[ft] Fwd: FW: Handling an embedded CID font using Freetype

[tony smith]

Thanks for the quick reply.

I've attached an example pdf file, which displays a single Chinese character.

The font details and the string in the pdf data are both readable.

The pdf string contains the single character <07F4>.

Also the relevant font has the following entry
  /CIDSystemInfo << /Registry (Adobe)/Ordering (Japan1)/Supplement 4 >>

Fontforge has a file which maps these CID values to the equivalent Unicode values.

So in this case the Chinese character is \u9AD8

But Freetype has no way to workout what the Unicode mapping is for a CFF.

So if my understanding is correct I need to uncompress the CFF file and workout the relevant mapping from the CMap information.

Thanks for you time, Tony Smith.

On 22/03/17 14:08, tony smith wrote:
> Hello
>
> I'm using Freetype to display fonts embedded in pdf data.
>
> My problem seems to be with an embedded CCF file, where the CID
> mappings is only defined in the pdf data.
> I load a Compact File Format (CFF) stream into memory.
> But when I try to select a character map, using FT_Select_CharMap, I
> get error 0x26, Invalid_CharMap_Handle.
> I've attached the CFF, font.cff, and a simple c++ program, cff.c,
> which highlights the problem.
>
> From the pdf file I know that the font is a CID one.
> So you can work out the mapping from the PDF strings to Unicode strings.
> But this information doesn't seem to be available in the CFF stream.
> So my question is how do I handle this situation?
> I can't see any way in Freetype to add the missing character encoding.
> Do I have to decompress the CFF stream, which should be a type1 font
> and then explicitly add the missing character encoding information?

CFF != compressed type 1. Although the imaging models, and many concepts are shared, they are not the same.

CFF CIDFonts don't contain any encoding information, and there is no set glyph ordering, and there is no built-in character ID to glyph index mapping (like, for example, a TTF/OTF cmap table).

To actually use a CIDFont you need to use the CMap (NOTE: not "cmap", but "CMap") specified by the PDF - that can either be custom, embedded in the PDF, or a named reference to a standard CMap (available from Adobe, but I can't remember right now where).

Parsing the CMap table will give you a mapping from character code to CID, which you can then use to pull the glyph from the font. (In Postscript terms you "compose" the CIDFont with the CMap to create a usable instance of the CIDFont).

CMaps are defined in a highly restricted variant of Postscript, so should be fairly easy to parse.

Chris

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<<attachment: winmail.dat>>

cff.pdf
Description: Adobe PDF document