Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!usc!apple!apple.com!casseres
From: casseres@apple.com (David Casseres)
Newsgroups: comp.sys.mac.programmer
Subject: Re: Page Rectangles (Reply part two)
Message-ID: <10639@goofy.Apple.COM>
Date: 9 Oct 90 21:51:27 GMT
Sender: usenet@Apple.COM
Organization: Apple Computer, Inc.
Lines: 58
References:<10585@goofy.Apple.COM> <6156@ethz.UUCP>

In article <6156@ethz.UUCP> czychi@ethz.UUCP (Gary Czychi) writes:
> Meanwhile I've got a mail from Sean Parent <sean_parent.snarkmail_l_z>. 
He
> says (I hope I am allowed to quote him):
> 
> > Once upon a time an Apple engineer wrote some code to calculate the
> > page size for the ImageWriter. Unfortunatly, he didn't realize that
> > his calculations where poor and didn't always make best use of the
> > machine.

I just talked with Sean about this.  The calculation is one which may 
cause an error of one or two dots in the width of an ImageWriter page.
Apparently it causes more trouble in the ImageWriter LQ.


> > ...Well, the
> > ImageWriter code was also used in the LaserWriter SC adjusted for the
> > memory requirements of that device with all of the same original bugs,
> > yet new and different printable areas. This is one of the worst cases
> > of propagating bugs that you will ever see. Unfortunatly it cannot be
> > fixed in existing drivers without reformatting everybodies documents.

Sean was mistaken about this.  The LaserWriter SC code that calculates 
page rectangles is not derived from the ImageWriter code, and does not 
have any bugs related to the one described above.

> Let's summarize:
> There *is* something wrong with the calcuation of the page rect, but it
> wouldn't be opportune for Apple to change it in the near future. And as
> far as I know, there's no patch which can be applied to the driver(s)
> to change it to more reasonable values.

In the case of the ImageWriter there is apparently a discrepancy in 
certain cases of a couple of dots.  In the case of the LaserWriter SC, I 
can see that in the case of A4 paper you are mistaken about what the page 
rectangle is, and in the case of legal paper the rectangle is not what you 
think it ought to be.  I don't think it is fair, on this basis, to claim 
that "there *is* something wrong."  Your position that the values are not
reasonable is based on your error about the A4 page rect, and on an
oversimplified assumption about the relationship between RAM size and
the legal-size page rect.

> BTW, the memory of the LW SC can hold 1.048.576 bits. How much room is
> left in there for the actual page? The page is prepared in the Mac
> itself, so in the printer should be enough room for the *very big* page
> rectangle.

The bitmaps that make the page image are built one at a time in the Mac.  
In the printer there is firmware that runs the SCSI bus, receives the 
bitmaps, deposits them in the frame buffer, and controls the mechanism.  
This firmware uses the printer RAM in various ways, besides the frame 
buffer;  how much of the RAM is available for the frame buffer, and how 
efficiently it is utilized, is not self-evident -- and I don't know the 
answer, except that in the case of legal paper, the rectangle that is 
calculated is the largest one that will work.

David Casseres
     Exclaimer:  Hey!