Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!purdue!ames!oliveb!apple!apple.com!casseres
From: casseres@apple.com (David Casseres)
Newsgroups: comp.sys.mac
Subject: Re: How do you tell a laser font?
Message-ID: <1796@internal.Apple.COM>
Date: 11 May 89 22:36:57 GMT
Sender: usenet@Apple.COM
Organization: Apple Computer, Inc.
Lines: 63

In article <2371@mace.cc.purdue.edu> ajq@mace.cc.purdue.edu (John 
O'Malley) writes:
> As I understand it, there are two major kinds of fonts:  screen fonts and
> printer fonts.

"Bitmap" and "outline" fonts are better terms.  A screen font is just a 
bitmap font that matches a particular outline font.  Bitmap fonts can be 
displayed on the screen, or they can be printed.  Adobe's outline fonts 
are only used for printing, in a Mac system; but on other systems like 
Next they are also displayed on the screen.  Apple's outline fonts, 
announced this week, will be used for both screen display and printing.

> A screen font is that which you have installed in the System file on your
> Macintosh.

Bitmap fonts are normally installed in the system file, but with Suitcase 
and similar utilities they can be in some other file or files.  Adobe 
outline fonts may be built into a printer or they can be downloaded to the 
printer from files on the Mac.

> To print a font on an ImageWriter, a Macintosh takes the screen font's
> double, scales it down 50%, and then prints it.  That's how it achieves
> fairly-good looking font output.  Example:  You have both 12- and 
24-point
> New York installed in your System file.  You want to print a document 
done
> in 12-point New York.  You tell the Mac to print in "best" quality mode.
> The Mac takes the 24-point screen font, scales it down 50% to 12-point,
> and then sends the page to the ImageWriter.

The scaling occurs just by printing at 144 dots/inch instead of 72.  The 
Mac draws in an offscreen bitmap with the 24-point font, then sends the 
bitmap directly to the printer, which gets 12-point size (and nice 
quality) just by having its dots closer together than the Mac screen.

> A key point to recognize is that when you print a document on the
> ImageWriter, the Macintosh does all the thinking.  It creates a bitmap
> picture of the document within its memory, and then slowly spits out this
> picture to the printer for printing.

It doesn't actually draw the whole document or even a whole page at any 
one time; it just draws horizontal strips across the page, one after 
another.

> To print a font on the LaserWriter, a Macintosh looks at the screen font
> that you've used and sees if the equivalent printer font is installed in
> the LaserWriter.  If so, then it sends the document to the LaserWriter,
> which in turn uses its PostScript brain and built-in printer font to 
print
> the page.  The major work is done by the LaserWriter, not the Mac.

Well, no.  The application "draws" the page (which may contain graphics as 
well as text) using a sequence of QuickDraw calls, as if it were drawing 
to an offscreen bitmap -- or as if it were printing on an ImageWriter.  
The LaserWriter driver captures these calls and translates them into a 
PostScript program -- no mean trick, since QuickDraw and PostScript have 
entirely different models of how drawing happens.  The driver sends the 
PostScript program to the LaserWriter, which executes it.  The work is 
rather evenly divided between the Mac and the printer.

David Casseres

Exclaimer:  Wow!