Xbox Series S vs ray tracing: the story so far
Support is thin on the ground - but there is promise for the future.
The Xbox Series S is, on paper, every bit as feature-rich as the Series X. It's based on the same fundamental RAM, storage, CPU, and GPU technologies - which of course means that it is ray tracing capable. You can absolutely get RT acceleration on the system, just like any other RDNA 2-based hardware platform. In practice, it's a bit more complicated. The Series S has a modest 4TF GPU paired with a meagre 10GB of RAM, which makes it challenging to implement complex ray-tracing effects on the console. Most recent games lack ray-tracing on Series S, even if they pack one or more effects on Series X and PS5.
Series S ray-tracing games are so scarce, even two years in, that you can almost count meaningful implementations on two hands. By my count there are just 15 titles in total that use hardware or software ray tracing techniques on the platform, though perhaps there are some low-profile titles we've missed (and maybe there's a case for Gears 5-style screen-space-based global illumination). While the diversity of RT titles might not be there, that's not to say that there isn't software on Series S where ray tracing isn't key to the experience - and by reckoning, there are three experiences where the technology is present and correct on the junior Xbox and works beautifully.
Metro Exodus Enhanced Edition is the standout example. The per-pixel RTGI is very high quality, realistically shading scenes and ensuring that everything looks grounded and correct within the game world. There's a consistency to the lighting that really impresses here, and is a cut above most titles that rely on precalculated solutions. Dynamic objects like characters particularly impress, with rich and grounded lighting. Stacked up against its last-gen predecessor, the improvements are hugely obvious. Metro Exodus used a real-time lighting system in prior console versions as well, although the hardware wasn't capable of handing in anything more than a relatively basic GI pass. RTGI is totally transformative to the general look of the game - and the fact we're looking at a 60fps game (albeit one that can run at a very low internal resolution) is another remarkable aspect to the game.
Compromises don't particularly stick out, though if I had to nitpick there is some fairly obvious ray-tracing noise in darker spots if you look closely. RTGI scales nicely to lower-power platforms, as you don't need much resolution at all to produce a good-looking, stable effect. That means that the ray-tracing on Series X doesn't actually look that much better here, even though technically its RTGI pass is operating at several times the resolution of Series S. There is a small reduction in visual artifacts and noise - while the higher base resolution ensures a less blurry image.
The RTGI train continues rolling with Fortnite. Late last year Epic's battle royale title was updated with Unreal Engine 5.1, and along with it came big upgrades to assets, foliage, and of course ray-tracing. On Series S, we're getting support for software Lumen RTGI - an RT solution that combines SDF-based ray-tracing alongside a screen-space GI technique to produce convincing real-time indirect lighting.
In practice, it looks quite convincing. Every area is smoothly and richly lit, which stands out in crevices and interior spaces in particular. The colourful world of Fortnite produces a lot of interesting lighting scenarios, so the RTGI has a heightened but pleasing look. Fortnite's old lighting system was simplistic and primarily real-time, with only the most basic of GI systems, and the improvement stands out in basically every shot. The primary compromise inherent to Series S again comes down to resolution. Lumen's software RTGI targets just 1/16th resolution on current-gen consoles, which doesn't seem like it would play very well with Series S and its 720p-class internal render targets. But again, RTGI looks solid even at cut-back pixel counts, and the lighting still feels accurate enough to produce an excellent result on Series S.
Denoising can only do so much here, though, so splotchy noise patterns are a common sight in darker areas that rely on indirect lighting. Plus, the RT reflections that are present on other current-gen platforms are gone, replaced with a less stable though still good-looking screen-space technique. Series S does manage to acquit itself quite well here in general though, producing a hugely satisfying RT implementation.
Unreal Engine 5 got its first playable debut on consoles in the stunning The Matrix Awakens sample released in late 2021. This is a demo, not a full game, consisting of an 8-minute cinematic sequence and an explorable open world city area, though the final results are just too good to exclude from this rundown. Series S gets the full ray-tracing treatment - hardware-based RTGI, plus ray-traced reflections, as well as RT shadows in select moments. The final visual results look incredible, particularly in the opening cutscene segment, which should be abundantly clear to anyone who's seen it. But the consistency and quality of the ray-tracing is made clear once you have full control in the open world.
