SDK for in-game overlays

Question

What little information I managed to dig out on developing in-game overlays (similar to what Steam does) mentions having to intercept calls graphics API's frame swapping function, and hook my own drawing routine in it.

This appears to be what Mumble (a gaming VoIP) is doing. Since I've never done anything that involves hooking, and since I don't really have much experience with DirectX, I'm wondering if there is some sort of SDK, or even just a more readable example than Mumble that also implements input, that demonstrates how to implement an interactive in-game overlay. Mumble is great, but I don't seem to be able to wrap my head around it, especially around the more interesting things it does in order to hook its stuff properly.

Also, if you have more detailed info on how to do this on Mac and Linux... :-)

Answer 1

• Start by designing your overlay without intercepting graphics API. Keep in mind that the key input must use global hooks.
• Integrate it to the application using a Direct3D interceptor dll. Google it to retrieve a base code.

Edit:

• DirectX: Intercept Calls to DirectX with a Proxy DLL will give you downloadable source code.
• OpenGL: Chromium might be a good start.

Answer 2

Maybe GLIntercept could give you some inspiration. It provides an openGL.dll file that you put in your app's folder. Windows loads this dll instead of system32's one because of priority rules. GLIntercept forwards all calls to the system32's dll, but logs them all meanwhile. So, you could implement your own glSwapBuffers() which renders some more things, and then forwards the call.

Source code is available as well.

I upvote your question, and I'm interested in you future discoveries... feel free to repost when you have more info :)