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Forza Horizon 4's stunning tech upgrades - and how Xbox One X shines as lead platform

DF visits Playground Games and tests the final game.

The Forza Horizon franchise has carved its own path, veering away from Turn 10's mainline series with its emphasis on arcade racing set within a massive open world. The series' evolution has been a long but often spectacular journey - a vibrant racing celebration that's given Horizon its own distinct identity and in Forza Horizon 4, Playground Games aims for something even more special from a technical perspective - a game that builds substantially on the last entry's technical strengths and focuses on Xbox One X as lead platform.

"I definitely think there's a leap in fidelity in Forza Horizon 4 over Forza Horizon 3," creative director Ralph Fulton says. "Part of that is kind of natural because Xbox One X is our lead platform. It allows us to just go into more detail. But I also think that with every run at the tech we get better at using it, we get better and more efficient at using it. Our processes and our art techniques become more refined, so I think you naturally see that it's a team who has a huge experience making horizon games, are growing in justified confidence in the way the way that they go about making a game."

Moving away from the Australian heat to a distinctly seasonable UK impacts development in many ways, providing a suitable challenge for Playground's art and tech departments. The location choice is a big starting point, and it meant visiting and meticulously rendering landmarks across the country using physically-correct properties. The landscape of the UK is carefully replicated too using a digital elevation model, giving its rolling pastures an authentic look.

"We base our original world map on DEM data, which is basically satellite height map imagery," Ralph Fulton says. "In Australia we could only buy it to a resolution of 30 metres. What that gave us was kind of a spongy height map, so you could see what was a mountain and what wasn't. In the UK though, you can get satellite DEM data to a resolution of five metres, and what that gives you is a much, much higher resolution height map which almost gives you hedge rows."

That's a lot of data to work with, but it's translated to more options for the art team. Technical art director Gareth Harwood says that this provides a ready-made base for the team's artists to work from.

"We built on the system that we had in Forza Horizon 3, a height field system that allowed us to create terrain very quickly and very easily for the artists to iterate on," he explains. "This automatically creates LODs, it creates collision for the artists as well, and it gives them more time to be artists, rather than having to worry about technical constraints in having to build our world."

DF's in-depth technical analysis of Forza Horizon 4 - it's a beautiful release.

The notion of the four seasons also provided a challenge for the team. "With seasons we needed a new way for them to be able to paint down all of the new materials throughout [each season]. We came up with a material system that allowed the artists to choose which material to paint down once, and then it would just reflect in all the different seasons," Hardwood says. "For example, if we were painting down a corn field, we could say what a cornfield would look like in spring, summer, autumn and winter, and then also how it handles, what type of pick-up you get, whether there's 3D corn on there, or whether it's all been cut away, whether it turns into deformable snow [and] what type of grip levels you get."

This impression of the UK wouldn't be complete if it were only focused on terrain though. The sky also had to be accurately modeled, along with the lighting properties that come with it. Time-lapse photography sessions lasting 24 hours were carried out, to capture the ideal skyline for each season, each time of day, and weather as well. With each switch between seasons, there's a hard cut, but from Playgrounds extensive outdoor shoots, you get the best-case from each. It's Britain with its best face.

"The assets that we end up with [amount to] 1.2TB of photography for every shoot," says CG supervisor Jamie Wood. "Every shoot that we capture takes about four weeks to process, and we end up with a HDRI image sequence. We take these images that become the sky, and obviously we also generate cubemaps for lighting, directional fog maps, cone shadow masks down on the ground. And because we're out in the field capturing real world data, we can also gather weather information, and make sure our dynamic weather is accurate."

He describes this as unprecedented work, taken to a level that hasn't been seen before in a game. That high resolution, high dynamic range sky capture then feeds into the lighting, regardless of in-game time, weather or the season. It forms a bedrock of the game's lighting, something that has been improved since Forza Horizon 3.

Performance Mode
Quality Mode
Xbox One X features two modes, with performance mode running at a fixed 1920x1080, compared to the full 3840x2160 on quality mode. You get 4x MSAA on each.
Performance Mode
Quality Mode
Dynamic lights from headlamps are removed on the performance mode to keep its 60fps output in check
Performance Mode
Quality Mode
Ambient occlusion is also dialled back, as you can see underneath the car body here.
Performance Mode
Quality Mode
Motion blur takes on a less intrusive form with performance mode selected - though undeniably the 4K quality mode gives the crisper image overall.