RTGI lends the game stable, true-to-life lighting, even on character models and in tough spots like the underside of bridges. It's a bit subtler than something like Fortnite, but it's still very effective. Reflections look great as well, adding detailed, perspective-correct reflections that would be very challenging to represent in real-time using other techniques. Series S takes a step back from the other console versions again here, though there aren't any obvious feature cuts. RTGI quality is somewhat lower though it's not too noticeable - noise isn't a distraction, though the RT becomes more detailed as you approach and you can sort of break it momentarily by approaching at speed, though this is also apparent on other console platforms.
The reflections are more visibly downgraded. Stacked up against Series X, the game representation in the BVH is scaled back a bit, with simplified textures and models. It only really stands out on close inspection though, and only when screen-space information is absent. Diffuse surfaces show a more meaningful quality hit, with a messy and somewhat unstable resolve, though these are mostly based on screen-space reflections so the RT isn't as much to blame.
My second grouping of Series S RT titles might look strange, but essentially it is a quartet of Capcom games: Resident Evil 2 and 3 Remake, and Resident Evils 7 and 8. All pack very similar ray tracing tech courtesy of the aptly named RE Engine. Essentially, these games offer RT reflections plus a limited form of RTGI, which essentially solves certain lighting errors and issues present in the pre-existing baked GI solution without fully replacing it.
Reflection quality varies quite a bit depending on the circumstance. Well-lit outdoor areas expose the simplicity of the BVH and can look significantly worse than the screen-space reflection and cubemap techniques that are otherwise used. But indoor spaces often look reasonably good. The third person Resident Evil remakes make better use of the reflections in my view, with their artificial, city-type environments. RT resolution is quite low and suffers from a lot of noise across all titles, however, so the results can be messy.
The GI produces more subtle but appreciated improvements to lighting accuracy. Some of the light bleed that is present using rasterised lighting has been fixed, and light does have more realistic propagation through certain scenes. This is mostly evident on smaller bits of geometry, which can otherwise lack accurate bounce or exhibit odd shading. Baked GI looks good for the most part in these titles and the RTGI does a reasonable job of fixing its more noticeable problems, so it's a solid solution.
Series S handles the RT quite effectively in my view, taking a moderate hit to reflections quality relative to Series X but otherwise managing to look pleasing enough. This does have some serious performance implications, unfortunately, which make RT a far less appealing option compared to the other consoles, where the hit to frame-rate is not so pronounced.
My third grouping consists of Unreal Engine 4 titles. UE4 has easy-to-implement RT features, which means that quite a few titles based on the last-gen Unreal Engine tech use ray tracing on consoles. The vast majority of these drop RT on Series S, but there are a few exceptions. Hellblade: Senua's Sacrifice got an RT enhancement in 2021 that did extend the RT olive branch to the Series S release as well. Ray-traced reflections here do look quite detailed and present clean edges free of screen-space artifacts.
The primary issue is that Hellblade makes heavy use of fog and volumetric lighting, which don't seem to get any sort of approximation within the BVH structure used to calculate the RT effects. This means that the screen-space reflections look significantly more accurate a lot of the time. The Series X suffers from the same issues here, producing a bit of a mixed result for the ray-tracing. Obviously the SSR can be occluded if the camera is positioned at an acute angle, but the rest of the time the screen-space results often look comparable or better.
Deliver Us The Moon also suffers from an unsatisfying RT implementation in my view. This indie space-based puzzle game uses RT shadows on console, in a hybrid implementation that blends ray-tracing based shadows with traditional shadowmaps and baked shadows. The RT shadows do look interesting, and are clean and detailed in a way that would be very challenging to represent with typical shadowmap techniques in real-time. But actual shadows in a lot of the lighting situations in the game should look more diffuse, like when cast from a close light source or a scattered source like an atmosphere-diffused sun. These stencil-style shadows are relatively cheap and do add nice bits of shadow coverage for some smaller objects, but I mostly prefer the traditional shadow techniques.
Plus, there seems to be a bug where character shadows are essentially not cast at all with RT turned on, which looks ugly. The developer did report that RT reflections are present on current-gen consoles as well, but I couldn't find any evidence of this in my testing, on either Series S or X.
Little Nightmares 2 has a nice bit of ray tracing, although it's fairly subtle. Across both visual modes RT reflections do seem to be enabled. Quality does take a big hit in the performance mode, but neither of the two options has visible disocclusion artifacting in the reflection itself, indicating an RT technique is in play. The initial Xbox Series version of the game only featured SSR, but RT seems to have been patched in subsequently. This particular game uses reflections sparingly however and features relatively few glossy surfaces. I had to play about halfway through to work out if RT features were enabled at all, as they are practically non-existent until the hospital level. And the camera has a semi-fixed perspective, which would minimize typical SSR issues.
