Ray tracing is the general technique of following rays of light through a scene. Path tracing is ray tracing taken all the way: every pixel's light is computed by following complete random bounce paths.
- What games call ray tracing is usually a hybrid: a normally rendered image with one or two ray traced effects layered on, such as reflections or shadows. Path tracing replaces the whole lighting model.
- Path tracing looks more correct because nothing is approximated, and it costs far more because every effect is computed for every pixel with many samples.
- For a benchmark, path tracing is the more honest load. There is no cheap path, no denoiser to hide a slow card, and the work per sample is identical on every machine.
- SystemCheck's path tracing stage runs in the browser and reports samples per second, so you can see how your card handles the heavier of the two without installing anything.
Two words for one idea, at different depths
Ray tracing means following the path of a ray through a scene to see what it hits. That is the whole definition, and it is old: it was used for shadows and reflections in offline rendering decades before graphics cards could do it. Path tracing is a particular way of using ray tracing, where each pixel's colour comes from following complete paths of light, bounce after bounce, chosen at random, and averaging many of them.
So every path tracer is a ray tracer, but most things called ray tracing are not path tracing. The difference is how much of the image is computed by following rays, and how many bounces are followed.
What games mean by ray tracing
A game with ray tracing switched on still draws the scene the traditional way, by rasterization: geometry is projected to the screen and shaded with fast approximations. Then one or two effects are replaced with ray traced versions. Ray traced reflections fire a ray from each shiny surface to find what should appear in it. Ray traced shadows fire rays towards the light to see what blocks them. Ray traced ambient occlusion fires short rays to find nearby corners.
Each of these traces a single bounce, or sometimes none, and only for the pixels that need it. That keeps the cost manageable on a card with dedicated ray tracing hardware, and it is why turning on ray traced reflections might cost a third of your frame rate rather than all of it.
What path tracing changes
A path traced game does not rasterize the lighting at all. For every pixel, several paths are traced from the camera, each bouncing a few times, and their results are averaged. Direct light, shadows, reflections, ambient light bouncing off walls and light bleeding colour between surfaces all come from the same calculation. There are no separate effects to enable, because there is only one effect: light.
A handful of samples per pixel per frame is nowhere near enough for a clean image, so a path traced game relies on a denoiser to smooth the result and usually on upscaling to reduce the pixel count. That is why path tracing modes in games are tied to the newest cards and to upscaling being on.
Which looks better, and what it costs
Path tracing looks more correct, because nothing is faked. Shadows soften with distance the way real shadows do, reflections include reflections of reflections, and a bright wall lights the room around it. The hybrid approach approximates each of these, and the approximations show in places: light leaking under objects, reflections that stop at the edge of the screen, rooms that are evenly lit when they should not be.
The cost difference is large. A hybrid game with ray traced reflections might run at two thirds of its rasterized frame rate on a capable card. The same game in a full path tracing mode can run at a fifth or less before upscaling and frame generation are used to claw it back. On a card without ray tracing hardware, path tracing in a modern game is not practical at all.
Which one makes the better benchmark
A hybrid ray tracing benchmark measures a mixture: mostly rasterization, with some ray traced work whose share depends on the scene. Two cards can trade places depending on how much of each a given test contains. A path tracing benchmark measures one thing, the cost of a sample, with the same work on every card and nothing to hide a slow result.
That is why the SystemCheck run ends with path tracing rather than a hybrid scene. The stage renders a small scene at a fixed 960 by 540 with one path per pixel per sample, times every sample to completion, and keeps the card loaded for the whole stage. The result is samples per second and how consistently they arrived, which is a direct reading of sustained shader throughput.
It runs through WebGL2, so there is no ray tracing hardware involved. A card with dedicated ray tracing units does not get a free advantage here; it is measured on the same general compute as every other card. That makes the figure less flattering for the newest cards and more comparable across all of them.
Terms used here
Questions
- Is path tracing better than ray tracing?
- It is more complete. Ray tracing in games usually means one or two ray traced effects on a normally rendered image. Path tracing computes all the lighting by following full light paths, so it looks more correct and costs far more. Better depends on whether your card can afford it.
- Do I need an RTX card for path tracing?
- For path tracing modes in modern games, yes, in practice: they depend on dedicated ray tracing hardware plus a denoiser and upscaling. A browser path tracer is different, since it runs as a shader on any card with WebGL2, which is what lets the SystemCheck stage run on integrated graphics.
- Why is path tracing so much slower than ray tracing?
- Because it replaces every lighting calculation with traced paths and needs many samples per pixel to converge, while hybrid ray tracing traces only a single bounce for one or two effects and leaves the rest to fast rasterization.
- Which is a better test of my graphics card?
- Path tracing, for a sustained throughput test: the work per sample is identical on every card and there is no denoiser to hide a slow one. Hybrid ray tracing tests are closer to how a specific game behaves, but their result depends on the mix of effects in that scene.