Odin + Raylib + Hot Reload template

This is an Odin + Raylib game template with Hot Reloading pre-setup. It makes it possible to reload gameplay code while the game is running.

Supported platforms: Windows, macOS, Linux and web.

Supported editors and debuggers: Sublime Text, VS Code and RAD Debugger.

See The Legend of Tuna repository for an example project that also uses Box2D: https://github.com/karl-zylinski/the-legend-of-tuna

I used this kind of hot reloading while developing my game CAT & ONION.

Hot reload quick start

Note

These instructions use some Windows terminology. If you are on mac / linux, then replace these words:

• bat -> sh
• exe -> bin
• dll -> dylib (mac), so (linux)

1. Run build_hot_reload.bat to create game_hot_reload.exe and game.dll (located in build/hot_reload). Note: It expects odin compiler to be part of your PATH environment variable.
2. Run game_hot_reload.exe, leave it running.
3. Make changes to the gameplay code in source/game.odin. For example, change the line rl.ClearBackground(rl.BLACK) so that it instead uses rl.BLUE. Save the file.
4. Run build_hot_reload.bat, it will recompile game.dll.
5. The running game_hot_reload.exe will see that game.dll changed and reload it. But it will use the same Game_Memory (a struct defined in source/game.odin) as before. This will make the game use your new code without having to restart.

Note, in step 4: build_hot_reload.bat does not rebuild game_hot_reload.exe. It checks if game_hot_reload.exe is already running. If it is, then it skips compiling it.

Release builds

Run build_release.bat to create a release build in build/release. That exe does not have the hot reloading stuff, since you probably do not want that in the released version of your game. This means that the release version does not use game.dll, instead it imports the source folder as a normal Odin package.

build_debug.bat is like build_release.bat but makes a debuggable executable, in case you need to debug your non-hot-reload-exe.

Web build

build_web.bat builds a release web executable (no hot reloading!).

Web build requirements

• Emscripten. Download and install somewhere on your computer. Follow the instructions here: https://emscripten.org/docs/getting_started/downloads.html (follow the stuff under "Installation instructions using the emsdk (recommended)").
• Recent Odin compiler: This uses Raylib binding changes that were done on January 1, 2025.

Web build quick start

1. Change EMSCRIPTEN_SDK_DIR in build_web.bat/sh to point to your emscripten setup.
2. Run build_web.bat/sh.
3. Web game is in the build/web folder.

Note

You may not be able to start build/web/index.html directly, because you'll get "CORS policy" javascript errors. You can get around that by starting a local web server using python. Go into build/web and run:

python -m http.server

Open localhost:8000 in your browser to play the game.

If you don't have python, then emscripten actually comes with it. Look in the python folder of where you installed emscripten.

See https://github.com/karl-zylinski/odin-raylib-web for more info on how the web build works.

See https://github.com/karl-zylinski/the-legend-of-tuna for a gamejam game I made using this template. It supports web builds. In fact, the web build support is ported backwards from that game into this template and the odin-raylib-web repository I mentioned just above.

Warning

The web build relies on emscripten, because raylib requires emscripten in order to work on the web. This comes with some limitations for our Odin code. We can only compile in "freestanding mode", which means we have no operating system support at all. For example, no allocators are automatically set up for us. Therefore I have made sure to setup web-compatible allocators and a logger. This is done by interfacing with the libc stuff that emscripten exposes. This also means that some parts of core do not work.

If you need to use os.read_entire_file on the web, then have a look at the source/os package. It implements read_entire_file and write_entire_file using emscripten libc. Let me know if you need any other OS procs to port your game to the web!

Assets

You can put assets such as textures, sounds and music in the assets folder. That folder will be copied when a release build is created and also integrated into the web build.

The hot reload build doesn't do any copying, because the hot reload executable lives in the root of the repository, alongside the assets folder.

Sublime Text

For those who use Sublime Text there's a project file: project.sublime-project.

How to use:

• Open the project file in sublime
• Choose the build system Main Menu -> Tools -> Build System -> Odin + Raylib + Hot Reload template (you can rename the build system by editing project.sublime-project manually)
• Compile and run by pressing using F7 / Ctrl + B / Cmd + B
• After you make code changes and want to hot reload, just hit F7 / Ctrl + B / Cmd + B again

RAD Debugger

You can hot reload while attached to RAD Debugger. Attach to your game_hot_reload executable, make code changes in your code editor and re-run the the build_hot_reload script to build and hot reload.

VS Code

You can build, debug and hot reload from within VS Code. Open the template using File -> Open Folder....

Requirements for debugging to work:

• Windows: C++ build tools
• Linux / Mac: CodeLLDB

Launch with Run Hot Reload launch task, see image above. After you make code changes press Ctrl + Shift + B to rebuild and hot reload.

Windows Debugging hacks

On Windows the degugging while hot reloading works by outputting a new PDB each time the game DLL is built. It cleans up the PDBs when you do a fresh start. See build_hot_reload.bat for details.

Demo streams

Streams that start from this template:

• 48 hour "Odin Holiday Gamejam": https://www.youtube.com/playlist?list=PLxE7SoPYTef2XC-ObA811vIefj02uSGnB Every minute of the development is documented. The resulting game of the gamejam is here: https://zylinski.itch.io/the-legend-of-tuna
• CAR RACER prototype: https://www.youtube.com/watch?v=KVbHJ_CLdkA
• "point & click" prototype: https://www.youtube.com/watch?v=iRvs1Xr1W6o
• Metroidvania / platform prototype: https://www.youtube.com/watch?v=kIxEMchPc3Y
• Top-down adventure prototype: https://www.youtube.com/watch?v=cl8EOjOaoXc

Atlas builder

The template works nicely together with my atlas builder. The atlas builder can build an atlas texture from a folder of png or aseprite files. Using an atlas can drastically reduce the number of draw calls your game uses. There's an example in that repository on how to set it up. The atlas generation step can easily be integrated into the build bat / sh files such as build_hot_reload.bat

Questions?

Ask questions in my gamedev Discord: https://discord.gg/4FsHgtBmFK

I have a blog post about Hot Reloading here: http://zylinski.se/posts/hot-reload-gameplay-code/

Have a nice day! /Karl Zylinski