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POSTSCRIPT
2-18 XEROX DOCUPRINT NPS GUIDE TO USING PAGE DESCRIPTION LANGUAGES
Printer Controller operations
The DocuPrint NPS Printer Controller operates as follows:
• PostScript stdout messages are printed on the “JOB
MESSAGES AND ERRORS” page. DocuPrint PostScript prints
error messages directed to %stderr on the “JOB MESSAGES
AND ERRORS” page as well.
• PostScript font substitution error messages appear on the “JOB
MESSAGES AND ERRORS” page only when the requested
font is not present and is not one of the DocuPrint base 51 font
set.
• DocuPrint does not emulate the serial communications
handling aspects of the LaserWriter. Notably, DocuPrint
syntactically treats control-D and control-Z as literal characters
in ASCII strings and binary data, not as end-of-file delimiters.
Also, DocuPrint does not strip high bits from character string
data. Instead DocuPrint treats all input bytes as valid
PostScript.
• DocuPrint handles ASCII or binary input transparently and does
not require two input modes.
• DocuPrint wraps each PostScript document with a save and
restore to ensure that documents are independent. DocuPrint
NPS implements the exitserver operator to permit modifying
PostScript virtual memory within a document, but not across
documents.
• DocuPrint performs standard PostScript error handling when it
encounters LaserWriter-specific operators that DocuPrint NPS
does not implement. The error handling process produces a
standard PostScript “undefined command” message and
flushes the master to end-of-file.
Scan conversion details
DocuPrint NPS uses the scan conversion rules to control the
PostScript painting operators stroke, fill, clip, and image.
The scan conversion process and rules are not defined as part of the
PostScript language. They are subject to variations depending on
algorithms used in different PostScript printing devices to achieve the
most accurate rendition possible. The sections below describe the
stroke and fill operators.
Stroke
Stroke refers to painting a line that follows the current path, is
centered on the path, and has sides parallel to the path segment.
“Path” includes a thickness set by the operator setlinewidth.
DocuPrint NPS turns on any device pixels whose centers lie within
the width of the path to be stroked. The pixels whose centers lie
outside of the width of the path are turned off.