What is Ray Tracing?

To understand this new technology, it helps to take a brief look at those that have preceded it. Modern video games have long used a technique called 'rasterization' to render the image on your screen. The way it works is that your PC looks at a 3D scene and calculates the distance to certain objects, where the light is coming from, and which objects are in front of each other. Using that information, it determines what color each pixel should be on your monitor, drawing the scene point by point as a 2D image.

Over time, developers have improved this technology quite a bit, giving objects the ability to cast basic shadows based on light sources, or using tricks like ambient occlusion to add additional shadows independent of light sources. But most games don't actually simulate the way light behaves in the real world, but rather fake it with one technique or another, making it difficult to generate realistic shadows and reflections. (This is why you rarely see mirrors in video games, and when you do, the images inside them are generally very crude.)

Ray tracing is a rendering technique that is intended to simulate the way light bounces off objects, in turn creating more realistic shadows, reflections, and lighting effects. In an interview with Gamers Nexus, NVIDIA's Tom Peterson described it as "a physically based way of creating images, as opposed to an artistic way of creating images."

In the real world, a light source—for example, the lamp in your bedroom—produces photons that bounce around the room until they hit your eye. Ray tracing performs this process in reverse, tracking individual "camera" rays in the scene and tracking how each ray intersects different objects, casts shadows and reflections, and makes its way back to the light source. . This ensures that the computer doesn't waste processing power on objects the camera doesn't see, while still producing much more realistic lighting effects.

This technique has been around for several years, and you've seen it countless times in movies with CGI special effects. Hollywood uses 'render farms' to compute ray tracing for scenes as they are working with massive data sets and generate large numbers of rays for their scenes. It can take hours or days to render even a short scene in a CGI movie that uses ray tracing. In the past, the amount of computation required made it impossible to do in video games, as it must be done in real time so as not to affect the gameplay experience.

So what's so special about RTX cards?

Ray tracing may be common in Hollywood blockbusters, but those effects are created on very expensive render farms, and it can still take hours or even days to render a single frame due to the complexity of the frame. Video games, on the other hand, have to be rendered on your home PC, in real time, hoping to get 60 frames per second. That means advanced lighting techniques like this are not easy to implement.

Nvidia's new family of GeForce RTX GPUs are the first consumer-oriented, gaming-focused graphics cards to include real-time ray tracing... with a few nuances. These cards make use of what NVIDIA calls a "hybrid rendering model" that combines ray tracing with rasterization techniques, thanks to dedicated RT cores designed to compute the intersection of each ray. It also uses special denoising algorithms and dedicated artificial intelligence hardware, called "Tensor Cores' ', to reduce the number of lightning bolts that need to be traced. In other words: they're still 'cheating' a bit, as these cards won't necessarily track entire scenes in real time, but the results are a significant step forward.

How does ray tracing affect gaming performance?

So ray tracing looks amazing, but should you instantly convert and pre-order an RTX card now? Well, don't get too excited yet. NVIDIA ensures significant performance improvements for normal games, especially in 4K. But when it comes to games that use ray tracing, we'll have to wait and see. We played an in-progress build of Shadow of the Tomb Raider and Battlefield 5 on a Geforce RTX 2080 Ti and couldn't hit a constant 60 frames per second at 1920x1080, but an average of 30-50 frames per second.

The Tomb Raider developers claim that the game should be more polished before release, but it wouldn't be crazy to expect some slowdowns when ray tracing is enabled. Another article recently came out saying that Battlefield 5 with ray tracing runs at less than 30fps at 4K resolution, but that Dice still has a lot of optimizations to do before the game is released.

Bottom line: We simply don't know what kind of performance ray tracing will deliver, or at what resolutions it will render games unplayable. It seems likely that players, at least for now, will have to choose between ray tracing at lower resolutions, ray tracing at higher resolutions and lower framerate, or turning ray tracing off entirely.

In general, these cards are the first generation products, and they are not for everyone. For starters, they're expensive, ranging from $500 to $1,000, and the list of games slated to support the technology is relatively short at the moment. Not only that, but it doesn't look like there will be any games that support ray tracing when the first batch of RTX GPUs ship on September 20.