Path: utzoo!utgpu!watserv1!watmath!att!rutgers!psuvax1!swatsun!jackiw
From: jackiw@cs.swarthmore.edu (Nick Jackiw)
Newsgroups: comp.graphics
Subject: Re: Mac PICT2 specs, a trade secret?
Message-ID: <1990Jul16.173822.6405@cs.swarthmore.edu>
Date: 16 Jul 90 17:38:22 GMT
References: <4421@milton.u.washington.edu> <567@dg.dg.com> <1990Jul15.131748.11053@sics.se>
Reply-To: jackiw@cs.swarthmore.edu (Nick Jackiw)
Organization: Visual Geometry Project, Swarthmore College, PA
Lines: 30

dan@sics.se (Dan Sahlin) writes:
> In Inside Macintosh, there are descriptions of the formats, but I have yet
> failed to find any description on how the 32-bit and 16-bit color pictures
> are compressed.  All I know that some kind of run-length code is used.  
> But keeping the compression algorithms secret makes it impossible to unpack
> the on anything but a Mac.

If you refer to PICT2's compressed bit-image operators, the image data is
encoded by the Mac Toolbox's PackBits() routine (and decoded by UnpackBits).
These routines manipulate a format which is documented in the Macintosh
Tech Notes (#171, if memory serves).  These too are available from apple.com.


> PS.  Does anyone have any ideas how the dithering is performed in 32-bit
> Color Quickdraw?  It seems to work very well, and I can display a dithered
> version of color pictures even on a black and white Mac SE/30.
> Unfortunately this feature is for some reason disabled on a Mac Plus.


Color QuickDraw, and its 32-bit superset, are written in 68030 code.  The
Mac plus is a 68000.  The feature is not disabled; it is nonexistent.




-- 
-----Nicholas Jackiw [jackiw@cs.swarthmore.edu|jackiw@swarthmr.bitnet]-----
"... Then, with an infernal shovel that increases my strength, I dig out of
that inexhaustable mine whole chunks of lice, big as mountains.  I split them
up with an axe and I transport them in the depths of night to city streets."