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83 lines
2.6 KiB
Markdown
83 lines
2.6 KiB
Markdown
# Jojo #
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Jojo is an Entity Component System for lua that's simple, flexible, and useful.
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Because of lua's tabular nature, Entity Component Systems are a natural choice
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for simulating large and complex systems. For more explanation on Entity
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Component Systems, here is some
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[basic info](http://en.wikipedia.org/wiki/Entity_component_system "Wikipedia").
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## Use It ##
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Copy paste jojo.lua into your source folder.
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## Overview ##
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Jojo has four important types: Worlds, Aspects, Systems, and Entities.
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Entities, however, can be any lua table.
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### Entities ###
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Entities are simply lua tables of data that gets processed by Systems. Entities
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should contain primarily data rather that code, as it is the Systems's job to
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do logic on data. Henceforth, a key-value pair in an Entity will
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be referred to as a Component.
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### Worlds ###
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Worlds are the outermost containers in Jojo that contain both Systems
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and Entities. In typical use, only one World is used at a time.
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### Systems ###
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Systems in Jojo describe how to update Entities. Systems select certain Entities
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using an aspect, and then only update those select Entities. Systems have three
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parts: a one-time update function, a per Entity update function, and an Aspect.
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The one-time update function is called once per World update, and the per Entity
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update function is called once per Entity per World update. The Aspect is used
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to select which Entities the System will update.
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### Aspects ###
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Aspects are used to select Entities by the presence or absence of specific
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Components. If an Entity contains all Components required by an Aspect, and
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doesn't contain Components that are excluded by the Aspect, it is said to match
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the Aspect. Aspects can also be composed into more complicated Aspects that
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are equivalent to the union of all sub-Aspects.
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## Example ##
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```lua
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local jojo = require("jojo")
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local World = jojo.World
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local Aspect = jojo.Aspect
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local System = jojo.System
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local personAspect = Aspect({"name", "mass", "phrase"})
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local talkingSystem = System(
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function (delta)
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print("Talking system has started.")
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end,
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function (p, delta)
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print(p.name .. ", who weighs " .. p.mass .. "pounds, says, " .. p.phrase)
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end,
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personAspect
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)
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local world = World(talkingSystem)
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local joe = {
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name = "Joe",
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phrase = "I'm a plumber.",
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mass = 150,
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hairColor = "brown"
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}
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world:add(joe)
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world:update(1)
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```
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## Testing ##
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To test Jojo, simply clone the project, cd into the project directory, and
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run `lua jojotest.lua` from command line.
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## TODO ##
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* Dynamically add and remove systems
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* More testing
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* Performance testing / optimization
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* API outside of source code
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