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From: palmer@tybalt.caltech.edu (David Palmer)
Newsgroups: comp.sys.mac
Subject: Re: Help wanted: LSC, MacPaint
Message-ID: <4096@cit-vax.Caltech.Edu>
Date: Tue, 29-Sep-87 16:00:20 EDT
Article-I.D.: cit-vax.4096
Posted: Tue Sep 29 16:00:20 1987
Date-Received: Thu, 1-Oct-87 05:31:26 EDT
References: <3320023@hpcid.HP.COM>
Sender: news@cit-vax.Caltech.Edu
Reply-To: palmer@tybalt.caltech.edu.UUCP (David Palmer)
Organization: California Institute of Technology
Lines: 36

In article <3320023@hpcid.HP.COM> tedj@hpcid.HP.COM (Ted Johnson) writes:
>
>The following 90 line program is my attempt at using a SFGetFile dialog
>to select a MacPaint file, and then using CopyBits to display the file
>on the Mac's screen.  This program is meant to be a Lightspeed C version
>of Technical Note #86, which gave a Pascal example for reading a MacPaint
>file.
>
>Unfortunately, this program displays junk (it looks like "snow" on a
>TV screen) on the Mac's screen instead of the MacPaint picture.  Any clues
>as to where I'm going wrong would be greatly appreciated!  (I suspect that
>my syntax in calling CopyBits() is wrong...)
...
>	
>	for (scanLine = 1; scanLine <= 720; scanLine++) {
>		UnpackBits(srcPtr, dstPtr, 72);
>	}

If UnpackBits() is defined with srcPtr and dstPtr as VAR, then the line
should be:
		UnpackBits(&srcPtr, &dstPtr, 72);
The loop as it stands does not change srcPtr and dstPtr so you do the
same thing 720 times, and the wrong thing to boot.  In C, you 'call by
name' by passing a pointer to an object.

Stylistic note: most C programmers would write the first line:
	for (scanLine = 0 ; scanLine < 720 ; scanLine++)
because this would allow the use of scanLine as an array index.  (In C,
a 720 element array has indices from 0 to 719, inclusive).  This is unimportant
in this case, but you might as well be consistent.

		David Palmer
		palmer@tybalt.caltech.edu
		...rutgers!cit-vax!tybalt.caltech.edu!palmer
	The opinions expressed are those of an 8000 year old Atlantuan
	priestess named Mrla, and not necessarily those of her channel.