What is ray tracing, and how will it change games?

Nvidia’s RTX 2000 graphics cards introduced ray tracing to the world of gaming in the latter-half of 2019, but today there are a variety of RTX and GTX cards that support it. The fancy-new lighting technique is a serious resource hog, meaning that the more expensive and modern cards handle it best, but most Nvidia graphics cards from the past few years can take a crack at its real time reflections and shadow effects.

But, what is ray tracing? And is it really worth upgrading for?

Virtual photons

Graphics technology is usually hard to explain, but ray tracing is rather simple. It attempts to emulate the way light works in the real world. Instead of creating pre-designed, or “baked-in” lighting for scenes in games, ray tracing traces the path of simulated light. Or, rather, millions of simulated lights. The light bounces off objects as it moves and interacts with their properties. If it bounces from a glossy green surface, for instance, its hue may change.

That’s essentially how light works in real life. A particle of light bursts forth from its point of origin and travels along until it interacts with an object, at which point its path is determined by that object’s properties. It might be absorbed by a dense, dark object, or almost entirely reflected by a mirror.

Ray tracing’s fundamental similarity to real life makes it an extremely realistic 3D rendering technique. There’s just one problem: It’s hard to simulate. Recreating the way light actually works in the world is complicated and resource intensive, requiring masses of computing power. Even Nvidia’s ray tracing rendering isn’t true ray tracing, whereby every point of light is simulated. Instead, it uses a number of smart approximations to deliver something that’s close to the same visual effect, but without being quite as taxing on the hardware.

Most ray tracing games now use a combination of traditional lighting techniques, typically called rasterization, and ray tracing on specific surfaces such as reflective puddles and metalwork. Battlefield V is a great example of that. You see the reflection of troops in water, the reflection of terrain on airplanes, and the reflection of explosions across a car’s paint. It’s possible to show reflections in modern 3D engines, but not at the level of detail shown in games like Battlefield V when ray tracing is enabled.

Ray tracing can also be leveraged for shadows to make them more dynamic and realistic looking. You’ll see that used to great effect in Shadow of the Tomb Raider.

Ray traced lighting can create much more realistic shadows in dark and bright scenes, with softer edges and greater definition. Achieving that look without ray tracing is extraordinarily hard. Developers can only “fake” it through careful, controlled use of preset light sources. That takes a lot of time and effort and even then, the result isn’t quite right.

Some games go the whole hog and use ray tracing for global illumination, effectively ray tracing an entire scene. But that’s the most computationally expensive and needs the most powerful of modern graphics cards to run effectively. Metro Exodus uses it currently, but its implementation isn’t perfect.

Simulating any of these effects isn’t easy, which is why modern real-time 3D graphics – including those used in 3D games – have to use half measures more often than not. Nvidia uses techniques including denoising and Deep Learning Super Sampling to improve performance and to cover up some of the visual hiccups that occur from rendering fewer rays than would be necessary to create a truly ray-traced scene. Those are still reserved for pre-rendered screenshots and movies where high-powered servers can spend days rendering single frames.

The hardware behind the rays

To handle even these relatively modest implementations of ray tracing, Nvidia’s RTX generation of graphics cards introduced hardware specifically built for ray tracing. The Turing architecture uses the company’s new RT Cores to handle the technique in real time. They aren’t strictly necessary for ray tracing, as ray tracing effects can be run on GTX 10-series and 16-series graphics cards, though they are far less capable than top-tier RTX cards like the 2070, 2080, and 2080 Ti.

Nvidia released a breakdown of generating a single frame of Metro Exodus in April, where it showed how the rendering pipeline is laid out and how it is affected by ray tracing. While an RTX 2080 and GTX 1080 Ti might be roughly comparable in performance for non-ray traced games, when ray tracing is applied to a scene, it can take much longer for the 1080 Ti, without the dedicated RT cores, to generate the same image.

That’s why even the most powerful of GTX graphics cards like the 1080 Ti really struggle with ray traced games at anything above 1080p. But RT cores aren’t a silver bullet. Even the 2080 Ti, the world’s most powerful consumer graphics card with the most RT cores, struggles to hit 60 FPS or more in games like Battlefield V or Metro Exodus with ray tracing enabled at 1440p. This is a card that without ray tracing enabled is able to deliver high frame rates at 4K.

But it doesn’t have to be this way. Nvidia’s ray tracing method isn’t the only option out there. Crytek released a demo called Neon Noir in early 2019, which showed high-level ray tracing effects on a $300 AMD RX Vega 56, running at a smooth 30 FPS. There are also Reshade “path tracing” post-processing effects which deliver comparable visuals without anything like the same performance hit.

You’ll still want a powerful graphics card for ray tracing no matter the implementation, but as the technique catches on with game developers, we may see a broader array of supporting hardware at much more affordable prices.

How can you see ray tracing at home?

The first port of call is getting an Nvidia graphics card, because at this time, publicly available ray traced games require it. Any RTX or GTX card will do if you just want to see what a ray traced scene looks like, but if you want to play at a resolution above 1080p and with frame rates approaching or exceeding 60 FPS, your best bet is with the most powerful and therefore the most expensive graphics cards. A $1,000+ 2080 Ti isn’t necessary, but an RTX 2060 or 2070 is probably the baseline you want to aim for. That means spending between $350 and $550.

As for the games, the selection is still quite limited. The most fully featured implementations of ray tracing can still be found in the earliest of RTX demo games, like Battlefield V, Shadow of the Tomb Raider, and Metro Exodus. But the list is growing all the time. Stay in the Light is a new indie horror game built entirely around the use of ray traced reflections and shadows, and you can play through a remastered Quake II with RTX ray tracing now too.

Other RTX ray traced games planned for 2019 include Remedy Entertainment’s Control, as well as Mundfish’ Atomic Heart, among others.

You can also get a glimpse of high-end ray tracing effects in UL Benchmark’s Port Royal ray tracing benchmark