ray tracing, to games an extra realism a level that brings is a lighting technique. By mimicking the way light reflects and refracts in the real world, it provides a more believable environment than those seen using static lighting in more traditional games. So what exactly is ray tracing? And more importantly, how does it work? A good graphics card can use ray tracing to increase immersion, but not all GPUs can handle this technique. Read on to decide whether ray tracing is essential to your gaming experience and whether it justifies spending hundreds of dollars on an upgraded GPU.
Ray Tracing – Virtual Photons
To understand how ray tracing's revolutionary lighting system works, we need to take a step back and understand how games have previously rendered light and what needs to be emulated for a photorealistic experience. Non-ray tracing games rely on static “baked” lighting. Developers place light sources in an environment that emits light evenly in any view. Moreover, virtual models such as NPCs and objects do not contain information about any other model and require the GPU to calculate the lighting behavior during rendering. Surface textures can reflect light to mimic gloss, but can only reflect light emitted from a static source. Take the comparison of reflections in GTA V below as an example.
Overall, the evolution of the GPU has helped this process look more realistic over the years, but games are still not photorealistic in terms of real-world reflections, refractions, and overall lighting. To achieve this, the GPU must be able to follow virtual light rays.
In the real world, visible light is a small part of the family of electromagnetic radiation perceived by the human eye. It contains photons that behave both as particles and as waves. Photons have no real size or shape – they can only be created or destroyed.
However, light can be described 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 traveling in a straight line pass through a transparent material and the line is redirected or “bent.” The destroyed photons can be detected as “absorbed”.
Ray tracing in games attempts to mimic 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 the light reflects, refracts, and scatters.
This process is nothing new. CGI has been using ray tracing for decades, but in the early days it required farms of computers to render a full movie, as rendering a single frame could take hours or even days. Home computers can now emulate ray-traced graphics in real time, leveraging hardware acceleration and clever lighting tricks to limit the number of rays to a manageable number.
Here's a real eye-opener: As with any movie or TV show, scenes in CGI animation are often “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 have to manipulate everything frame by frame to mimic movement. When you put all the images together, you have a flowing story.
In games, especially fast-paced ones, you control a single camera that is always moving and constantly changing its perspective. In both CGI and ray-traced games, the GPU must not only calculate how light is reflected and refracted in any given scene, but also how it is captured by the lens – depending on your perspective. For games, this is an enormous amount of computational work for a single computer or console.
Unfortunately, we still don't have consumer-level computers that can truly handle ray-traced graphics at high frame rates. Instead, we now have hardware that can effectively cheat.
Ray Tracing – Realistic Graphics
Ray tracing's fundamental similarity to real life makes it an extremely realistic 3D rendering technique, even making blocky games like Minecraft look almost photorealistic in the right conditions. There's just one problem: It's extremely difficult to simulate. Recreating the way light works in the real world is complex and resource-intensive, requiring large amounts of computing power.
Therefore, current ray tracing options in games, such as Nvidia's RTX-focused ray tracing, are not realistic. These are not true ray tracing, where every point of light is simulated. Instead, the GPU “cheats” by using a variety of clever approaches to deliver something close to the same visual effect, but without taxing the hardware as much.
Most ray tracing games now use a combination of traditional lighting techniques, often called rasterization, and ray tracing techniques on certain surfaces, such as reflective puddles and metalwork. Battlefield V is a great example of this. You see the reflection of soldiers in the water, the reflection of the terrain on planes, and the reflection of explosions on the paintwork of a car. 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 used to make shadows appear more dynamic and realistic. You'll see this used to great effect in Shadow of the Tomb Raider.
Ray-traced lighting can create much more realistic shadows in dark and light scenes, providing softer edges and greater definition. Achieving this look without ray tracing is extraordinarily difficult. Developers can only emulate this by using preset, static light sources in a careful and controlled manner. It takes a lot of time and effort to place all these “footlights” – and even then the result is not quite right.
Some games use ray tracing for global illumination, effectively ray tracing the entire scene. However, this is the most computationally expensive option and requires the most powerful modern graphics cards to run effectively. Metro Exodus uses this technique, but the implementation isn't perfect.
That's why only half-measures like ray tracing shadows or reflective surfaces are popular. Other games take advantage of Nvidia technologies like denoising and Deep Learning Super Sampling to improve performance and cover up some of the visual hiccups that come from processing fewer rays than are necessary to render a true ray tracing scene. These technologies are still reserved for pre-rendered screenshots and movies, where high-powered servers can spend days processing a single frame.
How Do Rays Work?
Nvidia's RTX 20 series graphics cards offered hardware built specifically for ray tracing to handle even these relatively modest applications of ray tracing.
All RTX cards now support ray tracing, and there's another way to cheat performance on the latest RTX 40 series GPUs. SER, or Shader Execution Reordering, is available on the RTX 4090 and RTX 4080, and Nvidia says it can improve performance in ray-traced games by 25%. It works by reordering ray tracing instructions when they are processed by the GPU, optimizing the task for the available computing power.
While the early days of ray tracing were rough, Nvidia's latest cards have performed much better. With the new generation SER and DLSS 3, we can see ray tracing that does not reduce your frame rate. Nvidia's new DLSS 3.5 also promises to support ray tracing with Ray Reconstruction.
Nvidia's ray tracing method isn't the only option available, though. There are also Reshade “path tracing” post-processing effects that offer similar visuals, although they do not have the same performance.
AMD now has options for ray tracing as well, more on that later.
You'll still need a powerful graphics card for ray tracing no matter the application, but as the technique becomes more widespread among game developers, we could see a wider range of supporting hardware at much more affordable prices.
While ray tracing has been mostly focused on PCs, it's starting to make its way into other devices as well. Apple recently announced that the iPhone 15's A17 Bionic chip features hardware-accelerated ray tracing, including in games.
How to see ray tracing at home
To see ray tracing at home, you'll need a new, expensive graphics card. Hardware-accelerated ray tracing is only available on Nvidia RTX GPUs or AMD's RX 6000 series GPUs. GTX 10 series and 16 series cards support ray tracing but lack the RT cores that would make it comfortably playable.
If you're looking to game at resolutions above 1080p and frame rates of 60fps or higher, your best bet is to splurge on a top-end graphics card. At 4K, the RTX 3080 and RX 6800 XT are the standout cards, but you can also get by with the RTX 1440 or RX 3070 if you're willing to step up to 6800p in certain games.
Although there are a limited number of games with ray tracing features, this number is gradually increasing. The best examples of ray tracing include early RTX demos like Battlefield V, Shadow of the Tomb Raider, and Metro Exodus. Newer games like Control and MechWarrior 5: Mercenaries also look interesting. Stay in the Light is an indie horror game created using ray-traced shadows and reflections. Quake II, remastered with RTX ray tracing, is another great example.
There are fewer ray tracing games on the market, but the industry is growing. As the PlayStation 5 and Xbox Series X begin touting ray tracing, competitors will soon follow suit. The multiplatform game Watch Dogs 2 differs from the new Watch Dogs: Legion in that the new game introduces ray tracing to run on consoles and computers.
Try using UL Benchmark's Port Royal ray tracing to determine if your computer will work with ray tracing.
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