Reflecting on Real Time Ray Tracing


Uneal Engine real time ray tracing demo of three star wars characters in a lift

Unreal's latest real time ray tracing reflection demo

So, you may have already seen Unreal's veeery impressive demo showing off real time reflected rays (if you haven't there is a link at the end of this short article). If you're working on CG or have a passion/hobby in this area, then no doubt the thought of being able to render everything in real time (the demo boasts 24 fps) as opposed to hours per frame must sound like a dream come true right?


Certainly watching the demo, you can see that there is what appears to be legitimate ray tracing of reflections. Take a look in the image above and you can see the reflections in Captain Phasma's armour of the lights in the ceiling and also of the two storm troopers. In the video you can see those reflections move as the storm troopers move, awesome!


So, no more long renders or render farms right?


In the future this certainly seems possible, though its important to recognise one important fact (there are lots more coming in this article, but this is the BIG one). The demo you see here is running on a server grade Nvidia box worth $150'000. This piece of gear packs 4 of Nvidia's latest Volta based V100 cards for a total processing power of 1000 TFLOPs!! To put this in perspective, for the money you could buy 50 Titan V cards.


Powerfule GPU by nVidia


I'm just guessing here, but I'm fairly certain that putting 50 Titan V cards together would give you real time performance in ordinary ray tracing engines, for SOME things. Thats another important distinction to make, the demo only talks about reflected ray tracing, no refraction, sub surface scattering or heaven forbid, caustics.


Whats more the demo also restricted rendering of Rays to certain parts of the scene, with the walls being rasterised (which is how game engines draw 3d objects and is markedly different i.e. faster than ray tracing).


Spoiler, real time ray tracing is not new


In some ways the demos going around on the internet now seem to have completely reset our collective memories of the fact that we've seen real time reflection ray tracing before, its been in existence for quite a few years now; going by a casual google search on the subject. Here's nVidia's state of the art demo for their Kepler architecture some six years ago.