Playground also tells us that lighting, shadows and particularly specular highlights on foliage are improved across the board with a fully overhauled model. With Xbox One X as the lead platform, many of the engine improvements trickle down automatically to the base Xbox One. However, the bump to 4K resolution on X reveals the extent to which the team could improve this game over the last. For example, snow returns, after its appearance in the Blizzard Mountain DLC for the last game. We now have a stochastic lighting model, allowing you to see sparkles on a bed of snow. At 4K, and especially with HDR enabled on X, you get a crisp, glittering effect during Winter.

Tessellation is also a big point here. The game runs with improved tessellation on deformable snow, rendered up to 10x the quality on Xbox One X compared to the representation on the base console. Everything in sight impacts the look of it too; even wildlife passing by, but it's X that gives you the more accurate deformations as a car sweeps through. The winter season was described as a challenge by the team, but improved effects like this make it into a unique event. It transforms the existing terrain to the point it becomes unrecognizable - a new game. It marks a huge leap over the last effort at snow too, and with the car handling changes to suit.

Another area Playground Games has touched on is reflections. Cubemaps are still used across car bodies, but this time, screen-space reflections are added to the floor. In wet environments during spring or autumn, it means less work for the art team to bake in a set reflection map; instead it's all rendered based on screen visibility of lights. Artefacting is minimal too; in many games using SSR, there's a cut-off around the edges of objects in the way of a reflected surfaces. Here though, it's a tighter, more accurate form that typically avoids the problem. In this area, Xbox One X gets a 2x detail boost over the standard console.

Ambient lighting is also a new engine feature, built for Xbox One X originally, but also included in the base model's feature set. This is a volumetric occlusion technique that lets a car cast its shade of colour onto nearby buildings. There's a subtle bounce effect as you drive close to objects, and that applies regardless of machine. On top of this, screen-space ambient occlusion is at last included in Forza Horizon 4 - adding shade beneath cars and around plants and buildings. Unlike the ambient lighting, this SSAO is only enabled on Xbox One X in its quality mode.

Xbox One
Xbox One X
The Xbox One X version in its quality mode. We get a full 3840x2160 output there, compared to the 1920x1080 on Xbox One. The core visual feature-set is similar in terms of assets - though notably X gets higher quality car interiors.
Xbox One
Xbox One X
Motion blur quality is visibly upgraded on X hardware, reducing the banding artefacts we get on the base console in motion.
Xbox One
Xbox One X
Dynamic shadows from headlights is also an X-exclusive feature. Note the car straight ahead is missing the effect on base Xbox One.
Xbox One
Xbox One X
Density of foliage is increased by 50 per cent on the enhanced console, with shadow draw also seemingly improved.
Xbox One
Xbox One X
Texture filtering gets a boost on X too, with clearer surfaces at tight angles - while terrain assets themselves are blended at up to twice the resolution.
Xbox One
Xbox One X
Screen-space ambient occlusion is included on X only, with its 4K quality mode delivering shade around the car exterior.

There's a slew of feature upgrades beyond this. Anamorphic lens flares are improved in quality on both consoles, and motion blur rendering is boosted on Xbox One X to match PC's high-end settings too. Meanwhile, shadows are a match for PC's best, in terms of resolution and overall quality. One of the more exciting new features that comes to X in Forza Horizon 4 are night-time dynamic shadows. Look close, and you can see headlights and street lamps create silhouettes when cars move into their path - something only enabled on Xbox One X in the 4K mode.

Beyond this, Forza Horizon 4's tech push is more about the fine-tuning to creating a convincing British setting with more interaction than we've seen in prior Horizon titles. Physics-based destruction is enhanced this time and a stretch of beautiful hand-placed brick walls can be demolished with enough momentum - another aspect implemented for all platforms. Equally, smaller trees bend, snap and are sent flying on car impact, which gives a better sense of your presence in the world than previous games.

Xbox One X may be treated as the lead platform, but the base console is still a much-improved game technically over the last. It's a knock-on effect; many enhancements designed for the more powerful machine trickle down to the other. X is a unique proposition this time, however. With more development time behind it than the three-month effort bhind Forza Horizon 3's enhanced X patch, this game's 4K quality mode is a better showcase of how the GPU can be used.

"Because we're forward rendered we can take advantage of MSAA," Alan says. "So we've done that again, it's 4x MSAA at 4K [on Xbox one X]. It's one of the pillars for us, it's really nice to have that level of quality. We considered [FXAA], but we decided on balance to go with 4x MSAA and 4K and the graphical settings we have for Xbox One X."

