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From: deadman@garnet.berkeley.edu (Ben Haller)
Newsgroups: comp.sys.mac.programmer
Subject: Re: PICT rowBytes
Keywords: PICT, rowBytes
Message-ID: <1991Apr20.203304.3973@agate.berkeley.edu>
Date: 20 Apr 91 20:33:04 GMT
References: <327@nic.cerf.net>
Sender: root@agate.berkeley.edu (Charlie Root)
Distribution: usa
Organization: Stick Software
Lines: 25

In article <327@nic.cerf.net> moreland@nic.cerf.net (John Moreland) writes:
>vague description in IM V.  On page 52 and 53 the "rowBytes" field of a PICT
>is described, but they don't quite tell how to calculate the "high-bits".
>I know how to calculate the "raw" value of rowBytes, but what "function"
>is used to set the 3 high-bits/flags ?
>
>I am using the "|" operator in C to set the bits, but I noticed that
>a "C view" display from "PICT Detective" shows that they are using "+".
>I know that these lead to very different results, but IM does not seem
>to describe exactly which is correct.
>
>Here are a half dozen or so lines of C code that shows how *I* am
>calculating rowBytes.  Can somebody at Apple tell me which way is
>the "right way" to set the high-bits ?
>
>rowBytes |= 0x8000; /* HIGH-BIT LIT MEANS "PIXMAP" */
>rowBytes &= 0x7FFF; /* UNDO THE HIGH-BIT SO WE CAN USE ROWBYTES "NORMALLY" */

  You should do &= with 0x1FFF, since the three high bits are reserved by
Apple.  Besides this, you're fine.
  x+=0x8000 and x|=0x8000 will produce the same results, BTW, assuming that
the high bit isn't already set, which is true of your example.

-Ben Haller (deadman@garnet.berkeley.edu)
"Shock the monkey to life..." - Peter Gabriel