The Chaos game engine

What would game development look like if the engine made it as simple as possible?

• It would probably use a variant of ECS
• It would be Functional (as in functional programming)
• Devs wouldn't require deep knowledge of engine internals to use it;
• But, the engine internals should be easy to learn in depth.

Ideally, in addition to the previous goals:

• The technology should facilitate cross-platform development.
• On the fly additions/changes to game code should be seamless. (No lengthy recompilation)

The chaos engine was borne to achieve these goals.

Getting started

todo

Engine Architecture

• Sparse Sets are used for component storage.
• To be pure functions, our systems must be free of side effects. They therefore have to return the effect of running them. In the Chaos engine, systems are functions which take in the existing World state as a parameter, and return a series of Commands to apply to that World. e.g. informally, a command might say "Add component HP(3) to entity with id 1", but it doesn't have any notion of actually applying that to the World. It is therefore fully declarative.
• Systems are grouped into stages which run sequentially based in the inter-stage dependencies.
• Within stages, systems are run in parallel based on their dependencies.

Examples

Take a look at snake.cljc within the examples folder.

Game lifecycle

When the game runs, it follows a set stage ordering:

• Once per game, the :start-up and :tear-down are run, at the beginning and end of the game respectively.
• In between these stages, the game will continually step forward until it detects that the game is over.
• A :pre-step stage and :post-step stage run before and after each step, respectively.
• Similarly, for each stage, a :pre-stage and :post-stage stage are run.
• Of the remaining stages, the :update stage is run first.
• Then, each of the remaining stages is run in order, based on their dependencies.

Example Lifecycle

For a game which ends after one step, the lifecycle might look a little something like this:

• :startup
  • :pre-step
    • :pre-stage
      • :update
    • :post-stage
    • :pre-stage
      • :render (user defined stage)
    • :post-stage
  • :post-step
• :tear-down

Reserved stages

#{:start-up :pre-step :pre-stage :update :post-stage :post-step :tear-down}