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From: stevem@hpvcfs1.HP.COM (Steve Miller)
Newsgroups: comp.sys.mac.misc
Subject: Re: SetLineWidth: DeskWriter vs LaserWriter
Message-ID: <32730004@hpvcfs1.HP.COM>
Date: 15 Jun 90 23:37:40 GMT
References: <6624@umd5.umd.edu>
Organization: Hewlett Packard, Vancouver, WA
Lines: 32


	
>  (**hPt).h = 1;
>  (**hPt).v = 4;			/* should it be '1' or '4' ? */
>  PicComment(SetLineWidth, sizeof(Point), hPt);
>  MoveTo(20, 160);
>  LineTo(120, 160);
>  MoveTo(20, 180);
>  DrawString("\pThe above line should be 1 point in width.");

I believe that this should produce a 4 point line.  I should because I 
implemented this picComment for the DeskWriter driver.  Let's look at
Mac Tech Note #175 and see what Apple says:

"Before we look at what the SetLineWidth comment does, let's look at the
argument passed to the comment.  The argument is represented as a QuickDraw
Point, however it is interpreted by the LaserWriter as a fraction.
The LaserWriter interprets a point(h,v) to be a real number whose value
is (v/h).  This means that a point whose value is h=2, h=1, will be converted
to 0.5 before being used by the LaserWriter.  If you wanted to pass a value
of 0.25, you would pass a point whose value is h=4, v=1.  For 1.25, pass a
point, h=4, v=5."

It's clear to me that the thickness of the line, in points, is simply the
ratio of v/h.  I don't know why, in your case, the LaserWriter prints the
result with a 1 point thick line.  But from the calculation, the line in
your example should be 4 points thick:  4 pts = 4/72 = about 17 pixels thick at
300 dots per inch.

Steven Miller
Vancouver Division
Hewlett Packard