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

Ray tracing is a lighting technique that brings an extra level of realism to games. It emulates the way light reflects and refracts in the real world, providing a more believable environment than what’s typically seen using the static lighting in more traditional games.

A good graphics card can use ray tracing to enhance immersion, but not all GPUs can handle this technique. Read on to decide if ray tracing is essential to your gaming experience and if it justifies spending hundreds on an upgraded GPU.

Virtual photons

To understand just how ray tracing’s revolutionary lighting system works, we need to step back and understand how games previously rendered light and what needs to be emulated for a photorealistic experience.

Games without ray tracing rely on static “baked in” lighting. Developers place light sources within an environment that emit light evenly across any given view. Moreover, virtual models like NPCs and objects don’t contain any information about any other model, requiring the GPU to calculate light behavior during the rendering process. Surface textures can reflect light to mimic shininess, but only light emitted from a static source.

Overall, the GPU’s evolution has helped this process become more realistic in appearance over the years, but games still aren’t photorealistic in terms of real-world reflections, refractions, and general illumination.  To accomplish this, the GPU needs the ability to trace virtual rays of light.

In the real world, visible light is a small part of the electromagnetic radiation family perceived by the human eye. It contains photons that behave both as a particle and as a wave. Photons have no real size or shape — they can only be created or destroyed.

That said, light could be identified as a stream of photons. The more photons you have, the brighter the perceived light. Reflection occurs when photons bounce off a surface. Refraction occurs when photons — which travel in a straight line — pass through a transparent substance and the line is redirected, or “bent.” Destroyed photons can be perceived as “absorbed.”

Ray tracing in games attempts to emulate the way light works in the real world. It traces the path of simulated light by tracking millions of virtual photons. The brighter the light, the more virtual photons the GPU must calculate, and the more surfaces it will reflect, refract, and scatter off and from.

The process isn’t anything new. CGI has used ray tracing for decades, though the process required farms of computers in the early days to generate a full movie given a single frame could take hours or even days to render. Now home PCs can emulate ray-traced graphics in real time, leveraging hardware acceleration and clever lighting tricks to limit the number of rays to a manageable number.

But here’s the real eye-opener. Like any movie or TV show, scenes in CGI animation are typically “shot” using different angles. For each frame, you can move a camera to capture the action, zoom in, zoom out, or pan an entire area. And like animation, you must manipulate everything on a frame-by-frame basis to emulate movement. Piece all the footage together and you have a flowing story.

In games, you control a single camera that’s always in motion and always changing the viewpoint, especially in fast-paced games. In both CGI and ray-traced games, the GPU not only must calculate how light reflects and refracts in any given scene, but it also must calculate how it’s captured by the lens — your viewpoint. For games, that’s an enormous amount of computational work for a single PC or console.

Unfortunately, we still don’t have consumer-level PCs that can truly render ray-traced graphics at high framerates. Instead, we now have hardware that can cheat effectively.

Let’s get real

Ray tracing’s fundamental similarity to real life makes it an extremely realistic 3D rendering technique, even making blocky games like Minecraft look near photo-realistic in the right conditions. There’s just one problem: It’s extremely hard to simulate. Recreating the way light works in the real world is complicated and resource-intensive, requiring masses of computing power.

That’s why existing ray-tracing options in games, like Nvidia’s RTX-driven ray tracing, aren’t true to life. They’re not true ray tracing, whereby every point of light is simulated. Instead, the GPU “cheats” by using several smart approximations to deliver something close to the same visual effect, but without being quite as taxing on the hardware. This will likely change in future GPU generations, but for now, this is a step in the right direction.

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, static light sources. Placing all these “stage lights” 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 this technique but the implementation isn’t perfect.

Because of that, half-measures like only ray-tracing shadows or reflective surfaces are popular. Other games leverage Nvidia technologies like 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.

Nvidia’s Turing architecture uses 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, all of which have RT cores.

Nvidia released a breakdown of generating a single frame of Metro Exodus, 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 can 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 available. There are also Reshade “path tracing” post-processing effects that 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.

What about AMD?

AMD graphics cards currently don’t offer any kind of ray tracing acceleration, but that doesn’t mean they’re incapable. Crytek released a demo called Neon Noir in 2019, which showed high-level ray tracing effects on a $300 AMD RX Vega 56, running at a smooth 30 FPS. That’s hardly stellar, but it shows that ray tracing is possible. The RX 5700 XT and Radeon VII are much faster than the Vega 56 and can deliver much better frame rates.

When AMD debuts its long-rumored “Big Navi” graphics card later in 2020, it will no doubt be that much better again. But it will also reportedly support hardware-accelerated ray tracing. It’s not clear whether it will work in the same way as Nvidia’s RT cores, or will be designed to offer ray tracing to a wider array of games, but the support will be there.

Hardware-accelerated ray tracing will be available in the Xbox Series X and PlayStation 5 this holiday season. Both systems will use AMD Navi graphics technology, so Big Navi may just be a hint of what will become mainstream ray-tracing GPUs later this year.

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. However, 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 card you can afford. A $1,000+ 2080 Ti isn’t necessary, but an RTX 2060 Super or 2070 is probably the baseline you want to target. 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, though newer games like Control and MechWarrior 5: Mercenaries look great too. 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.

You can test how ready your PC is for ray tracing with UL Benchmark’s Port Royal ray tracing benchmark.

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