Playground Games, the developer of Forza Horizon, has undertaken a hefty technical task inheriting Turn 10's Forza codebase, the developers said in an interview with Eurogamer.
Speaking in an in-depth interview with Eurogamer's Digital Foundry, Playground Games' technical director Alan Roberts, lead gameplay engineer Karl Hammarling and lead rendering engineer Andy Sage talked Eurogamer through the process of developing Forza Horizon, from the initial pitch in 2010 to working with Turn 10 as the studio made its first Forza game.
The three developers dove into the nitty gritty of the game's code, explaining what it was like working with Turn 10's game engine.
"We built the game around the Turn 10 engine, as we were really keen to retain the Forza DNA, such as the car physics engine," Roberts said. "It was surprisingly quick to get started, but we were making some pretty fundamental design decisions that required serious divergence, so in some ways we have completely changed the architecture."
One such change is the streaming of cars in Forza Horizon. Another is the renderer changing to 30 frames-per-second from Forza 4's 60 FPS while keeping all the physics simulation systems and AI updating in the same way.
The developers go into detail about using post-processing motion blur based on per pixel velocity to improve smoothness and how the streaming system was developed in order to cope with the multiple driving routes and large open spaces.
The full interview can be read at Eurogamer.