Path: utzoo!attcan!utgpu!jarvis.csri.toronto.edu!mailrus!tut.cis.ohio-state.edu!bloom-beacon!bu-cs!dartvax!eleazar.dartmouth.edu!earleh
From: earleh@eleazar.dartmouth.edu (Earle R. Horton)
Newsgroups: comp.sys.mac.programmer
Subject: Re: Aligining bitmaps?
Message-ID: <15291@dartvax.Dartmouth.EDU>
Date: 29 Aug 89 06:10:39 GMT
References: <3791@ncsuvx.ncsu.edu> <15288@dartvax.Dartmouth.EDU> <3967@internal.Apple.COM>
Sender: news@dartvax.Dartmouth.EDU
Reply-To: earleh@eleazar.dartmouth.edu (Earle R. Horton)
Organization: Thayer School of Engineering
Lines: 28

In article <3967@internal.Apple.COM> lsr@Apple.COM (Larry Rosenstein) writes:
>In article <15288@dartvax.Dartmouth.EDU> earleh@eleazar.dartmouth.edu 
>(Earle R. Horton) writes:
...
>Finally, I'm not sure that a word boundary is optimal alignment for Color 
>Quickdraw.  I think you might want to use longword alignment.  I haven't 
>done any stuff with offscreen pixmaps, so I don't know for sure.
...
>>      I don't notice any difference between aligned or non-aligned
>> BitMaps with a black and white screen.  On the other hand, these are
>> subjective results since I haven't done formal timing.
>
>On a MacPlus it is noticeable, although I haven't done any formal 
>measurements, either.

     OK, I broke out the old Timex, and actually timed some big screen
animation on the Mac II using 1, 2, and 4 bits screen depth with big
offscreen PixMaps.  My conclusion after about a half hour of testing
was that the only alignment that makes any difference to Color
QuickDraw CopyBits() is longword alignment.  The performance increase
when both PixMaps are longword-aligned is what I would call
spectacular, too.  It's about 2 to 1!  There does appear to be little,
if any, performance increase for byte or word alignment over random
alignment, so I wasn't totally wrong before.

     Sorry for any confusion my earlier posting might have caused.

Earle R. Horton