What Is Ray Tracing? | Digital Trends

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. But what is ray tracing, exactly? And more importantly, how does it work?

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 s 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 . Take the comparison of reflections in GTA V below as an example.

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.

Ray tracing alone makes a huge difference in Minecraft. Matthew Smith / Digital Trends

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 re-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 a