I've worked on several. You haven't heard of them because none of them shipped due to issues with commercial engines (in particular Unreal Engine 4).
They are very difficult to use if the game play semantics are complicated and require lots of interaction with world state or world geometry. If you're making a common FPS, they are great.
> They are very difficult to use if the game play semantics are complicated and require lots of interaction with world state or world geometry.
Could you give an example? I’m trying to understand what the limits look like. It appears to be trivial to you, but for someone outside of game design, I can’t imagine what those might be.
We almost never hit technical limits in the renderer, streaming systems, etc. Instead, we found that pushing gameplay systems beyond the prototype stage would require more and more effort, as we'd encounter deep engine bugs, or the tooling simply did not cater to our use case.
We ended up implementing more and more tooling outside the engine, and there comes a point where UE4 became a IO/Rendering system. We'd've been happier if the engine were modular in design from the get-go.
> we found that pushing gameplay systems beyond the prototype stage would require more and more effort
I understand that you're saying that some systems exist that can't work. I'm trying to understand what those systems would look like, and how the user would see it as being different. Do you have an example of the system/mechanic that can't work?
> Could you give an examples of a game that used a custom game engines that couldn’t achieve what they wanted in Unreal or Unity?
A game that doesn't require a multi-gigabyte download and a top-tier GPU and CPU to render stuff in 2D? ;)
There are many reasons people might want to opt out of existing game engines: full control over rendering pipelines, assets and dev. experience might be some of them.
Sure, but what does that mean, to the actual end product? Do you have any examples? I’m not a game dev, so to me, I would naively assume that these wouldn’t be limiting, or laughable, as the original comment suggested.
jai's author, Jonathan Blow, always creates a game from scratch. His games: Braid (highest rated XBox Live title when released, "Xbox Live Arcade Game of the Year", https://www.youtube.com/watch?v=YgGeBOC0PX4) and Witness (while not winning significant awards, regularly appears in Best of Decade games lists, https://www.youtube.com/watch?v=URjb3RBIe7c).
Besides that there are multiple games where people use their own engines:
In general, once you know what you're doing it sometimes pays to develop your own engine that is specific to what you're doing. Unity and Unreal are generalist enines that you still to bend to your will to do what you need to do and may have opinionated setups of things that are hard to work around, or maybe are omitted from the engine, or just plain don't allow you to do.
Edit: The only style I would think would be infinite/strange geometry, like Manifold garden (great game!). But, it’s Unity.