When designing AI for our characters, one of the basic concepts is to have AI move with the same rules as the player. If you ever played any old racing games, sometimes the opponent cars wouldn't follow the same physics as the player, zooming along unrealistically and therefore creating a bad player experience. So, it's important to take car physics into account, including the shape of the car and four wheels, and have the AI move in the same way as the player. This is the main reason for using an AI system especially designed for autos and driving, instead of a general-purpose game AI system we have been using such as RAIN.

The driving system we'll use is Smart Car AI by BoneBreaker, which at the time of writing this book is available in Unity Asset Store for $10. It takes into account physics for the car and uses ray casting to sense the car's environment. It actually uses two systems for navigation, which are Unity's built-in navigation system to determine paths along a road and ray casting to sense obstacles and make adjustments to the car.

Additionally, Smart Car uses four-wheel physics for realistic movement. Because of the advanced use of physics, we can't just drop any car model in and have it work automatically; we will need to configure Smart Car to use the model's wheel colliders. Wheel colliders are a type of Unity's physics colliders that are specifically made for vehicles. Let's look at how to set up a car.