File System
Filesystem usage is yet another hot topic in engine development. This means, where are assets stored, how are they accessed, how do multiple programmers edit the same repository, etc.
Initial versions of the engine (and previous iterations before it was named Godot) used a database. Assets were stored there and assigned an ID. Other approaches were tested, too, with local databases, files with metadata, etc. To say truth, and after a long time, simplicity proved to be best and Godot stores all assets as files in the flesystem.
Godot stores resources to disk. Anything, from a script, to a scene or a PNG image is a resource to the engine. If a resource contains properties that referece other resources on disk, the path to that resource is included. If it has sub-resources that are built-in, the resource is saved in a single file together with all the bundled sub-resources. For example, a font resource is often saved with the character textures bundled inside.
Metadata files were also dropped and the whole engine design tries to avoid them. The reason for this is simple, existing asset managers and VCSs are just much better than anything we can implement, so Godot tries the best to play along with SVN, Git, Mercurial, Perforce, etc.
The mere existence of this file marks that there is a Godot project in that directory and all sub-directories. This file contains the project configuration in plain text, win.ini style, though it will work to mark the existence of a project even if the file is empty.
Example of a filesystem:
/engine.cfg
/enemy/enemy.scn
/enemy/enemy.gd
/enemy/enemysprite.png
/player/player.gd
Godot only supports "/" as a directory delimiter. This is done for portability reasons. All operating systems support this, even Windows, so a path such as c:\project\engine.cfg needs to be typed as c:/project/engine.cfg.
For accessing resources, using the host OS filesystem layout can be cumbersome and non portable. To solve this problem, the specal path %%"res://"%% was created.
The path "res://" will always point at the project root (where engine.cfg is located, so in fact "res://engine.cfg" is always valid).
This filesystem is read-write only when running the project locally from the editor. When exported or when running on different devices (such as phones or consoles, or running from DVD), the filesystem will become read-only and writing will no longer be permitted.
Writing to disk is still needed often, from doing a savegame to downloading content packs. For this, the engine ensures that there is a special path %%"user://"%% that is always writable.
Of course, opening the host filesystem always works, as this is always useful when Godot is used to write tools, but for shipped projects this is discouraged and may not even be supported in some platforms.
Not everything is rosy. Using resources and files and the plain filesystem has two main drawbacks. The first is that moving assets around (renaming them or moving them from a directory to another inside the project) once they are referenced is not that easy. If this is done, then dependencies will need to be re-satisfied upon load.
The second is that under Windows or OSX, file access is case insensitive. If a developer works in this operating system and saves a file like "myfile.PNG", then references it as "myfile.png", it will work there, but not on any other platform, such as Linux, Android, etc. It may also not work on exported binaries, which use a compressed package for files.
Because of this, please instruct your team to use a specific naming convention for files when working with Godot!