Boids is an algorithm for simulating natural group flocking behavior. Flocking is an emergent behavior accomplished by applying a set of simple rules on autonomous agents, called "boids". Each boid operates independently, assessing its surrounding flock and adjusting its heading based on an evaluation of a set of basic rules.
The standard flocking rules:
1. Cohesion: Steer toward the average position of nearby agents
2. Alignment: Maintain a heading similar to the average heading of nearby agents
3. Separation: Steer away from agents that are close to avoid crowding
In addition to the standard flocking rules, I've added:
4. Bound: Steer away from the bounds of the device screen to keep agents in view
A touch adds a temporary rule:
6. Seek: Move toward the current touch position
A force touch adds a temporary rule:
7. Evade: Move away from the current touch position
// Initialize and add a Boid SpriteNode to the Scene
let boid = Boid(withCharacter: "🐡", andSize: 40)
addChild(boid)// Configure the boid's behaviors.. or don't; whatever, it's your life
self.behaviors = [Cohesion(intensity: 0.1), Separation(intensity: 0.1), Alignment(intensity: 1.0)]Because each boid needs to iterate over the entire group, this runs in quadratic time O(n²). As a benchmark, the iPhone X can maintain 60fps when simulating up to 150 boids.
- Xcode 10.1
- iOS SDK 12
- Swift 4.2
Original Paper: Craig W. Reynolds (1987). Flocks, Herds, and Schools: A Distributed Behavioral Model
Pseudocode: Conrad Parker (2007). Boids Pseudocode