Specifications

B-7Calculatin Page Width Using Printer Colon File Escape Sequence
47.%d – Pops the 128 off the stack and returns it, in ASCII format, to the in–progress
calculation of ia, the input data stream pipeline for ASCII jobs.
Why the Stack Language Describing Page Width Works
The LaserPrinter 4029 Series technical reference contains a figure and a table that together
describe the printable and unprintable areas on a page, and the paper and envelope
dimensions, in pels, for standard paper and envelope sizes. For example, the printable area
on an 8.5 x 11 (width by length) inch page is 2400 x 3200 pels (width by length). Note that if
the page is rotated either 90 or 270 degrees for landscape printing, the dimensions are
swapped and become 3200 x 2400 pels (width by length).
The evaluation of %IwW begins by checking to see if the w flag was used on the command
line; if it was, then there are no calculations to perform. The requested value will be used.
(That is not a promise that it will work, just that it will be used.) If the w flag was not used on
the command line, then piobe has to figure out how wide the page is under the current job
environment, as determined by other command line flags and by colon file defaults.
The first item checked in the evaluation of _w (page width) is page orientation (_z). As
noted above, rotating the page by odd multiples of 90 degrees flips the page dimensions.
Looking at the if–then–else statement that is the beginning of the definition of wK, it can be
seen that the value of _z is a switch that controls which of wJ and wK will be used for page
width. If the page has a portrait orientation, then wJ is width. If the page has a landscape
orientation, then wK is width. After the page width in pels is resolved, the remainder of the
escape sequences in the definition of wK just take pitch and character–width (double wide
or not) into account while converting the number of pels to the number of characters.
The wK attribute is selected because the page orientation is landscape. Thus far all that is
known is that the dimensions have been flipped; what the dimensions actually are is still
unknown. The evaluation of wK begins by fetching the value (if any) of a command line
usage of the Q flag, which is a printer–dependent value requesting a specific paper size. If
the Q flag was used on the command line, then that value will be used to select the paper
width in pels, otherwise a value for Q will be determined by evaluating Wu, which is a value
for the paper source based on the attributes _O (type of input paper handling) and _u (input
paper source). Note that _Q is defined as %IwQ, whose definition begins with %IWu.
Because Q was not used on the command line, the evaluation of Wu determines that the O
flag wasn’t used either, and so executes the else clause in the outer if–then–else statement
in the definition of Wu, returning the default colon file value of _u, 1, to the evaluation of wQ.
Because this is as deep as the nesting of escape sequences goes for the evaluation of _w,
it is worth taking a closer look at the logic defining Wu. Keep in mind the definitions and
legal values for O, u, and Q, which are:
• O – type of input paper handling – 1 (manual), 2 (continuous forms), 3 (sheet feed) –
default is sheet feed.
• u – input paper source – 1 (primary), 2 (alternate), 3 (envelope) – default is primary.
• Q – paper size for input paper source – values are printer–dependent – defined by
combination of O and u.
The escape sequences defining Wu say this:
• Case 1: If the O flag was not used on the command line, then return the colon file default
value for _u. For example, if the user did not specify a type of input paper handling, then
return the input paper source (either from the command line or the default from the colon
file) to the evaluation of %IwQ.
• Case 2: If the O flag was used on the command line but its value was not 1, then return
the colon file’s default value for _u. For example, if the user–specified a type of input
paper handling other than manual,then return the input paper source (either from the
command line or the default from the colon file) to the evaluation of %IwQ.