Jojo

Jojo is an Entity Component System for lua that's simple, flexible, and useful. Because of lua's tabular nature, Entity Component Systems are a natural choice for simulating large and complex systems. For more explanation on Entity Component Systems, here is some basic info.

Use It

Copy paste jojo.lua into your source folder.

Overview

Jojo has four important types: Worlds, Aspects, Systems, and Entities. Entities, however, can be any lua table.

Entities

Entities are simply lua tables of data that gets processed by Systems. Entities should contain primarily data rather that code, as it is the Systems's job to do logic on data. Henceforth, a key-value pair in an Entity will be referred to as a Component.

Worlds

Worlds are the outermost containers in Jojo that contain both Systems and Entities. In typical use, only one World is used at a time.

Systems

Systems in Jojo describe how to update Entities. Systems select certain Entities using an aspect, and then only update those select Entities. Systems have three parts: a one-time update function, a per Entity update function, and an Aspect. The one-time update function is called once per World update, and the per Entity update function is called once per Entity per World update. The Aspect is used to select which Entities the System will update.

Aspects

Aspects are used to select Entities by the presence or absence of specific Components. If an Entity contains all Components required by an Aspect, and doesn't contain Components that are excluded by the Aspect, it is said to match the Aspect. Aspects can also be composed into more complicated Aspects that are equivalent to the union of all sub-Aspects.

Example

local jojo = require("jojo")

local World = jojo.World
local Aspect = jojo.Aspect
local System = jojo.System

local personAspect = Aspect({"name", "mass", "phrase"})
local talkingSystem = System(
    nil,
    function (p, delta)
        p.mass = p.mass + delta * 3
        print(p.name .. ", who weighs " .. p.mass .. " pounds, says, \"" .. p.phrase .. "\"")
    end,
    personAspect
)

local world = World(talkingSystem)

local joe = {
    name = "Joe",
    phrase = "I'm a plumber.",
    mass = 150,
    hairColor = "brown"
}

world:add(joe)

for i = 1, 20 do
    world:update(1)
end

Testing

To test Jojo, simply clone the project, cd into the project directory, and run lua jojotest.lua from command line.

TODO

• Dynamic reordering of Systems
• More testing
• Performance testing / optimization
• API outside of source code