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 quake 3 filesystem

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PostSubject: quake 3 filesystem   Sun Mar 04, 2012 1:30 pm

if you've ever wondered about all the crazy tremulous directories and .pk3 packages,
this is a very nice *manual* that i found inside the src on the filesystem:


All of Quake's data access is through a hierarchical file system, but the contents of
the file system can be transparently merged from several sources.

A "qpath" is a reference to game file data. MAX_ZPATH is 256 characters, which must include
a terminating zero. "..", "", and ":" are explicitly illegal in qpaths to prevent any
references outside the quake directory system.

The "base path" is the path to the directory holding all the game directories and usually
the executable. It defaults to ".", but can be overridden with a "+set fs_basepath c:\quake3"
command line to allow code debugging in a different directory. Basepath cannot
be modified at all after startup. Any files that are created (demos, screenshots,
etc) will be created reletive to the base path, so base path should usually be writable.

The "cd path" is the path to an alternate hierarchy that will be searched if a file
is not located in the base path. A user can do a partial install that copies some
data to a base path created on their hard drive and leave the rest on the cd. Files
are never writen to the cd path. It defaults to a value set by the installer, like
"e:\quake3", but it can be overridden with "+set fs_cdpath g:\quake3".

If a user runs the game directly from a CD, the base path would be on the CD. This
should still function correctly, but all file writes will fail (harmlessly).

The "home path" is the path used for all write access. On win32 systems we have "base path"
== "home path", but on *nix systems the base installation is usually readonly, and
"home path" points to ~/.q3a or similar

The user can also install custom mods and content in "home path", so it should be searched
along with "home path" and "cd path" for game content.

The "base game" is the directory under the paths where data comes from by default, and
can be "base".

The "current game" may be the same as the base game, or it may be the name of another
directory under the paths that should be searched for files before looking in the base game.
This is the basis for addons.

Clients automatically set the game directory after receiving a gamestate from a server,
so only servers need to worry about +set fs_game.

No other directories outside of the base game and current game will ever be referenced by
filesystem functions.

To save disk space and speed loading, directory trees can be collapsed into zip files.
The files use a ".pk3" extension to prevent users from unzipping them accidentally, but
otherwise the are simply normal uncompressed zip files. A game directory can have multiple
zip files of the form "pak0.pk3", "pak1.pk3", etc. Zip files are searched in decending order
from the highest number to the lowest, and will always take precedence over the filesystem.
This allows a pk3 distributed as a patch to override all existing data.

Because we will have updated executables freely available online, there is no point to
trying to restrict demo / oem versions of the game with code changes. Demo / oem versions
should be exactly the same executables as release versions, but with different data that
automatically restricts where game media can come from to prevent add-ons from working.

After the paths are initialized, quake will look for the product.txt file. If not
found and verified, the game will run in restricted mode. In restricted mode, only
files contained in demoq3/pak0.pk3 will be available for loading, and only if the zip header is
verified to not have been modified. A single exception is made for autogen.cfg. Files
can still be written out in restricted mode, so screenshots and demos are allowed.
Restricted mode can be tested by setting "+set fs_restrict 1" on the command line, even
if there is a valid product.txt under the basepath or cdpath.

If not running in restricted mode, and a file is not found in any local filesystem,
an attempt will be made to download it and save it under the base path.

If the "fs_copyfiles" cvar is set to 1, then every time a file is sourced from the cd
path, it will be copied over to the base path. This is a development aid to help build
test releases and to copy working sets over slow network links.

File search order: when FS_FOpenFileRead gets called it will go through the fs_searchpaths
structure and stop on the first successful hit. fs_searchpaths is built with successive
calls to FS_AddGameDirectory

Additionaly, we search in several subdirectories:
current game is the current mode
base game is a variable to allow mods based on other mods
(such as base + missionpack content combination in a mod for instance)
BASEGAME is the hardcoded base game ("base")

e.g. the qpath "sound/newstuff/test.wav" would be searched for in the following places:

home path + current game's zip files
home path + current game's directory
base path + current game's zip files
base path + current game's directory
cd path + current game's zip files
cd path + current game's directory

home path + base game's zip file
home path + base game's directory
base path + base game's zip file
base path + base game's directory
cd path + base game's zip file
cd path + base game's directory

home path + BASEGAME's zip file
home path + BASEGAME's directory
base path + BASEGAME's zip file
base path + BASEGAME's directory
cd path + BASEGAME's zip file
cd path + BASEGAME's directory

server download, to be written to home path + current game's directory

The filesystem can be safely shutdown and reinitialized with different
basedir / cddir / game combinations, but all other subsystems that rely on it
(sound, video) must also be forced to restart.

Because the same files are loaded by both the clip model (CM_) and renderer (TR_)
subsystems, a simple single-file caching scheme is used. The CM_ subsystems will
load the file with a request to cache. Only one file will be kept cached at a time,
so any models that are going to be referenced by both subsystems should alternate
between the CM_ load function and the ref load function.


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