be excited about

Lighting in Unreal Engine 5.

We still need to see automated PSO gathering in Unreal Engine 5, but there’s actually a ton to be excited about in the engine. First and foremost, Lumen. Lighting is extremely important for graphical fidelity, and expensive techniques like path-traced lighting showcased in Portal RTX are tough on hardware. Lumen splits the difference.

Lumen leverages ray tracing, but it’s a highly optimized form of ray tracing. Instead of painstakingly calculating infinite bounces on detailed objects, Lumen uses abstractions to calculate lighting for most of the scene, only defaulting to detailed lighting closest to the camera. This optimization allows Lumen to run with software ray tracing, ditching the need to have dedicated ray tracing accelerators on your graphics card.

The results are already clear. Fortnite is running on consoles with Lumen at 60 frames per second (fps), and it looks stunning on PC, even in Fortnite’s cartoon world.

A Nanite showcase in Unreal Engine 5.

Nanite works in tandem with Lumen. It’s a virtualized geometry system that contains highly detailed, highly compressed meshes that can adjust during gameplay. It’s basically a complex Level of Detail (LOD) for meshes that automatically swaps between detailed and vague meshes depending on where the camera is looking.

More importantly, Nanite runs on its own rendering pass, so it’s not caught up in the traditional GPU pipeline. That means that your gameplay remains smooth even when Nanite is swapping out mesh complexity. Between Nanite and Lumen, you have two visually impressive, computationally efficient features that raise the bar for graphical fidelity.

Epic shared more during its State of Unreal address, though. Substrate is a new material system in Unreal 5.2 that includes more detailed shader control. Epic demoed this with an opal surface material, showcasing multiple layers and accurate light refraction throughout them.

An opal material in Unreal Engine 5.

The new Procedural Content Generation Framework (PCG) is also exciting, even if it doesn’t directly relate to visual fidelity. With limited input, the PCG can generate new objects to allow developers to rapidly build out worlds with a high level of detail. That’s exciting for more expansive worlds that don’t need the touch of an artist at every corner.

There’s a ton more, from advancements in MetaHuman to full path tracing within Unreal Engine. It’s exciting, but the stuttering issues commonly associated with Unreal Engine releases remain. Hopefully, Epic’s advancements in PSO caching can bypass that issue, but we don’t have a lot of Unreal Engine 5 games to see how that system works yet.

This article is part of ReSpec – an ongoing biweekly column that includes discussions, advice, and in-depth reporting on the tech behind PC gaming.

Editors' Recommendations

Jacob Roach
Senior Staff Writer, Computing
Jacob Roach is a writer covering computing and gaming at Digital Trends. After realizing Crysis wouldn't run on a laptop, he…
Here’s how Intel doubled Arc GPUs’ performance with a simple driver update
intel arc alchemist driver update doubled performance a770 logo respec featured

As newcomers in the world of discrete graphics cards, the best hope for Intel's Arc A770 and A750 was that they wouldn't be terrible. And Intel mostly delivered in raw power, but the two budget-focused GPUs have been lagging in the software department. Over the course of the last few months, Intel has corrected course.

Through a series of driver updates, Intel has delivered close to double the performance in DirectX 9 titles compared to launch, as well as steep upgrades in certain DirectX 11 and DirectX 12 games. I caught up with Intel's Tom Petersen and Omar Faiz to find out how Intel was able to rearchitect its drivers, and more importantly, how it's continuing to drive software revisions in the future.
The driver of your games

Read more
AI is coming for your PC games, but you should be excited, not worried
how ai can change destory pc gaming games respec featured

The tech community has been oversaturated with AI this past week, from ChatGPT to Google Bard, but not without reason. We see fads like NFTs and web3 come and go, but AI is here to stay -- even in your PC games.

It's not all doom and gloom, though. AI and machine learning has already proven itself wildly useful in PC gaming, and it has far-reaching implications for how games are made and experienced. I'm not trying to fit a square peg into a round hole here -- and if you stick with me, you'll see why.
How it's being used now

Read more
I built a couch gaming PC that puts the PS5 to shame — and you can too
A PC sitting next to a PS5 on a coffee table.

The PlayStation 5 is back in stock, and if you've been eagerly waiting to jump into the next generation of gaming, now seems like the time to strike. I'm here to sway you away from a console, though, because you can build a PC for around the same price that puts the PS5 to shame.

PC building is getting more expensive, but prices on the best graphics cards are dropping. With some clever shopping and bit of elbow grease, a gaming PC can deliver better performance and higher-quality visuals without costing much more than Sony's console. Here's the build you need.
Meet the PS5 killer

Read more