gallantzm said:
I'm aware big game studios tend to have custom-developed engines, and I was just wondering how they work, do they have a fully-fledged GUI where you can create worlds visually like in unity or are they more like all the boilerplate code necessary to build a game(like graphics rendering boilerplate, audio boilerplate, a basic game loop, and things like that)?
It depends on the game and the engine.
Most of they time they are a collection of tools. Tools are often built specifically for the game, the larger the game the more tools will be custom built for it.
Ultimately everything boils down to code and data. What you describe as “rendering boilerplate, audio boilerplate, a basic game loop” exist in every graphical game even if you don't see it. Just because you don't compile the code yourself like using Unity or stock Unreal doesn't mean it doesn't exist.
Exactly how each game loads and processes the systems and their data is unique to each game implementation and their tools. Today's modern game engines like Unreal and Unity work as a modular engine core which then loads the as a secondary library. The secondary library can be what you consider the main game, and can just as easily load an editor as a secondary library, load plugins as a secondary library, load or unload whatever else they want as modules. It is quite a powerful model, and it's gained popularity over the decades. It isn't just used in games, but across a wide range of software.
For tools, often there are several asset editors that vary based on the game. On older games they would do things like manage sprite libraries and allow artists and animators and designers to manipulate data outside the game. In some games they are tools to modify design-adjustable values, sometimes they connect to a running instance of the game so they be modified in live view, other times they edit configuration files like xml data which get loaded in the next run. In some games they are tools integrated into the main game to allow direct adjustment. Other times they are raw data like data table files which can be edited in Excel or other spreadsheet programs and saved back out as CSV or run through export scripts. There can be tools for manipulating story trees, tools for localization and translation, tools for map editing, tools for editing interactions, tools for editing probability curves, tools for editing transition graphs, tools for viewing and editing physics, tools for viewing and editing UI widgets, tools for viewing and editing model snap points, tools for viewing and editing animation curves, tools for viewing and editing terrain, tools for viewing or editing various flows of data, tools for whatever else might be imagined.
