Karl2D is a library for making 2D games using the Odin programming language. It focuses on making 2D gamedev fun, fast and beginner friendly. It also uses as few dependencies as possible. See karl2d.doc.odin for an API overview.

Support the project by becoming a sponsor here on GitHub or on Patreon.

"Hello world" program (draws the text "Hellope!" in a window):

package hello_world

import k2 "karl2d"

main :: proc() {
    k2.init(1280, 720, "Greetings from Karl2D!")

    for k2.update() {
        k2.clear(k2.LIGHT_BLUE)
        k2.draw_text("Hellope!", {50, 50}, 100, k2.DARK_BLUE)
        k2.present()
    }

    k2.shutdown()
}

See the examples folder for a wide variety of example programs.

Some examples are available as live web builds: hellope, basics, camera, box2d, fonts, gamepad, mouse, render_texture, snake.

Discuss and get help in the #karl2d channel on my Discord server.

Beta 2

Karl2D is currently in its SECOND BETA period. If you find any issues, then please create an issue here on GitHub!

Beta 2 has these features:

• Rendering of shapes, textures and text with automatic batching
• Support for shaders and cameras
• Windows support (D3D11 and OpenGL)
• Mac support (OpenGL)
• Linux support (OpenGL)
• Web support (WebGL, no emscripten needed!)
• Input: Mouse, keyboard, gamepad

Warning

Beta 2 does NOT have the following features, but they are planned in the order stated:

• Sound
• System for cross-compiling shaders between different backends (HLSL, GLSL, GLSL ES, MSL etc)
• Metal rendering backend for Mac (OpenGL already works)

When I've gotten through this list, then the library is close to 1.0

See the list of milestones to see the progress on each Beta version and what is included in each.

Warning

As this is a beta test version, changes to the API will happen.

I wrote a newsletter about the beta 2 release: https://news.zylinski.se/p/karl2d-beta-is-here

How to make a web build of your game

There's a build script located in the build_web folder. Run it like this:

odin run build_web -- your_game_path

The web build will end up in your_game_path/bin/web.

Note

You can run the build_web script from anywhere by doing: odin run path/to/karl2d/build_web -- your_game_path

Warning

On Linux / Mac you may need to install some lld package that contains the wasm-ld linker. It's included with Odin on Windows.

It requires that your game contains an init procedure and a step procedure. The init procedure is called once on startup and the step procedure will be called every frame of your game.

Also, see the minimal_hello_world_web.odin example.

The build_web tool will copy odin.js file from <odin>/core/sys/wasm/js/odin.js into the bin/web folder. It will also copy a HTML index file into that folder.

It will also create a build/web folder. That's the package it actually builds. It contains a bit of wrapper code that then calls the init and step functions of your game. The result of building the wrapper (and your game) is a main.wasm file that also ends up in bin/web.

Launch your game by opening bin/web/index.html in a browser.

Note

To get better in-browser debug symbols, you can add -debug when running the build_web script: odin run build_web -- your_game_path -debug Note that it comes after the --: That's the flags that get sent on to the build_web program! There are also -o:speed/size flags to turn on optimization.

Warning

If you open the index.html file and see nothing, then there might be an error about "cross site policy" stuff in the browser's console. In that case you can use python to run a local web-server and access the web build through it. Run python -m http.server in the bin/web folder and then navigate to https://localhost:8000.

Architecture notes

The platform-independent parts and the API lives in karl2d.odin.

karl2d.odin in turn has a window interface and a rendering backend.

The window interface depends on the operating system. I do not use anything like GLFW in order to abstract away window creation and event handling. Less libraries between you and the OS, less trouble when shipping!

The rendering backend tells Karl2D how to talk to the GPU. I currently support three rendering APIs: D3D11, OpenGL and WebGL. On some platforms you have multiple choices, for example on Windows you can use both D3D11 and OpenGL.

The platform independent code in karl2d.odin creates a list of vertices for each batch it needs to render. That's done independently of the rendering backend. The backend is just fed that list, along with information about what shader and such to use.

The web builds do not need emscripten, instead I've written a WebGL backend and make use of the official Odin JS runtime. This makes building for the web easier and less error-prone.

Troubleshooting

Linux build error: libudev is missing

Try installing a package such as systemd-devel or systemd-dev.

Contributing and Pull Request rules

Are you interested in helping with Karl2D development? Thank you! You can look at open issues here on GitHub. You get your contributions into the project using a Pull Request.

You can always open a draft Pull Request and work on your stuff in there. There are no rules for draft pull requests. When you want to turn your draft into a ready-for-review Pull Request, then please follow this rule checklist: https://github.com/karl-zylinski/karl2d/blob/master/.github/pull_request_template.md

Have fun!

Logo by chris_php.