Make TopDict's defaultWidthX and nominalWidthX Optional<>s so that
we can check if they're set per fdselect-selected font dict, and
if so use the value from there in CID-keyed fonts. Otherwise, keep
using the value in the top dict.
The fdselect array (that we already read) maps eachs glyph ID
to an fdarray index. The font dict at that index then stores
information for that glyph.
In practice, this is used to assign different defaultWidthX /
nominalWidthX values to blocks of glyphs in CID-keyed fonts.
We don't do anything yet with the data, and we also don't send
data of CID-keyed CFFs into this parser either, so no behavior
change.
This happens for CFFs that contain multiple fonts. This doesn't
happen in practice, but the same code will be used for fdarray
parsing, which will contain several dicts.
No behavior change.
This is one of the two top dict entries we need for CID-keyed fonts.
We don't send any CID-keyed font data into the CFF parser yet,
so no behavior change.
No behavior change, except that we now dbgln() if we see a
PrivDictOperator we don't know about. (I haven't seen this in
practice, but I found this useful while debugging things.)
...and do string expansion at the call site.
CID-keyed fonts treat the charset as CIDs instead of as SIDs,
so having access to the SIDs in numberic form will be useful
when we implement support for CID-keyed CFF fonts.
No behavior change.
...and replace template instantiations with a loop, to make this
easily possible.
Vaguely nice for code size as well.
Needed for example in 0000054.pdf and 0000354.pdf in 0000.zip in the
pdfa dataset.
Font programs are bytecode programs defining glyphs. If several glyphs
share a piece of outline, that opcode sequence can be put in a
subroutine ("subr") table and the definition of those glyphs can then
call that subroutine by number, to reduce file size.
CFF fonts can in theory contain multiple fonts, and so there's a global
subr table shared by all the fonts in one CFF, and a local per-fornt
subr table. We used to only implement the local subr table, now we
implement both.
(We only support one font per CFF, and at least in PDF files, that's
all that's ever used. So a global subr table isn't very useful.
But the spec explicitly allows it -- "Global subroutines may be used in
a FontSet even if it only contains one font." -- and it happens in
practice.)
The main encoding data maps glyph ID ("GID") to its codepoint.
If a glyph has several codepoints, then a secondary table mapping
codepoint to string ID ("SID") of the glyph's name is present.
(A separate table associates each glyph with its name already.)
I haven't seen this used in the wild, but the structure of the
supplemental data is also going to be needed for built-in encodings.
Only really useful for reading SIDs in the Top DICT (copyright
text etc), which we currently don't do.
I haven't seen a difference from looking things up in the string
table. The only real effect from the commit that I need is that
it pulls a local resolve() labmda into a real function
resolve_sid(), which I want to call in a future commit.
But it makes things more spec-compliant, and if we ever want to
read SIDs in metadata in the future, now we can.
We'd unconditionally get the int from a Variant<int, float> here,
but PDFs often have a float for defaultWidthX and nominalWidthX.
Fixes crash opening Bakke2010a.pdf from pdffiles (but while the
file loads ok, it looks completely busted).
The first iteration has enough SIDs to display simple documents, but
when trying more and more documents we started to need more of these
SIDs to be properly defined. This is a copy/paste exercise from the CFF
document, which is tedious, so it will continue in small drops.
This commit fills all the gaps until SID 228, which covers all the
ISOAdobe space, and should be enough for most use cases. Since this is a
continuous space starting at 0, we now use an Array instead of a Map to
store these names, which should be more performant. Also to simplify
things I've moved the Array out of the CFF class, making it a simpler
static variable, which allows us to use template type deduction.
The Compat Font Format specification (Adobe's Technical Note #5176) is
used by PDF's Type1C fonts to store their data. While being similar in
spirit to PS1 Type 1 Font Programs, it was designed for a more compact
representation and thus space reduction (but an increment on
complexity). It also shares most of the charstring encoding logic, which
is why the CFF class also inherits from Type1FontProgram.
This initial implementation is still lacking many details, e.g.:
* It doesn't include all the built-in CFF SIDs
* It doesn't support CFF-provided SIDs (defaults those glyphs to the
space character)
* More checks in general
