View source for AGIWiki/Vol file

{{AGIWiki}}

Vol files store the data for an AGI game. They are essentially little more than files which have jammed all the [[AGIWiki/Logic|logic]], [[AGIWiki/Picture|picture]], [[AGIWiki/View|view]], and [[AGIWiki/Sound|sound]] resources together in a single file. Most games have multiple Vol files for two reasons:

* the original distribution media for AGI games was 360 KB floppy disks; most games were larger than 360 KB – multiple Vol files allows the game to be split across multiple disks
* due to the way the Vol files are indexed, they have a rough maximum of 1 MB in size

There is no required ordering of the resources within a Vol file. The resources are indexed in the LOGDIR, PICDIR, VIEWDIR, and SNDDIR files, which contain entries for every resource in the game, indicating which Vol file the resource appears in and where in that Vol file it appears. See [[AGIWiki/Directory files|directory files]].

Another limitation imposed by the way the directory files are stored is that there can be only 16 Vol files. As a practical matter, this is well above the limit required by any existing AGI game.

Each resource in a Vol file contains a header that is followed by resource-specific data, as described in the following sections:

== Version 2 format ==

{| class="wikitable" style ="border: 1px solid black;"
! Byte
! Meaning
|- 
| 0-1
| Signature (always 0x12 0x34)
|-
| 2
| Vol number that the resource is contained in
|-
| 3
| Length of the resource, not including the header
|}

As is clear from this table, 3 of the 5 bytes provide fairly useless information. The most interesting bytes are bytes 3 and 4, which give the size of the resource. Because this value is two bytes in length, resources can never be any larger than 65535 bytes.

== Version 3 format ==

(to be filled in)