Ray tracing
Also known as: real-time ray tracing, raytracing
Ray tracing is a way of creating computer graphics by simulating the paths of light rays as they bounce off, pass through, or are blocked by objects.
It produces realistic reflections, soft shadows, and lighting that older techniques can only fake. While film studios have used ray tracing for decades, real-time ray tracing in games only became practical around 2018, and it still costs so much performance that most games mix it with faster tricks.
Ray tracing, explained at three levels
At home
Think of shining a flashlight in a dark room and watching where the beam lands, bounces, and gets blocked. Ray tracing does the same thing with maths. The computer fires imaginary rays of light into a 3D scene and follows each one as it hits surfaces. Where a ray bounces off a puddle, you get a reflection; where something blocks it, you get a shadow.
At work
Ray tracing is a rendering method that calculates lighting by following simulated light rays through a 3D scene instead of approximating it. Because reflections, shadows, and light bouncing between surfaces come out physically correct, the images look photographic. Businesses care because architects, product designers, and film studios can show clients accurate lighting and materials before anything is built or shot.
At home
Ray tracing usually works backward, from your eye instead of from the lamp. For every pixel on your screen, the computer sends a ray from the camera into the scene. When that ray hits a surface, it sends more rays: one toward each light to check for shadow, one bouncing off for reflection, and sometimes one passing through glass. The colours those rays bring back decide what the pixel shows. That's why a ray-traced puddle can reflect a car parked behind you.
At work
In real-time work, ray tracing is rarely used alone. Most games and visualization tools use hybrid rendering: rasterization draws the base image quickly, then ray tracing handles specific effects such as reflections, shadows, or global illumination, which is light bouncing between surfaces. Each effect has its own ray budget. Because that still costs a lot, upscalers such as Nvidia DLSS, AMD FSR, and Intel XeSS render at a lower resolution and rebuild a sharper image, winning back the frame rate.
At home
The hard part of ray tracing isn't bouncing light; it's finding which object a ray hits first among millions of triangles. Testing every triangle would take forever, so the computer organizes the scene into a bounding volume hierarchy, nested boxes that let a ray skip whole regions it misses. Since 2018, graphics cards have had dedicated RT cores that walk these boxes in hardware. While raw GPU power gets the credit, in my opinion that clever bookkeeping is what made real-time ray tracing possible.
At work
Real-time ray tracing runs on APIs such as DirectX Raytracing and Vulkan Ray Tracing, which split work into ray generation, hit, and miss shaders over an acceleration structure. Frame budgets allow only one or two rays per pixel, so the raw image is grainy and must be cleaned by denoisers, increasingly AI-based ones like Nvidia's Ray Reconstruction. Moving objects force acceleration structure rebuilds, which cost time and memory. Teams should keep a rasterized fallback, since many players still lack capable hardware.
Real-world examples
At home
Marcus turned on ray tracing in a racing game and noticed cars now reflected the buildings and streetlights around them. His frame rate dropped until he also enabled upscaling, which brought it back.
At work
Nadia is a visualization artist at a Toronto architecture firm. Using ray-traced rendering, she shows clients how sunlight will move through a planned atrium at different times of year, helping them choose window placements.
How it compares
| feature | Ray tracing | Rasterization |
|---|---|---|
| How it works | Simulates light paths | Projects triangles onto the screen |
| Realism | High, physically based | Relies on approximations |
| Performance cost | High | Low |
| Typical use | Films, high-end games, visualization | Nearly all real-time graphics |
Ray tracing is more realistic. Rasterization is much faster.
For analysts
For visualization work, ray tracing can reduce costly physical mockups. I'd weigh the hardware investment against how many client decisions depend on seeing accurate lighting before construction or production.
History & origin
Arthur Appel described casting rays to determine shading in 1968, and Turner Whitted's 1980 paper showed recursive ray tracing for reflections and refractions, producing famously realistic images that took hours to render. Pixar and other studios adopted ray tracing for films in the 2000s as computers grew faster; Pixar's Cars (2006) was an early showcase. In 2018, Nvidia launched its RTX 20 series graphics cards with dedicated ray tracing hardware, and Microsoft added DirectX Raytracing to Windows. The PlayStation 5 and Xbox Series X brought ray tracing to consoles in 2020. In my view, real-time ray tracing only became truly usable once AI upscaling arrived to pay for its performance cost.