I don't really know what to expect. You want to see good production code, and the FOSS community is way way WAY better at this than some of the bubble gum you'd see in a professional setting.
Your question is too general, so I can't exactly give you a specific repository. I could direct you to BGFX[1] for a decent architecture of a cross platform renderer, but if you're not a graphics programmer, that may be a bad exercise, as you'd spend more time learning jargon than studying clean code. Or it uses patterns (or lack of, given graphics programming) that don't apply to your domain.
Gitlab, Bitbucket.
I don't really know what to expect. You want to see good production code, and the FOSS community is way way WAY better at this than some of the bubble gum you'd see in a professional setting.
Your question is too general, so I can't exactly give you a specific repository. I could direct you to BGFX[1] for a decent architecture of a cross platform renderer, but if you're not a graphics programmer, that may be a bad exercise, as you'd spend more time learning jargon than studying clean code. Or it uses patterns (or lack of, given graphics programming) that don't apply to your domain.
[1]: https://github.com/bkaradzic/bgfx