OS3.1 hard disk volume icon

[Thomas]

Under OS4, there are some extra defaulting mechanisms

The idea is not so new. Already since Kick 2.0 you can override some default icons by placing them in Envarc:sys:

def_disk.info
def_drawer.info
def_tool.info
def_project.info
def_trashcan.info
def_kick.info

And the extension called DefIcons was made for OS 3.1 by the NewIcons author. It was later taken over into OS 3.5 as an official interface rather than the hack it was before.

[Thomas]

I believe those arrived during OS 4.x some time.

No, DefIcons could do this from the beginning.

[Thomas]

Really?

There is a file called deficons.prefs in env: resp. envarc: which defines all recognised file types. It's a binary file but its structure is documented in the NewIcons developer docs. OS 3.9 contains an editor for the file which allows do define new file types.

For each recognised file type you can create a def_<filetype>.info in envarc:sys to override the default icon.

For drives you can use def_<drivename>.info or def_<volumename>.info in OS 3.5+ or def_<drivename>disk.info in OS 3.1 (for example def_RAMdisk.info).


(Note: I wrote all this from memory, so no guarantee that every aspect is correct. If you want the definite truth, you should RTFM.)