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Tuesday, June 11, 2019

On The Current State Of Raytracing

I imagine most people at all familiar with rendering and graphics are aware of Nvidia's recent 'RTX' technologies and Microsoft's DXR. Nvidia of course providing hardware acceleration in the form of 'RT cores' and Microsoft making the DirectX standards to use them.

We've seen pretty demo's like the Star Wars cinematic elevator video first rendered on DGX super computers then revealed to run -albeit at a far far lower level of fidelity- on consumer graphics cards in realtime.We've seen a couple games like Battlefield V, Shadow of the Tomb Raider, and Metro Exodus support raytraced reflections, shadows, and global illumination respectively.

Nvidia even recently released a mostly pathtraced version of Quake II based on a Q2VKPT open source fully pathtraced implementation.

We've also seen mention of impressive unaccelerated raytracing in cryengine using a RX Vega 56 as well as mention of raytracing on the PS5 and acceleration on Xbox Scarlet.

All these demos are quite impressive and we've even seen both Unity and Unreal engine add support for DXR in publicly available demos and betas so developers can begin to push these technologies in their applications.
It almost seems like rendering technology is suddenly accelerating at light speed. That is until you begin to look at the current situation more holistically.

The current implementations offer many substantial drawbacks that cumulatively and often individually destroy the viability of the technology.

First, performance is a huge issue. The reflection only implementation in Battlefield V absolutely demolished framerates from between 58 to 64% on the RTX 2080 and 2080 TI. The $1250 2080 TI pushing a measly "high 60s" framerate at 1080p. DXR is also limited to DX12 which particularly in the frostbite engine that BFV runs on causes serious stuttering and frametime issues. A later patch ended up improving performance after many months but that 2080 TI still doesn't manage 90FPS on high at 1080p. We're still left with a ~40% performance penalty for just those raytraced reflections.

Remedy Games themselves remarked on the enormous penalties of RTX implementations in their custom Northlight Engine. They say regarding the frametime penalties, "This is a total of 9.2 ms per frame and thus an almost one-third higher computational overhead if we take 30 frames per second as the basis". Notably, this is still at 1080p with the aforementioned $1250 2080 TI. While gamers are used to 144Hz refresh rates with frametimes well below 7ms it's hard to stomach raytraced effects that would more than double frametimes for often unsubstantial graphical improvements. Current rasterized fakery has gotten so sophisticated and convincing that raytracing just isn't as substantial as it otherwise would be.

Current RTX implementations are basically suggesting that instead of pushing 4k144 or 1440p240 like many gamers are trying to do or even stay consistent and push 4k60 or 1440p144 or even regress somewhat to 1440p60 or 1080p120 that we regress all the way to 1080p60 in the best implementations with the best consumer card currently available priced more than $500 higher than the last gen 1080 TI at launch.

We're going to need to see more than a radical improvement in performance for this to be viable in current generations games. We're left hoping that Nvidia's launch of RTX was truly so incompetent that such gains were left on the table more than 8 months after launch. Though seeing that even Windows didn't support DXR or RTX features on launch and it took months for the first game to support any RTX to come out it's not such a stretch.

Second, compatibility is horrible. Only three published games support RTX raytracing as of June 2019. Arguably Quake II could be considered if you want to include a mod. Those raytracing tools in Unity and Unreal I mentioned earlier are still in very early beta these 8 months after RTX launch with little sign of rapid improvement. Bugs are ubiquitous, backwards comparability with 1000 series GTX cards, while possible, leaves performance an order of magnitude worse than middling RTX performance. Implementation into existing projects is all but impossible at this point without limiting yourself to specific raytracing specific alpha builds of the game engine editors.

Notably, while VR is quickly becoming extremely popular with PSVR and PCVR reaching over 4 million users each and Steam getting 1 million monthly active VR users as well as Facebook launching the $400 Oculus Quest, there is absolutely no RTX support whatsoever. There isn't so much as a hint that maybe, just maybe, one of the dozen multi-billion dollar companies currently pouring hundreds of millions into VR are even considering exploring raytracing support in VR.
Obviously performance is a bigger consideration for VR as well if compatibility was even considered.

Related to compatibility, most raytracing tools are locked down from developers. While some major studios are working closely with Nvidia and Microsoft to integrate DXR and RTX into their custom game engines and indie developers will presumably get proper tools in Unreal and Unity eventually, right now there are very few options to actually modify an implementation of raytracing yourself. Current DirectX raytracing implementations often and seemly universally forgo hardware acceleration so those RT cores become moot. 

Third, as alluded to before, rasterized fakery has gotten so good that it's really difficult to justify the aforementioned issues. While realtime denoising has gotten pretty good, there are still many noticeable artifacts in all available demos. The current level of fidelity reached with these implementations falls very far short of even these established baselines in rasterized games. While raytracing will almost invariably provide more realistic lighting and effects, that doesn't mean that they will look better than rasterized games. Remedy themselves faked incredibly good looking lighting in their last game Quantum Break. Even photorealism is nearly achieved using these primitive techniques that manage to both perform so much better and offer so much better compatibility than any raytracing implementation currently available.

All of this leaves such a sour taste in my mouth regarding realtime raytracing that it's hard to imagine that it will have any real place in gaming outside of the very narrow niche of enthusiast gamers with far too much money to spend that also don't care about pushing super high resolutions, VR, or high framerates. I really do hope I'm wrong.


  1. I think Metro: Exodus is a perfect example of where RTX shines (get it?). Ray traced shadows don't really impress me because we've gotten so good at faking them. Ray traced reflections are pretty cool but not beyond a tech demo. Ray traced global illumination that's seen in Metro is, in my opinion, game changing.
    As for framerate, again, Metro is the right use-case. I own a 2080 ti and don't even use RTX for Battlefield because I only get around 80FPS@1440P which can really hinder my reaction time. But for a somewhat slow paced single player game like Metro, 60fps is completely fine. In return, you'll get some of the finest graphics you've even seen.
    I think nVidia could have done a much better job at marketing which type of ray tracing a game employs. Not all implementations are equal and it makes so much less sense to use it in a competitive shooter than a single player game. You will also notice ray traced shadows to a much lesser extent than ray traced global illumination.
    VR has a very long way to go in general for graphics and even gameplay control. We're so far away from worrying about fine graphical detail that I never even thought about RTX in VR.
    I could go on all day about RTX but I think I would end up with a comment at least the length of this article. I'll just say check out Metro because it's the best example of RTX we currently have. Plus,we have Cyberpunk, Watch Dogs, Modern Warfare, Control, Wolfenstein, and more games coming out with RTX that will give us a much better idea of what to expect. Lastly, many people find the problem to be framerate. This is something that we'll see large improvements for in the next few GPU generations.

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