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From: dgold@apple.UUCP
Newsgroups: comp.sys.mac
Subject: Re: Program compatability between Mac ][ and Classic Mac...
Message-ID: <687@apple.UUCP>
Date: Thu, 30-Apr-87 13:21:16 EDT
Article-I.D.: apple.687
Posted: Thu Apr 30 13:21:16 1987
Date-Received: Fri, 1-May-87 06:39:50 EDT
References: <9575@decwrl.DEC.COM>
Reply-To: dgold@apple.UUCP (David Goldsmith)
Organization: Apple Computer Inc., Cupertino, USA
Lines: 43

In article <9575@decwrl.DEC.COM> harrow@exodus.dec.com (Jeff Harrow, NCSE BXB1-2/E02 DTN=293-5128) writes:
>Regarding this issue, however, how about some  type of patches in 
>the  "lower"  systems  (non  Mac  ][ at this  point)  which  will 
>AUTOMATICALLY  translate   the  "color"  (and  other  unsupported 
>calls/structures) into a form which WILL work.

We have tried to do this where data compatibility is concerned, e.g., there
is a patch to DrawPicture on the 128K ROM and SE to be able to play back the
new color pictures produced on the Mac II.  However, there are two reasons
it is not really feasible to go farther than this:

1. The new color traps are in a range which doesn't exist on anything except
   the Mac II.  They are Toolbox traps in the range AA00-ABFF.  The Toolbox
   trap table on the Mac Plus and SE is not big enough to hold these traps.
   To change this would require patching the trap dispatcher, which would
   slow things down a bit on those machines.

2. Color QuickDraw represents a large amount of new effort over old QuickDraw.
   There are many new data structures which would have to be interpreted or
   converted to process the new calls.  In order to fully support color
   programs, we would have to support the new CGrafPort (color GrafPort)
   structure, which is laid out differently.  Since the GrafPort data
   structure lies at the heart of QuickDraw, we would have to patch out
   most or all of QuickDraw, which isn't really feasible (it might take
   80K-100K of patches).  Finally, color QuickDraw uses 68020 instructions
   heavily to speed it up, so the be supported on a 68000 it would have to
   be modified.

For MacApp 1.1 we have modified one of our sample programs (DrawShapes) to
support color, and it really is not that hard to draw things differently
depending on what machine you're running on.  The changes to MacApp itself
to support color were not that great.  It's unfortunate that we can't make
the incompatibilities vanish altogether, but in this case it would come
at a large cost.  Oh well.
-- 
David Goldsmith
Apple Computer, Inc.
MacApp Group

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