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From: info-mac@uw-beaver (info-mac)
Newsgroups: fa.info-mac
Subject: Icons
Message-ID: <2302@uw-beaver>
Date: Wed, 21-Nov-84 01:24:40 EST
Article-I.D.: uw-beave.2302
Posted: Wed Nov 21 01:24:40 1984
Date-Received: Thu, 22-Nov-84 07:42:17 EST
Sender: yenbut@uw-beave
Organization: U of Washington Computer Science
Lines: 50

From: c55-dx%D.CC@Berkeley

     I don't have much knowledge about the inner workings of a Mac but my
experiences seem to support the explanation of icons seen here.  The file
Creator and the contents of the DeskTop seem to have the most bearing.  I am
describing my exploits in the hope that they will be useful to some of you out
there.
     I have successfully changed a file's icon using the Icon Editor and
FEdit.  Be sure you do all of the work on a separate, trashable disk (yes,
I screwed up desktops in my first attempts).  Use snapshots, MacPaint, and
the Icon Editor to get hex representations of the icon and its inverse.  Then
use FEdit on the file whose icon you want to change.  Search for the hex
representations of the the icon and substitute it with the new icon (designed
using the Icon Editor).  Do the same for the new inverse.  (The inverse
should simply be the icon filled in with black.  The desktop seems to 'or'
the inverse with the icon on the screen to invert it and use the fill the
area defined in the inverse with gray patterns when the disk is ejected, etc.
The inverse also seems to define the area where the mouse pointer will be able
to select the icon.  Interesting inversions can be formed by playing with the
inverse but if it has 'holes', it is hard to use.  e.g. Sargon III).  After
doing this, the icon will not change in appearance.  The new icon can be
obtained by changing the file's Creator (be sure to change any references to
the Creator inside the file).  
     The new icon can also be changed by playing DeskTop file.
(I don't think it is possible to have two files with the same Creator and
two different icons.)  The DeskTop files on disks which have seen the icon
before will have to be patched.  Just use FEdit on the DeskTop file and remove
any references to the Creator of the file.  Using this method, the Creator
doesn't have to be changed.  References to the Creator can be removed by simply
replacing the four letters with four blanks.  (I think this makes the desktop
use the icon representations in the file itself instead of the old ones stored
in the DeskTop.  WARNING:  Putting blanks in the file may have an adverse effect.
I have not noticed any though.  Does anyone know if this quick fix is okay?)
     Fidgetting with the DeskTop also helped me in another situation.  I got
a disk from a local users group with public-domain MS-BASIC programs.
The program icons were generic document icons instead of MS-BASIC program icons.
When I put MS-BASIC on the disk, the MS-BASIC icon disappeared and MS-BASIC
took on a generic application icon.  By blanking out references to MSBA and
MSBB in the DeskTop, I got the correct icons to appea.
     Well, that's it.  This method should work for almost anything if you know
what to search for and are willing to go through tedious hex representations.
I would be glad to hear of any more elegant methods that you uncover.  Lastly,
apologies to other readers if this is too long, confusing, or uninteresting.

                                      Lloyd Lim
                                      c55-dx @d (@ UC Berkeley)

P.S.  Does anyone know of a fix to the Missile Command MS-BASIC game written
  by Steven Weintraut?  It bombs quite often with a subscript out of range
  error in line 2040.