What Is Ray Tracing? | Digital Tendencies

Ray tracing is a lighting technique that gives games an extra level of realism. It emulates the way light is reflected and refracted in the real world, and provides a more believable environment than is usually the case with conventional games with static lighting.

A good graphics card can use ray tracing to improve 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 is justified to spend hundreds on an updated GPU.

Virtual photons

To understand how Ray Tracing's revolutionary lighting system works, we need to step back and understand how games have previously rendered light and what a photo-realistic experience needs to be emulated.

Games without ray tracing are based on static "burned-in" lighting. Developers place light sources in an environment that emits light evenly across a particular view. In addition, virtual models such as NPCs and objects do not contain information about other models, so the GPU has to calculate the light behavior during the rendering process. Surface textures can reflect light to imitate gloss, but only light emitted from a static source.

Overall, the development of the GPU has helped make this process more realistic over the years, but games are still not photo-realistic in terms of real reflections, refractions, and general lighting. To achieve this, the GPU needs the ability to track virtual light rays.

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

That is, 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 – moving 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 tries to emulate how light works in the real world. It tracks the path of simulated light by tracking millions of virtual photons. The brighter the light, the more virtual photons the GPU has to calculate and the more surfaces are reflected, refracted and scattered.

The process is nothing new. CGI has been using ray tracing for decades, although the process initially required computer farms to create a full movie because rendering a single frame can take hours or even days. Now home PCs can emulate raytrace graphics in real time, using hardware acceleration and clever lighting tricks to limit the number of rays to a manageable number.

But here's the real eye opener. As in any film or television program, scenes in CGI animations are usually “captured” from different angles. For each image, you can move a camera to capture, zoom in, zoom out, or pan an entire area. And like with animations, you have to edit everything frame by frame to emulate motion. Put all the footage together and you have a flowing story.

In games, you control a single camera that is always on the move and always changes your perspective, especially in fast games. In both CGI and Raytrace games, the GPU not only has to calculate how light is reflected and refracted in a particular scene, but also how it is captured by the lens – your point of view. For games, this means a huge amount of computing for a single PC or console.

Unfortunately, we still don't have consumer-level PCs that can really render raytrace graphics at high frame rates. Instead, we now have hardware that can effectively cheat.

Let’s be real

The fundamental similarity of ray tracing to real life makes it an extremely realistic 3D rendering technique that even block games like Minecraft appear almost photo-realistic under the right conditions. There is only one problem: it is extremely difficult to simulate. Restoring how light works in the real world is complicated and resource intensive, and requires a lot of computing power.

For this reason, existing ray tracing options in games such as Nvidia's RTX-controlled ray tracing are not true to life. They are not real ray tracing, where every point of light is simulated. Instead, the GPU "cheats" by using multiple smart approximations to achieve a similar visual effect, but without stressing the hardware. This is likely to change in future generations of GPUs, but at the moment this is a step in the right direction.

Most ray tracing games today use a combination of traditional lighting techniques, commonly referred to as rasterization, and ray tracing on certain surfaces, such as reflective puddles and metalwork. Battlefield V is a good example of this. You see the reflection of troops in the water, the reflection of terrain in airplanes and the reflection of explosions on the paintwork of a car. It is possible to display 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 for shadows to make them more dynamic and realistic. You will see that this was very effective in Shadow of the Tomb Raider.

Raytrace lighting can create much more realistic shadows in dark and light scenes, with softer edges and better resolution. It is extremely difficult to achieve this look without ray tracing. Developers can only fake it through careful, controlled use of preset static light sources. Placing all of these “stage lights” takes a lot of time and effort – and even then the result is not quite right.

Some games are a hit and use ray tracing for global lighting to effectively track an entire scene. However, this is the most computationally intensive and requires the most powerful modern graphics card to function effectively. Metro Exodus uses this technique, but the implementation is not perfect.

For this reason, half measures such as raytracing shadows or reflective surfaces are popular. Other games use Nvidia technologies such as denoising and deep learning super sampling to improve performance and cover up some of the visual problems caused by rendering fewer rays than would be required to create a truly ray-traced scene. These are still reserved for pre-rendered screenshots and films, on which powerful servers can spend days rendering individual frames.

The hardware behind the rays

To cope with these relatively modest implementations of ray tracing, the RTX graphics card generation from Nvidia introduced hardware, which was specially developed for ray tracing.

Nvidia's Turing architecture uses new RT cores to handle the technology in real time. They are not strictly necessary for the ray tracing function, since ray tracing effects can be carried out on graphics cards of the GTX 10 and 16 series, although they are far less powerful than first-class RTX cards like the 2070, 2080 and 2080 Ti that all RT cores have.

Nvidia released a breakdown of Metro Exodus single frame generation, showing how the rendering pipeline is structured and how it is affected by ray tracing. While an RTX 2080 and a GTX 1080 Ti are roughly comparable in performance for games without ray tracing, when applying ray tracing to a scene it can take much longer for the 1080 Ti to produce the same picture without the dedicated RT cores.

For this reason, even the most powerful GTX graphics cards like the 1080 Ti have problems with raytrace games from 1080p. But RT cores are not a silver bullet. Even the 2080 Ti, the world's most powerful consumer graphics card with the most RT cores, has problems achieving 60 fps or more at 1440p in games like Battlefield V or Metro Exodus with activated ray tracing function. This is a card that can deliver high frame rates at 4K without the ray tracing feature enabled.

But it doesn't have to be that way. Nvidia's ray tracing method isn't the only option available. There are also reshade post-processing effects for path tracking that provide comparable graphics without the same drop in performance.

You still want a powerful graphics card for ray tracing regardless of implementation. However, with technology gaining ground among game developers, we may see a wider range of supporting hardware at much cheaper prices.

What about AMD?

AMD graphics cards do not currently offer ray tracing acceleration, but this does not mean that they are unable. Crytek released a demo called Neon Noir in 2019 that showed high-grade ray tracing effects on a $ 300 AMD RX Vega 56 at a speed of 30 FPS. This is hardly outstanding, 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.

If AMD launches its long rumored "Big Navi" graphics card later in 2020, it will undoubtedly be so much better again. It is also said to support hardware accelerated ray tracing. It's not clear if it works the same as Nvidia's RT cores or how ray tracing is offered for a larger number of games, but the support will be there.

Hardware accelerated ray tracing will be available for Xbox Series X and PlayStation 5 this Christmas. Both systems will use AMD Navi graphics technology, so Big Navi may just be an indication of what will become popular ray tracing GPUs later this year.

How can you see ray tracing at home?

The first point of contact is the purchase of an Nvidia graphics card, as this is currently required for publicly available Raytrace games. Any RTX or GTX card is suitable if you just want to see what a raytrace scene looks like. However, if you want to play with a resolution above 1080p and with frame rates of approximately or over 60 FPS, the most powerful and therefore most expensive graphics card you can afford is the best choice. A $ 1,000 + 2080 Ti is not required, but an RTX 2060 Super or 2070 is probably the baseline you want to target. That means spending between $ 350 and $ 550.

As far as games go, the selection is still quite limited. The most comprehensive implementations of ray tracing can still be found in the earliest RTX demo games like Battlefield V, Shadow of the Tomb Raider and Metro Exodus, although newer games like Control and MechWarrior 5: Mercenaries also look great. Stay in the Light is a new indie horror game based solely on the use of raytrace reflections and shadows. You can now play through a revised Quake II with RTX ray tracing.

With the Port Royal Ray Tracing Benchmark from UL Benchmark you can test how ready your PC is for ray tracing.

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