Hardware accelerated ray tracing is now firmly established in triple-A titles on PC and with the transition to next generation Xbox and PlayStation hardware, consoles can now join the party. Watch Dogs: Legion is the first DXR-enabled title we've seen that also features ray tracing on consoles - which raises the question: to what extent can the new machines match up to existing PC hardware? What kind of compromises are required to bring RT to consoles - and what happens when we retrofit those cuts to the PC version? Let's just say that the answers are illuminating.
Hardware RT in Watch Dogs Legion is used for reflections, replacing the standard system based on a combination of screen-space reflections and cube maps. To make that clearer, cube maps are essentially non-dynamic 'probes', capturing environment detail and baking them into a texture wrapped around a cube - and typically thousands of them are generated in any given scene, drawn upon when needed by the game engine. Screen-space reflections capture what's on-screen, mapping that information into reflective surfaces like glass walls and puddles. This combination is often convincing enough but is rarely satisfying in reflecting moving objects (like people milling around the city) or in showing detail that isn't currently on-screen. Ray tracing is expensive but solves all of these issues - and Marvel's Spider-Man: Miles Morales is the best console rendition we've seen to date, up to a point.
Watch Dogs: Legion perhaps lacks the full RT spectacle of Insomniac's efforts but it does have its own plus points. Unlike Spider-Man, there are reflections within reflections, so the reflection of a puddle on the ground, for example, will show reflective properties. Also, the geometry in reflections looks to be the same level of detail and precision as those in the primary view - Miles Morales has a lower precision 'RT city' from which to draw its reflections. However Ubisoft's implementation also has plenty of similarities with the PS5 exclusive. Xbox Series S and X are using stochastic reflections much like Insomniac's tech, so they will technically produce more realistic surface reflections than other simpler types of ray tracing. Also, the ray traced reflections in Watch Dogs: Legion add to transparencies - so glass materials look very realistic. Put simply, it's a big upgrade from a visual perspective, especially for a cityscape rich in reflective surfaces.
Hardware RT is computationally expensive and right now the consoles have no AI upscaling technologies like DLSS available to mitigate the performance hit and this presents a problem. Even on my optimised settings, the PC version of Watch Dogs: Legion was managing just slightly above 30fps with ray tracing set to the lowest setting at 1440p internal resolution when using an RTX 2060 Super. Series X renders with dynamic resolution scaling between 1440p and 2160p, with Series S coming in at 900p to 1080p. So how is Ubisoft achieving this? Is it a fully featured RT implementation comparable with PC? Well, the answer is no - and we know this not just from our eyeballing but also from the Watch Dogs: Legion PC version, which rather helpfully contains all of the settings data for every rendition of the game.
The consoles do a lot behind the scenes to turn off elements not found in the PC game's menu, like disabling headlight shadows on cars, using half resolution global illumination passes and reducing shadow quality. There's no high resolution texture pack (not even on Series X, S fares even worse) on top of many other compromises. For ray tracing, a checkerboard rendering approach is used for all systems - even PC - so what are effectively half resolution RT reflections on PC become quarter resolution on Series X, calculated at 1080p, reducing to 720p on Series S.
In addition to that, cutbacks found on PC at lower RT settings are also included - like no reflections for dynamic particles or projected decals. Meanwhile, screen-space reflection fallbacks are of a lower quality. The biggest optimisation beyond internal resolution is the roughness cut off. Basically, on Series S and X, the rougher materials in the scene - like duller metals, marble, polished tiles and the like - do not receive ray traced reflections and fall back to cube maps more readily. In this sense, consoles are lower than PC's medium (ie lowest) RT preset. It's a smart optimisation really: the fewer reflective surfaces, the less work the GPU needs to do and the more performant the RT system becomes.
Thanks to some modding magic, we can import all of these additional compromises back into the PC game - except for dynamic resolution scaling. There are also minor differences in the filtering quality of the RT reflections, so PC still remains a touch higher in fidelity terms. However, overall, it's very, very close. With this in mind, I thought it would be interesting to see just exactly what GPU is needed to get comparable performance to the Xbox Series X and to do that, I found an area of the game where I saw the Xbox Series X have a countable resolution below 4K, meaning that the Xbox GPU is saturated. Loading up that exact same scene on the RTX 2060 Super at native 4K, the GPU hits 32fps in this scene, so it is running above 30fps at a higher resolution than the Microsoft console. In fact, just walking around the game world it is possible to see how the RTX 2060 Super is actually good at getting above 30fps at native 4K, though I expect that dynamic resolution scaling would be needed to get an absolute 30fps lock across all content.
I came away from this testing with several conclusions. We may well be seeing a different level of scaling from AMD's console GPUs with RT enabled. After all, in the non-RT Gears 5, an RTX 2080 is said to be comparable to Series X, yet here in Watch Dogs: Legion with RT features active, an RTX 2060 Super seems to be more performant. This means that consoles may require reduced resolution, distance, or material settings compared to mid-range PC graphics hardware. As for Ubisoft taking all of the console compromises and porting them back to PC, I'd say that this may well be a worthwhile option depending on how AMD RDNA 2 cards run the game.
With Nvidia tech, there's no real need to reduce RT settings lower than medium - turn on DLSS and you get performance back that mostly covers the hit RT incurs. However, with that said, I found the test highly enlightening and I would love for PC versions to feature console configurations as an option - it would be great for our analyses, but more importantly it would greatly benefit users who just want an easy console-like experience without having to think about graphical settings too deeply. After all, consoles typically deliver the best bang for the buck and those optimisations do tend to transfer across nicely to PC as well.
Of course, it's important not to take too much away from this very early test. After all, this is just one game - and a launch title at that, likely finished in an accelerated window of development with non-final tools and console APIs. We will return to Watch Dogs: Legion to investigate PlayStation 5, but we can offer up some spoilers based on the in-game config files. They suggest that 'Prospero' (the development codename for PS5) features identical settings across the board compared to 'Anaconda' (Xbox Series X) and if that's the case, it may be just performance or dynamic resolution scaling quality that separates the two machines. We'll report back on that as soon as we can.
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