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Need some advice about creating game overlay in Linux (self.rust)

submitted 3 months ago by Commodore to c/[email protected]

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Hi. I've been learning Rust for a while, and I want to take on an actual project now to learn even more. I need to be pointed in the right direction for one aspect of the affair, and I hope someone here can help me.

I want to create a deck tracker for Hearthstone that runs natively in Linux. This is, on the back end, a fairly simple matter of parsing a constantly updated file that tracks everything that happens in the game. On the front end, however, I want to create a window that sits on top of the fullscreen Hearthstone window and shows me stuff. The "stuff" doesn't have to be images or anything fancy, I'll take whatever I can get, but I don't know how to get started on this part.

So the task is as follows: Create an overlay on top of the fullscreen Hearthstone client, preferably under Wayland, and update it constantly with new information about cards drawn, cards left in deck, that sort of thing.

How do I tackle this problem? Are there any crates that'll let me create such a window and render stuff to it? How would you approach the problem?

Thanks in advance.

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[–] [email protected] 7 points 3 months ago (1 children)

There's two main options to approach this: either you inject into the game like how MangoHUD does it, or you make an overlay window that your window manager/compositor helpfully places on top for you.

The second option is pretty simple as any GUI library will give you the window, you just need some help from the compositor side to do the rest. That part can also be pretty easy thanks to Wayland nesting: you can use whatever compositor you want for this, not just the one from your DE. Gamescope for example might work, if not wlroots+layer-shell.

You can also be your own nested compositor by using Smithay, which is in Rust and was made by System76 to be the library behind COSMIC's compositor. Looking at the examples, it looks not too crazy to use. Then you just run the game under yourself and you can do whatever you want.

Injecting into the game isn't too crazy either, you compile to a library and force load it with LD_PRELOAD and override some OpenGL/Vulkan functions that lets you add your own draw commands on top before the frame is finished.

I think avoiding injecting into the game is cleaner and easier as you're completely independent from the game client, so you won't crash the game and you can also just test out your code as a regular window, and restart it mid game. Injecting would also trigger anticheat if present. Which, what you're doing kind of is, even though anyone could also just pen and paper it.

[–] Commodore 2 points 3 months ago

Thanks so much for taking the time to write that long post. I have lots of things to dig into now. I think I'd prefer not injecting anything into the game for the reasons you mentioned, the most important consideration being the anticheat risk. I don't know what the company behind the game have implemented of that nature.