Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!uwm.edu!wuarchive!husc6!sunfs3!kent
From: kent@sunfs3.camex.uucp (Kent Borg)
Newsgroups: comp.sys.mac.programmer
Subject: Re: Programming and the 8/24 GC card
Summary: 32-Bit QuickDraw has off-screen support
Message-ID: <666@sunfs3.camex.uucp>
Date: 27 Mar 90 16:35:16 GMT
References: <2344@husc6.harvard.edu>
Reply-To: kent%lloyd@husc6.harvard.edu (Kent Borg)
Organization: Camex, Inc., Boston, Mass USA
Lines: 48

In article <2344@husc6.harvard.edu> fry@brauer.harvard.edu (DSF2) writes:
>
>Reading through Apple Direct, I was thrilled to see that some
>level of multiprocessing is afforded by the new 8/24 GC accelerated 
>graphics card.  If a program calls a QuickDraw routine,
>the GC's AMD 29000 is given responsibility for executing it.
>The 29000 tells the CPU that the routine has already finished
>(which is a lie) and the CPU goes on to the next instructions
>while the 29000 performs the QD routine.  Should the
>CPU encounter another QD instruction before the 29000 finishes, 
>it will wait for the 29000. 
>
>My worry is what level of compatibility is required from a
>program to make this work.  Certainly Apple has always warned
>us that we should user their routines to do QuickDraw, but
>for some applications this is just too slow.  What happens if
>you try to do this with the GC installed?

Apple has thought of that--at least for new code.  Get the notes on
32-Bit QuickDraw.  They now have explicit support for off-screen
graphics.  One of the calls says: "GetPixBaseAddr waits until all
drawing to the PixMap is completed..."

What about compatibility with old code?  I suspect that the 29000 only
operates on the GC card memory.  Any QuickDraw outside of it will be
old fashioned.  From the spec sheet:

  Optional Macintosh Display Card DRAM Expansion Kit: Lets users
  add on-board dynamic RAM (DRAM) to boost the performance of
  applications that use off-screen bitmaps and other graphics
  techniques.

I think it is a good idea to start using these new gworlds.

The other calls are: NewGWorld, LockPixels, UnlockPixels,
AllowPurgePixels, NoPurgePixels, GetPixelsState, SetPixelsState,
GetGWorldDevice, UpdateGWorld, DisposeGWorld, and SetGWorld.

Slight catch: Folks with II's, IIx's, IIcx's, and hacked SE/30's might
run the 8-24 GC card without 32-Bit QuickDraw.  Off-screen graphic
worlds might not be there.  These would seem like strange people who
buy a fancy video card but don't use the matching fancy software, but
we still don't want to crash on them.

-- 
Kent Borg                lloyd!kent@husc6.harvard.edu  or  ...!husc6!lloyd!kent
MacNet: kentborg                              H:(617) 776-6899  W:(617)426-3577
"So simple minded.  Kindergarten level with no content, but it's beautifully 
landscaped, and the architecture is interesting."    -my mother on Epcot Center