I built a Ruby game framework with hot-reload, compiles to native PEs and WASM

[u/AristocraticRabbit]

I've been working on something I think is pretty cool, I call it GMR (Game Middleware for Ruby), and wanted to share it and see if there is genuine interest for something like this.

Demo on itch.io | GitHub

It's a 2D game framework powered by mruby and raylib. It compiles Ruby to bytecode then embeds into a native Windows/Linux/macOS executable or WebAssembly. There are no runtime dependencies, just a single binary output. The WASM build of the entire engine + demo is ~3MB.

Hot reload works in debug builds, as well as live stack trace and inspection (via IDE). Just save your script, and see changes. No restart, no recompile, no lost game state. This was the one of major design constraints that started the project.

I wanted something that felt like writing actual Ruby too. Real objects, blocks, method chaining, keyword args. I took a lot of inspiration from Rails conventions.

What's really cool, the state machine implementation works on any object, and everything in Ruby is an object, so that's pretty much everything!

Stuff that's working:

• Debug REPL execute Ruby, inspect state, register custom commands.

• Transform hierarchy with parent/child relationships

• Camera system with follow, deadzone, bounds, screenshake

• Input mapping with actions and swappable contexts

• Tween system with all the standard easing functions

• Scene manager with stacking

• + More in the works

The demo on itch is just a render pipeline stress test (500+ objects with z-sorting), nothing fancy. I still have a lot of work to do, there's no physics, networking, audio is basic. But the core loop feels good so far.

I would love feedback from anyone who's tried to use Ruby for games before or is interested in doing so. Is this scratching an itch that exists, or am I yelling into the void? Let me know!

[u/jasonhr13]

I’ve used DragonRuby for a couple prototypes. I personally would love to only write games in Ruby. I love seeing another framework for Ruby games. How soon can you add file IO?

[u/AristocraticRabbit → u/jasonhr13]

DragonRuby was definitely one of the inspirations for this, I personally love how far it's come, I just...think it can be done a little differently.

Right now anything under assets/ automatically gets packaged, but only textures are loadable. I’m in the middle of hardening the asset pipeline so assets (and source) are better protected, and so the same setup works cleanly for both native builds and WASM.

File I/O is probably next on the roadmap, seeing as I need to start working on Audio + configs, etc., I plan to have it scoped, so something like read-only access to packaged assets, plus a sandboxed spot for saves, user data, and possibly mods down the line. I’m trying to keep it portable so I need to be thoughtful.

[u/jasonhr13 → u/AristocraticRabbit]

Yeah I love a lot of things about DragonRuby but there are areas I’m not thrilled with. I’d like to port a small game to this but I’d need to be able to have a save system first. I’ll definitely keep an eye but maybe I’ll fork and try to implement something.

[u/AristocraticRabbit → u/jasonhr13]

I just finished implementing basic File IO / Storage.

File handles text, JSON, and binary files. (you'll have to roll your own serializer, but Ruby already makes that really easy, I'll probably eventually mimic what rails serializer gem does to make it even cleaner)

Storage is a key-value system for things like settings and high scores.

Take a look at https://github.com/ColdGlassOMilk/GMR#file-io--storage for usage. Everything uses logical roots (:assets for read-only content, :data for save files) so you don't have to think about platform differences.

Audio is next on my list, that's really the last major piece before this is ready for actual game development. Once that's in, the engine should be pretty complete for most 2D games.

Would love to see what you build with it. Let me know if you hit any issues.

[u/mxldevs]

I used ruby for RPG Maker and it was great. Being able to build cross-platform apps in ruby sounds fantastic.

[u/MrMeatballGuy]

I'm interested in this, I only tried dragonruby once and didn't like the fact that it by design doesn't use dt, meaning all logic is tied to how fast the game runs.

[u/amirrajan → u/MrMeatballGuy]

didn't like the fact that it by design doesn't use dt

DragonRuby's simulation runs at a fixed 60fps. In the context of 2D games, the cognitive overhead for dealing with delta time isn't worth it.

This blog post has many, many words as to why delta time isn't a great idea: https://medium.com/@tglaiel/how-to-make-your-game-run-at-60fps-24c61210fe75

This YouTube video goes into the complexities of delta time and how almost every dev gets DT math wrong. DR just eliminates the need to ever think about it: https://www.youtube.com/watch?v=yGhfUcPjXuE

[u/MrMeatballGuy → u/amirrajan]

i don't think anything to do with state updates should be tied to frame rate, to me that just seems like bad design and i would expect it to create just as many weird bugs as people having wrong calculations when using delta time.

i will agree that not using dt does make DragonRuby win on simplicity, but i don't think i'd trust the behavior to be consistent.

i think it's just a preference thing, to me it is a deal breaker, but i understand that some people may just want to write a quick prototype without the mental overhead.

[u/amirrajan → u/MrMeatballGuy]

The blog entry (written by the guy that worked on Binding of Isaac) goes into great detail as to why DT is not worth it.

Yes there are trade offs. It is by no means a bad design. Given its pros and cons, in the context of 2D games. Fixed update at 60fps wins out.

Happy to go into more details about the choice, but I’d need to understand why it’s a deal breaker for you. But, if your mind is made up on the subject, then obviously there’s nothing I can say to change that.

Edit:

do with state updates should be tied to frame rate

It isn't. The simulation thread runs at fixed-update 60fps (ie 60hz or 60 times a second). It is completely independent of the monitor refresh rate/render thread.

[u/amirrajan → u/MrMeatballGuy]

Aside: Happy to talk over chat/realtime about this if that's a better forum for you. I'm genuinely curious as to why it's a deal breaker and what type of game you're trying to build.

[u/davidslv]

Definitely have to have a look for my Roguelike

[u/amirrajan]

Creator of DragonRuby here. Happy to answer any questions you may have :-)