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https://github.com/damn/gdl

Functional 2D game engine in clojure
https://github.com/damn/gdl

clojure game-engine gamedev

Last synced: 8 days ago
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Functional 2D game engine in clojure

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README 

        
# Archived: Development continues in https://github.com/damn/Fullmoon





  




# What is GDL?



The __vision__ of GDL is to be a __Game Development Language__ and make it _utterly simple_ to write games!



GDL is a functional 2D game engine built around the idea of a __context__ object which holds the current state of the application.



As you can see in the hello-world example below we call `create-context` once on app start and then it gets passed every frame to the `render` function.



The context object is is a clojure record ([gdl.context.Context](https://github.com/damn/gdl/blob/main/src/gdl/context.clj#L3)) which implements certain protocols, as defined in [gdl.context](https://damn.github.io/gdl/gdl.context.html). 



The current context is stored in an `atom` in [`gdl.app/current-context`](https://github.com/damn/gdl/blob/main/src/gdl/app.clj#L4). 

It is not suggested to access the state other than for debugging. It is __only__ used by UI callbacks, for changing the screen and passed to the application `render`.



GDL is basically a clojure API over the 2D parts of of [libgdx](https://libgdx.com/), as GDL evolved as an engine for [Cyber Dungeon Quest](https://github.com/damn/Cyber-Dungeon-Quest), an action RPG project. 

But you can easily extend the API for more libgdx features. 



You have full access to all libgdx under the hood and can do direct java interop anytime or acccess the OpenGL context, etc.



__Libgdx__ supports android and ios too, but I have not used those backends yet.



## [Context API](https://damn.github.io/gdl/gdl.context.html)



The following things can be all called on the `context` object.



* 📺 Change screens (different separate applications 'screens' like main-menu, options-menu, etc )

* 🌎 Having a GUI-view and a World-view (with a `world-unit-scale`, which means you can draw and reason about your game world at world-coordinates and not pixel-coordinates)

* 🎆Load and draw images

* 📐Drawing geometric shapes

* 🔈Playing sounds

* 🎮Checking for Mouse/Key input

* ☑️[Scene graph](https://libgdx.com/wiki/graphics/2d/scene2d/scene2d) for UI widgets using [vis-ui](https://github.com/kotcrab/vis-ui)

* 🔤Loading truetype fonts & drawing text

* 🗺️Loading [tiled](https://www.mapeditor.org/) `.tmx` maps and drawing them with lights&shadows in `world-unit-scale`

* 🖱️ Loading/setting cursors



# Hello World



You can run the hello world example in this repository with:



```

lein run -m gdl.hello-world

```



[https://github.com/damn/gdl/blob/f34a451e559363a1876e9d386516108333bdc5ce/test/gdl/hello_world.clj#L1-L25](https://github.com/damn/gdl/blob/429682e1af5196b2eee551f426eba95347171d55/test/gdl/hello_world.clj#L1-L22)



# On Mac



You need to set this environment variable:



```

export JVM_OPTS=-XstartOnFirstThread

```



# Updating the context



At the moment `render` does not return a new context object, as I am using `atom`s for my entities and state in the RPG project. 

This proved to be quite useful and I am not sure it is possible to remove those `atom`s as they are used as references and save the lookup by entity `:id`.



TODO: Still it might be useful for smaller projects to be able to just return a new `context` at the end of `render`.



# Extending the `Context` for your game



In [Cyber Dungeon Quest](https://github.com/damn/Cyber-Dungeon-Quest) I have defined more [game-specific context protocols](https://github.com/damn/Cyber-Dungeon-Quest/blob/master/src/cdq/context.clj). 



There is an example in [context.mouseover-entity](https://github.com/damn/Cyber-Dungeon-Quest/blob/master/src/context/mouseover_entity.clj) how to extend the context with your own protocols. 



Basically you call `extend-type gdl.context.Context` with your protocols and merge the necessary context-data at app start with the existing default-context.



By using namespaced keywords like `:context/mouseover-entity` and clojure's map destructuring it becomes quite __simple&easy__ to manage all the data in one object.



# Installation



[![](https://jitpack.io/v/damn/gdl.svg)](https://jitpack.io/#damn/gdl)



Add the following to your project.clj file:



```clojure

:repositories [["jitpack" "https://jitpack.io"]]



:dependencies [[com.github.damn/gdl "main-SNAPSHOT"]]

```



__Note: the jitpack for `main-SNAPSHOT` seems not to be working at the moment, use the latest commit hash!__



# [API Documentation](https://damn.github.io/gdl/)



# Games made with GDL



* [Cyber Dungeon Quest](https://github.com/damn/Cyber-Dungeon-Quest)