Playground built the game while building the studio, but with so much of Turn 10's tech in Horizon, Microsoft's Seattle racing studio get a joint developer credit on the title. "We've done quite a lot of work to the engine," says Fulton. "We took the graphics engine, we took the physics system and we took parts of the driver AI but we had to add a lot on top because we're making a completely different game, both in the sense of the experience you get and the technical demands on the Xbox."
The only concession made along the way was a hit to Forza's signature sixty frames per second. Somewhere between Forza 4 and Horizon, Playground dropped the framerate down to 30fps with motion blur to smooth out the action. In exchange, they've built hundreds of miles of open road in a fantasy version of Colorado. "It's like a mix tape," says Greenawalt. "It's got red rocks and mountains and rivers and tonnes of diversity all squeezed into one area."
"You won't believe the views in Colorado," says Fulton. "We knew we had to invest a lot in the technology to bring those vistas to life. Now, if you've played Forza 4's Bernese Alps track you'll be no stranger to great vistas, but the difference in Horizon is that if you can see it, you can drive it. We had to create what we call 'Uber LOD' tech for the game to draw twenty kilometres into the distance while retaining the high fidelity world."
Horizon's Colorado is home to mile-long curves, off-road dirt tracks, jaw-dropping elevation changes, and the Horizon festival - a racing/music event in the heart of the state where you can paint your car, buy new ones, or enter events. The Horizon festival is easy to find - roadside banners will always guide you home and its searchlights and laser shows are visible from miles away when night falls. Horizon is the first Forza to feature night racing, and once again, it's Turn 10's maths that make it work.
"When we knew we had to create an open world, we knew we had to have a time of day system," says Fulton. "That's just the price of entry for the open-world setting. But we were fortunate because Forza gives us this image-based lighting system which sits the car in the scene - the lighting is real, not baked-in. So we have a dynamic sky and cloud system, atmospheric scattering, the sun is dynamic and casts dynamic shadows, and when you're driving at night the whole driving experience is changed. These are dark, dark roads lit only by your headlights, so the driving experience in Horizon is always changing."