luatexref-t.pdf.

• if it is positive, it specifies an ‘at size' in scaled points.
• if it is negative, its absolute value represents a ‘scaled' setting relative to the designsize of the font.
The id is the internal number assigned to the font.
The internal structure of the font table that is to be returned is explained in chapter 7. That table is
saved internally, so you can put extra fields in the table for your later Lua code to use.
Setting this callback to false is pointless as it will prevent font loading completely but will nevertheless
generate errors.
4.2 The epdf library
The epdf library provides Lua bindings to many pdf access functions that are defined by the poppler
pdf viewer library (written in C++ by Kristian Høgsberg, based on xpdf by Derek Noonburg). Within
LuaTEX (and pdfTEX), xpdf functionality is being used since long time to embed pdf files. The epdf
library shall allow to scrutinize an external pdf file. It gives access to its document structure, e. g.,
catalog, cross-reference table, individual pages, objects, annotations, info, and metadata.
The epdf library is still in alpha state: pdf access is currently read-only (it's not yet possible to alter
a pdf file or to assemble it from scratch), and many function bindings are still missing.
For a start, a pdf file is opened by epdf.open() with file name, e. g.:
doc = epdf.open("foo.pdf")
This normally returns a PDFDoc userdata variable; but if the file could not be opened successfully,
instead of a fatal error just the value nil is returned.
All Lua functions in the epdf library are named after the poppler functions listed in the poppler header
files for the various classes, e. g., files PDFDoc.h, Dict.h, and Array.h. These files can be found
in the poppler subdirectory within the LuaTEX sources. Which functions are already implemented in
the epdf library can be found in the LuaTEX source file lepdflib.cc. For using the epdf library,
knowledge of the pdf file architecture is indispensable.
There are many different userdata types defined by the epdf library, currently these are Annot,
AnnotBorder, AnnotBorderStyle, Annots, Array, Catalog, EmbFile, Dict, GString,
LinkDest, Object, ObjectStream, Page, PDFDoc, PDFRectangle, Ref, Stream, XRef, and
XRefEntry.
All these userdata names and the Lua access functions closely resemble the classes naming from the
poppler header files, including the choice of mixed upper and lower case letters. The Lua function calls
use object-oriented syntax, e. g., the following calls return the Page object for page 1:
pageref = doc:getCatalog():getPageRef(1)
pageobj = doc:getXRef():fetch(pageref.num, pageref.gen)
But writing such chained calls is risky, as an intermediate function may return nil on error; therefore
between function calls there should be Lua type checks (e. g., against nil) done. If a non-object item
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LuaTEX Lua Libraries