Observer: System Redux also sports RT reflections on Series S, though they only seem to apply to very glossy surfaces. Scene coverage isn't great, though the occasional RT highlights do add to the presentation - and you're still getting 60fps gameplay here as well.
The final grouping consists of unique titles that have odd or novel RT implementations. Crysis Remastered leads this pack, with a software-based spin on RT reflections that actually debuted first on last-gen consoles. The ray-tracing looks decent in stills here, though it does tend to take a second or two to cohere after movement. Both RT range and coverage are pretty limited, but the results are surprisingly strong for software-based ray tracing.
The two most recent Formula 1 racing games - F1 2021 and 2022 - also have ray-tracing features. RT shadows and reflections are present in both titles, but only in the pre-race warm-up segments and in the "My Place" feature in F1 2022. During gameplay, there's zero RT whatsoever. Forza Horizon 5, in a similar vein, has ray tracing features in select moments. By entering the Forza Vista car viewer in the game's quality mode, you can see accurate RT reflections across car bodies. The results are sublime, though this unfortunately doesn't extend to gameplay, which relies on a real-time cubemap solution for vehicle reflections.
Finally we have Watch Dogs Legion, which features an option for RT reflections. This is actually one of the stronger RT implementations on Series S, with accurate reflections added to glossy surfaces. There are a few obvious quality compromises - the reflections do suffer from quite a bit of ghosting and aliasing, which is particularly noticeable on car bodies. Plus, the RT falls back to a cubemap-based solution for distant detail. In general though, the coverage is pretty solid and it does make a big difference when traversing the streets of London.
So we've proven that RT can work on Xbox Series S - and it can be transformative. To see a 4TF GPU produce quality along the lines of Metro Exodus, The Matrix Awakens or Fortnite is quite the feat. However, ray tracing is a very demanding process and that is obviously a factor on more limited hardware platforms like the Series S, but the greater issue is the lack of RAM on the system. With 10GB of RAM - of which around 8GB is available for developers - there's little room to store the complicated acceleration structures that make real-time ray tracing possible in the first place. BVHs can take up a lot of area in memory, which the Series S doesn't have room to spare in a lot of cases. RT can be delivered effectively on the console, but clearly a lot of work is required to make it happen.
Ultimately, that means that most games I found that support ray tracing simply don't support the feature on Series S. Titles like Control, Cyberpunk 2077, Chernobylite, Doom Eternal, Grand Theft Auto 5 and Guardians of the Galaxy don't have ray tracing on Series S, unlike Series X and PS5. Ray-tracing is a relative rarity on Microsoft's junior current-gen machine, with just a few standout titles making effective uses of RT techniques.
And the games that do use RT are often best enjoyed without it. The 30fps vs 60fps split for RT and fully rasterised modes is very typical on the console and given the choice, it's rare that I'd choose an RT-based quality mode over a 60fps performance alternative. The Resident Evil titles suffer particularly from this issue, with a wobbly 30-40fps frame-rate in their ray-tracing modes. There are exceptions of course - like the brilliant-looking Matrix Awakens, or the 60fps-targeting Metro Exodus and Fornite - but it's often a better choice to enjoy lower input lag and more fluid animation over an implementation of ray tracing that usually doesn't bring a transformative improvement to the presentation.
Perhaps this will change in the future. Some ray tracing techniques, particularly RTGI, require a lot of work to use alongside a non-ray traced fallback for higher performance modes, or for weaker hardware. If a title is designed around RTGI, the developer really has to find a way to run that technique on the Series S, regardless of the effort they have to expend or compromises they have to make. Other RT effects, like those that replace screen-space traced techniques like SSR and SSAO, are easier to strip away for a Series S build if needed, but a heavy use of per-pixel RTGI would be tough to replace without totally ruining the visual presentation on the S or doing a lot of duplicate work. So it's best to assume that games using RTGI will probably retain those effects on Series S, even if that means cutbacks elsewhere.
So where are left at the end of this comprehensive rundown? The Series S is a ray tracing capable console - but outside of a few highlights (one of which is a demo rather than a game) it clearly has a mediocre track record in existing software, mostly down to a combination of a less capable GPU and restricted memory and memory bandwidth. With that said, however, it's heartening to see both hardware and software RT deployed so successfully with Unreal Engine 5. While it's not a lock for every UE5 game in development, at least the template is there to demonstrate that Series S can deliver on the premier middleware of the coming generation.
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