fourmilab / flocking_birds

Realistic simulation of flocking birds for Second Life in Linden Scripting Language

Fourmilab Flocking Birds

Fourmilab Flocking Birds is an artificial life simulation based upon the "Boids" algorithm developed by Craig Reynolds in 1986. The product provides an egg-shaped deployer which is controlled by commands in local chat. It will randomly hatch (either confined to the two-dimensional X-Y plane or in three-dimensional space) a flock of individual birds which, independently fly, sense the position and motion of nearby birds, and obey five simple and identical rules:

1. Turn away from the edges of the "cage" in which they are confined.
2. Obey a limit on their maximum speed.
3. Fly toward the centre of mass of nearby birds.
4. Avoid collisions with nearby birds.
5. Try to match the average velocity of nearby birds.

All of the parameters which govern these rules, such as the visual range within which birds can sense one another and the strengths of the various behaviours can be set by commands in local chat, either before the birds are hatched or while the simulation is running. Each of the rules can be independently enabled or disable to observe how they affect behaviour. Other than distributing these settings, there is no central control: each bird is entirely autonomous and controlled by its own script and what it senses within its visual range.

Despite this simplicity, a flock of these birds exhibits complex emergent behaviour which mimics that of real birds. It demonstrates how complexity and order spontaneously emerge from simple rules without top-down control. Other than the initial random assignment of bird position and velocity, the simulation is completely deterministic: there is no randomness in the behaviour of the birds, and yet the flock appears to be acting with free will and patterns never repeat.

This repository contains all of the software and resources, including programs in Linden Scripting Language, textures, notecards, and development documentation, tools, and resources used the model and its development. The actual model is built within Second Life and these components are installed within it.

The complete model is available for free in the Second Life Marketplace. This repository contains everything in the model (except the prims, which are objects built within Second Life), plus additional resources for developers who may wish to extend or adapt the model as they wish. The model is delivered with "full permissions": those who obtain it are free to copy, modify, and transfer it to other users within Second Life.

All of this software is licensed under the Creative Commons Attribution-ShareAlike license. Please see LICENSE.md in this repository for details.