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<title>Exmods | Modding ECS</title> |
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<h3><a href="index.html" title="You know your browser has a back button, right?">Back to list</a></h3> |
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<h1>Modding ECS in Gamecraft</h1> |
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<div class="text-content"> |
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<p> |
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<span class="tab"></span> |
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Gamecraft is built on an entity component system created by FreeJam's CTO called <a href="https://github.com/sebas77/Svelto.ECS">Svelto.ECS</a>, which is a quite powerful piece of open-source software. |
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The ECS paradigm is a relatively novel programming concept, but many frameworks exist including one made by the Unity Engine devs specifically for their engine called <a href="https://connect.unity.com/p/what-is-unity-ecs">UECS</a>. |
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ECS is a data-oriented system which uses "entities" instead of "objects" from object-oriented programming. |
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An entity is comprised of independent components which act like individual properties for an object in OOP. |
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All of the components are stored in some sort of fast in-memory database (Svelto.ECS uses a Dictionary). |
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What makes ECS great is that it's fast, |
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since the computer only needs to worry about the component in cache instead of the entire object, |
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and it makes the code easier to maintain, |
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since you can add a new component to an existing entity without touching other components in the same entity. |
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</p> |
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<p> |
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<span class="tab"></span> |
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ECS is great, but it can be a lot to wrap your head around. |
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I've found that the best way to understand it is to jump in, swear at your computer a bit, and slowly accept it for what it is. |
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A lot of material I've seen says that ECS is really only practical for games, |
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but the idea of data-oriented design is a universal concept. |
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Data-oriented programs are the future, since big data and machine learning are focused on number-crunching. |
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So if you need a reason to persevere through your ECS learning, think of that. |
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Unfortunately, ECS is unlikely to be the way to get there, but it is the way to make a (good) modern game. |
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And Gamecraft is one of those modern good games... well at least it uses ECS. |
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</p> |
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<p> |
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<span class="tab"></span> |
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Gamecraft is FreeJam's first completely ECS-based game. |
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Robocraft and CardLife both used Svelto.ECS as well, but the game logic wasn't completely reliant on it. |
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Because all of Gamecraft's data is handled by Svelto.ECS, |
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it's easier to mod than CardLife and Robocraft (or so I'd imagine, I've never tried). |
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The biggest hurdle is to get access to the database containing all of the entity components. |
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Luckily, Svelto.ECS will automatically provide that database to engines, the logic and behaviour implementors in Svelto.ECS. |
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In Gamecraft, engines are usually registered during the "compose" stage, which occurs in loading screens or when switching gamemode. |
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I think of the compose stage as when the composer taps his baton on the stand in front of him, |
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right after the musicians have walked on stage and sat down (init stage) and right before the music starts playing (gameplay stage). |
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Registering an engine to Svelto.ECS is made quite trivial by <a href="https://harmony.pardeike.net/">Harmony</a>, |
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which can intercept a method call and its parameters to allow you to perform your own operations. |
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Specifically, all of the compose methods in Gamecraft get passed a Svelto.ECS EngineRoots object, |
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which is how Gamecraft (and now me) registers engines to operate on entity components. |
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</p> |
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<p> |
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<span class="tab"></span> |
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In the interest of not going sued for reverse-engineering Gamecraft or divulging company secrets I won't go into much more detail |
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(although they're not very good company secrets if me, |
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a person living on a different continent, |
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working for a different company, |
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figured out their secrets in my spare time). |
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You can find out more details about Gamecraft by using a |
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<a href="https://github.com/0xd4d/dnSpy#dnspy---latest-release---%EF%B8%8F-donate">C# decompiler</a> to view the original code, |
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no reverse-engineering required. |
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By the way, <a href="https://en.wikipedia.org/wiki/Reverse_engineering#Legality">reverse-engineering</a> is |
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<a href="https://ghbintellect.com/is-reverse-engineering-legal/">usually legal</a> anyway. |
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Of course, I'm not a lawyer, and I don't like closed-source software that much so I'm a bit biased. |
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Interestingly, the European laws about |
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<a href="https://en.wikipedia.org/wiki/Computer_Programs_Directive">software protection</a> |
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seem to explicitly allow external mods and servers (you can tell I'm still a bit annoyed about RC14 getting shutdown). |
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Regardless, FreeJam seems to be ok with the unofficial Gamecraft mods that have been created so far, |
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so I wouldn't expect them to suddenly change their stance on mods in the near future. |
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</p> |
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<p> |
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<span class="tab"></span> |
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The <a href="https://git.exmods.org/modtainers/GamecraftModdingAPI#user-content-gamecraftmoddingapi">GamecraftModdingAPI</a> |
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is probably the best example of modding with ECS. |
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It provides a friendly object-oriented API for developers who want simplicity. |
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For developers who want performance or understand the ECS paradigm, the modding API offers an easy way to register engines, |
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so that Harmony isn't even required in the process of getting the entities database for modding entity components. |
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As a major contributor to the GamecraftModdingAPI, I've seen how ECS has simplified modding. |
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One of Svelto.ECS's primary focuses is code maintainability, which is very obvious whenever Gamecraft is updated. |
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The average Gamecraft update breaks one or two parts of the API, |
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and that's usually only caused by one or two variables changing name or location. |
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I'd bet that if half of Gamecraft were rewritten, |
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the biggest fix that the GamecraftModdingAPI would need would be changing the name of the components the API queries. |
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The focus on maintainability doesn't just make Gamecraft easier to develop, it also makes mods easier. |
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</p> |
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<p> |
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<span class="tab"></span> |
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The data-oriented design of ECS helps as well. |
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The object-oriented API in the GamecraftModdingAPI still queries entity components behind-the-scenes, |
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so even OOP can take advantage of ECS design, albeit with some drawbacks. |
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The database system in Svelto.ECS purposely allows for new entities to created but not made accessible immediately for some deterministic reason. |
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In the event that a new entity is created as an object through the object-oriented API, |
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the GamecraftModdingAPI has to force the database to sync new entities before any of the object's properties can be accessed. |
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This database sync operation is a lot of unnecessary overhead which could be avoided with pure ECS. |
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Pure ECS modding is easy, |
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since almost every operation can be accomplished by operating on one or more entity components in the entity database. |
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In Gamecraft's case, there's never more than one entity database on the go at once, |
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which makes modding easy with a single point of contact. |
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Once you've got the active entities database, you've basically completely pwned Gamecraft. |
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</p> |
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<p> |
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<span class="tab"></span> |
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A year ago, I thought ECS was a fancy niche concept which would be worthless for me to learn. It may still be worthless for my job, but its a vital part of Gamecraft and mods that I wouldn't pass up. I wonder when FreeJam will give us an official modding API for interacting with Svelto.ECS... |
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