The base model by comparison is undeniably a step back in image quality, but on a 1080p screen it's still imprssive. You get a native 1920x1080 with the same 4x MSAA pass, and a target of 30fps, while the bump to 3840x2160 on X hardware opens your eyes to more details. The team had to cater for this; a higher pixel count demands better quality effects and effects, where in many cases the resolution is doubled. For example, textures get a boost on Xbox One X to take advantage of the system's extra memory.

Our first look at Forza Horizon 4's beautiful 60fps mode for the Xbox One X version of the game.

"One of the things we focused on was the quality of the road texturing, and the terrain in particular," lead engine programmer Andy Sage explains. "As well as pushing the resolution to take advantage of the 4K output on the Xbox One X, we've also looked at the material quality. We have up to 2x times the number of terrain blend textures to improve the realism on the terrain. Another aspect we've improved is the blend between terrain and road to give us more realistic surfaces. The X was great here both in terms of the quality of shading, but also the increased memory." To go alongside that, foliage density is increased by 50 per cent. The practical difference in comparison isn't always visible, but having settings that match the 4K boost is a necessary must. We'll be looking into the PC version in another analysis, where an extreme settings mode could push the boat out even further in LODs, shadows and reflections. What Xbox One X gets away with here in its quality mode is bridging the gap with PC in some smart ways.

What else? Well, again, dynamic night-time shadows from headlights are only an X feature while running at 4K and 30fps, and likewise for ambient occlusion. These are missing from the base Xbox One, which otherwise gets a lion's share of the visual settings at a glance. Look close and you'll see X has a few neat extra details though, like the starburst lens flare. This added effect appears across the body work of a car during summer. On top of the anamorphic lens flares - which appear on both consoles - this exclusive X effect adds a flash of the sun's light in one concentrated spot. Again it's an effect you might only notice looking close - so it's more of a neat extra than a game-changer.

In terms of performance, the two are very nicely optimised for 30fps. There's a sense you can get the occasional one-frame hiccup every now and then - likely down to streaming. But 99 per cent of the time, Forza Horizon's 4 sticks to the series' template, building its visuals around a tightly orchestrated 30fps line regardless of scene.

Playground's work on Xbox One X began here, with the X-enhanced patch for the excellent Forza Horizon 3. The sequel takes X support to the next level.

The more fascinating prospect is the new 60fps performance mode, only available on Xbox One X. The trade-off is a drop to 1920x1080 resolution, but you once again keep 4x MSAA to clear up the image. Ostensibly, that makes the core pixel count, and image treatment, similar to a base Xbox One. However it'd be a disservice to this mode to say it regresses to base machine standards. Instead, the team describes this as optimised with as many settings from the 4K quality mode as possible, including the improved textures, foliage and lighting. Looking at a comparison between the two modes, it's very close at first glance.

Digging deeper, yes there are cutbacks. For starters you lose the dynamic headlight effect of the quality mode, plus ambient occlusion shading is dialled back as well. Otherwise, it's simply that move to 1080p that makes up the biggest difference. Slowing the footage down also reveals a less intrusive motion blur on performance mode too, which, combined with the 60fps output, can translate to a cleaner looking image during turns. There's no question that quality mode gives more detail when it's settled though, and overall has more effects going for it.

It's to Playground Games' credit that the two look so close, while still achieving 60fps. The 1920x1080 resolution is fixed of course, and when I asked the team about any chance of a dynamic res system - perhaps rising to 1440p where the X's GPU can afford it - they said it's certainly a possibility for the future. As it goes though, that 60fps target is really well met using 1080p, and it's hard pressed to drop. Again, much like the 30fps mode, there are moments in the autumn season where a few dropped frames sneak in. This isn't a half-hearted effort at all though, and Playground rebuilt from the ground up to make 60Hz a reality - and in that respect what drops you get are very rare indeed.

Playground Games' work on the Horizon series has improved with each release, and the UK location with impressive seasonal support gives the studio an effective showcase for their many technological upgrades. The last two years have been spent tailoring a beautiful, sometimes fantastical driving game that aims to surprise. Technically, it's a marvel to both look at and to play, and the end result is a gem in the Xbox One X lineup that deserves your attention.

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About the Author
Thomas Morgan avatar

Thomas Morgan

Senior Staff Writer, Digital Foundry

32-bit era nostalgic and gadget enthusiast Tom has been writing for Eurogamer and Digital Foundry since 2011. His favourite games include Gitaroo Man, F-Zero GX and StarCraft 2.

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