dvips: Bitmap font encodings
6.1.5 Bitmap font encodings
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To dvips, bitmapped fonts do not have any notion of linguistics; they
are simply a vector of glyphs. By comparison, PostScript fonts are
required to contain an encoding vector that at least provides glyph
names; these names can permit PostScript and PDF viewers to extract
legible text from Postscript and PDF output.
Unlike previous versions, dvips versions 2020 and later add glyph
naming information to Type 3 bitmapped fonts (if they can locate such
information) as an Encoding vector. This provides some support for
search, for copy and paste, and even some limited support for
file commands::) enable and disable this functionality; by default it is
set to enabled, without warnings.
To do this, dvips must find encoding information for the bitmapped
fonts. It does this by first searching for a font-specific encoding
file; for instance, for cmr10, it will search for 'dvips-cmr10.enc' in
the standard encoding path. If it does not find such a file, it will
search for a 'dvips-all.enc' file which contains a base set of encodings
for many fonts.
The specific syntax of an encoding file is unspecified, except that
it must be a PostScript fragment that leaves exactly one object on the
operand stack. (This is different from the encoding files used to
define encodings for PostScript fonts, described earlier). Normally
that object is just an array of 256 names; in this case, that array is
used as the encoding vector for the font. Alternatively, the object can
be a procedure that, when executed, leaves a legal encoding vector on
the stack. This second option is made available to support future
enhancements that may add additional constructs to the font dictionary
to enhance the interpretation of font characters.
The 'dvips-all.enc' file contains encodings for many fonts, and it is
loaded by dvips at most once. The format is just a sequence of font
names, one per line, each terminated by a colon, followed by the
encoding to use for those files.
As part of its operation, to enable heuristics in PostScript and PDF
viewers to properly identify word breaks and column gutters, dvips also
generates a modified font bounding box and a modified font coordinate
system.
Info Catalog
dvips: Encodings
dvips: Font concepts
dvips: PostScript typesetting