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LibPDF: Initial support for drawing CFF-based Type0 fonts

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Together with the already-merged #23122, #23128, #23135, #23136, #23162,
and #23167, #23179, #23190, #23194 this adds initial support for
rendering some CFF-based Type0 fonts :^)

There's a long list of things that still need improving after this:

* A small number of CFF programs contain the charstring command 0,
  which is invalid. Currently, this makes us reject the whole font.

* Type1FontProgram::rasterize_glyph() is name-based. For CID-based
  fonts, we want a version that takes CIDs (character IDs) instead.
  For now, I'm printing the CID to a string and using that, yuck.
  (I looked into doing this nicely. I do want to do that, but I
  need to read up on how the `seac` type1 charstring command uses
  character names to identify parts of an accented character.
  Also, it looks like `seac`'s accented character handling moved
  over to `endchar` in type2 charstring commands (i.e. in CFF data),
  and it looks like we don't implement that at all. So I need to do
  more reading first, and I didn't want to block this on that.)

* The name for the first string in name-based CFF fonts looks wrong;
  added a FIXME for that for now.

* This supports the named Identity-H cmap only for now. Identity-H
  maps UTF16-BE values to glyph IDs with the idenity function, and
  assumes it's horizontal text. Other named cmaps in my test files are
  UniJIS-UCS2-H, UniCNS-UCS2-H, Identity-V, UniGB-UCS2-H, UniKS-UCS2-H.
  (There are also 2 files using the stream-based cmaps instead of the
  name-based ones.)

  * In particular, we can't draw vertical text (`-V`) yet

* Passing in the encoding to CFF::create() is awkward (it's nullptr
  for CID-keyed fonts), and it's also not necessary since
  `Type1Font::draw_glyph()` already does the "take encoding from PDF,
  and only from font if the PDF doesn't store one" dance.

* This doesn't cache glyphs but re-rasterizes them each time. Easy
  to add, but maybe I want to look at rotation first. And things
  don't feel glacial as-is.

* Type0Font::draw_glyph() is pretty similar to second half of
  Type1Font::draw_glyph()
This commit is contained in:
Nico Weber 2024-02-15 07:54:08 -05:00 • committed by Tim Flynn
parent c9d48bbca4
commit bd74447dba
2 changed files with 50 additions and 7 deletions
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19
Userland/Libraries/LibPDF/Fonts/CFF.cpp
View file

@ -246,11 +246,24 @@ PDFErrorOr<NonnullRefPtr<CFF>> CFF::create(ReadonlyBytes const& cff_bytes, RefPt
for (size_t i = 0; i < glyphs.size(); i++) {
if (i == 0) {
TRY(cff->add_glyph(0, move(glyphs[0])));
if (top_dict.is_cid_keyed) {
// FIXME: Do better than printing the cid to a string.
auto cid = 0;
TRY(cff->add_glyph(ByteString::formatted("{}", cid), move(glyphs[0])));
} else {
// FIXME: Shouldn't this use resolve_sid(0, strings) (".notdef") as name?
TRY(cff->add_glyph(0, move(glyphs[0])));
}
continue;
}
auto const& name = charset_names[i - 1];
TRY(cff->add_glyph(name, move(glyphs[i])));
if (top_dict.is_cid_keyed) {
// FIXME: Do better than printing the cid to a string.
auto cid = charset[i - 1];
TRY(cff->add_glyph(ByteString::formatted("{}", cid), move(glyphs[i])));
} else {
auto const& name = charset_names[i - 1];
TRY(cff->add_glyph(name, move(glyphs[i])));
}
}
cff->consolidate_glyphs();