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 00002 00002		Program to Output on Xerox Graphics Printer
 00008 00003	Q-REGISTERS
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	Program to Output on Xerox Graphics Printer
	By Robert Elton Maas, revised by Ralph E. Gorin

Note: This writeup may  become obsolete.  The only reason  it is kept
is that it can  be listed on non-XGP devices.  For XGP listings,  use
the commands:
	R POX
	POX.XGP←POX.POX[CSP,DOC]

	POX is a program for making documents that take advantage of the
special features available on the Xerox Graphics Printer (XGP).  The special
features that POX provides are mainly font switching and text justification.
(There are some other features, but a novice user need not be concerned with
them at present.)

	POX takes a file as input and produces an output file that is suitable
for spooling with the XGP spooler (XSPOOL command).  The input file contains
instructions to POX and the text of the document.  POX takes character sequences
as commands.  Each command sequence is preceded by a character, called the
Escape Character.  The first character in the file (ignoring TV directories
and SOS line numbers) is taken by POX as the escape character.  Thus, the user
gets to specify the escape character.  The escape character can be arbitrary,
but reason dictates that it should be some character that appears infrequently
(or not at all) in the text of the document.  Common choices for the escape
character is \ or $.
In the remainder of this document, the character \ represents the current
Escape Character.

	To run POX, use the system command R POX.  POX wants to see a command
of the form: <OUTPUT FILE>←<INPUT FILE>.  If the <OUTPUT FILE> term is omitted
then the output file will have the same name as the input file, and ".XGP"
extension.  If the extension is omitted on the output file, ".XGP" will be used.

	If all is well with the input file, POX will run and produce an output
file suitable for XSPOOLing.  POX will load the appropriate XSPOOL command into
your line editor, so all you have to do is type return to spool the file.

	(POX may be used as post-processor for some other program. In
this case, POX can accept certain XGP escape sequences at some
places in the file.)

	Below is a list of commands, where
<N> represents a character in the range of 0,1,2,...,9,A,B,...,F
that specifies the font ID number,
<KH> represents any character,
and <FONT> represents a font filename (defaults are .FNT[XGP,SYS])


\|<KH>		(changes the escape character to <KH>)
\M<N><FONT>;	(causes the font to be compiled, and selects it now)
\F<N>		(selects a font which has already been compiled)
\f<N>		(selects a font for just one character,
		then back to old font)
\S		(generates a sample of the currently-selected font,
		see bulletin board)
\;		(everything until next crlf is a comment,
		typed on tty but not included in output file,
		the crlf is flushed totally.  Mostly, this
		command is to break up a very long input line
		without causing <crlf> to appear in the output)
\,		(same as \; except it flushes through next
		page mark or form-feed.  Not valid in paragraph mode.)
\\		(quotes the escape character)
\J		(begins full-justify submode, use \. to exit
		this mode. ONLY the following \-style commands are
		available:  \\ \F<N>.
\R		(begins align-text-against-right-margin-mode,
		until the next <crlf>, \; or \.
		Similar restrictyions as \J mode)
\C		(begins center-the-line mode, similar to \R)
Q-REGISTERS
	There  are  128  registers which can hold any 36-bit integer,
usually the horizonal coordinate of some column on the page. The idea
is    to    allow    specification   of   multi-column   tables   and
superscripts-above-subscripts in an easy and flexable way,  including
automatic  allocation  of  such  things  as "1/5 of a page" by simple
division.  Each register is specified by an  ASCII  character,  hence
some  registers are actually inaccessible, but who cares?  Register 0
(null character, inaccessible usually) is  called  the  "accumulator"
and  is  the  intermediate  storage  for  all sequences of arithmetic
calculation.  Register '56 (the period character)  always  represents
the  current column location. Every time a character is written, this
q-register is updated to  account  for  the  space  used  up  by  the
character,  and  if  you  try  to  write in this q-register, a column
select will be generated in your output file as well as updating  the
q-register  to  reflect  the  column  select. Q-reg's L and R are the
LEFT-MARGIN and the RIGHT-MARGIN. The commands are shown below, where
the  letter  Q  represents  any  character,  and  is used to select a
q-register -- however, if Q is the right-apostrophe "'", then instead
of  reading from a q-register, the octal digits from here to the next
semicolon are assembled into an unsigned constant and  that  constant
acts  as  an immediate operand.  Also, an equal-sign causes a decimal
argument to be scanned up to the next semicolon. Also,  lower-case  w
followed by character gives the width of that character:

\←Q	(Load ac from q-reg)
\+Q	(ac plus q-reg, result in ac)
\-Q	(ac minus q-reg, result in ac)
\¬Q	(q-reg minus ac, result in ac)
\*Q	(ac times q-reg, result in ac)
\/Q	(ac divided by q-reg, result (quotient) in ac)
\\Q	(q-reg divided by ac, result (quotient) in ac)
\~Q	(maximum of ac and q-reg, result in ac)
\_Q	(minimum of ac and q-reg, result in ac)
\→Q	(store contents of ac into q-reg, immediate operand not allowed)
\↑Q	(move text up q/200 inch)
\↓Q	(move text down q/200 inch)
\∩	(up to default superscript location)
\∪	(down to default subscript location)
\⊗	(back to normal baseline, don't forget this!)
\ULABR	(underline from location L to location R,
	on relative scan line A (A positive moves the underline down),
	with line thickness B.  Each of L,A,B,R may be a q-reg or an
	immediate operand)
\j \r or \c
(same as \J \R or \C except they set up temporary margins
  from q-registers l and r)