Art of Roads in Games
This article explores the often-overlooked technical intricacies behind rendering realistic roads in city-builder games. The author delves into why common game development techniques, like Bezier splines, fall short compared to real-world civil engineering principles like circular arcs and clothoids. It's a deep dive into computational geometry and practical engineering, appealing to HN's audience interested in game development and problem-solving.
The Lowdown
The author, a long-time city-builder enthusiast, shares a deep-seated fascination with road networks, both in games and the real world. This curiosity led them to investigate the underlying mathematical and engineering principles that make roads look and function realistically, revealing a fundamental disconnect between common game development approaches and civil engineering best practices.
- Early city-builder games (SimCity 2000, SimCity 4) offered limited road-building options, gradually improving with features like elevation and curved roads.
- Cities: Skylines introduced significant freedom for road placement, but even with extensive mods, the author noticed persistent issues like unrealistic bends, sharp turns, and incorrect corner radii.
- The core problem identified is the widespread use of Bezier splines in game development to define road paths.
- Bezier splines, while elegant for many applications, fundamentally fail to preserve shape and curvature when offset, leading to "pinching" and self-intersecting geometry in tight road turns.
- In contrast, real-world road engineering often relies on simpler, more robust geometric primitives like circular arcs, which inherently maintain parallelism when offset and simplify intersection calculations.
- For high-speed roads, civil engineers employ advanced "transition curves" like clothoids, which smoothly increase curvature, ensuring comfortable and safe transitions for vehicles, though these are computationally complex.
- The author built their own road system, driven by curiosity and the desire to provide better, more realistic solutions for indie game developers than currently available assets. Ultimately, the author highlights how real-world engineering constraints, often considered "kindergarten math" (like circles), offer superior solutions for realistic road rendering compared to more complex computational geometry. They plan to share their technical implementation in a future blog post, aiming to elevate the standard for road design in city-builder games.