Re: A DVI viewer with freetype2

[David Turner]

Hi,

> sx0005> There never will be a `CJK module' for freetype2.  VFlib provides an
> sx0005> additional layer to support CJK subfonts as needed by TeX.
> 
> For example, 'font metric adjuster font driver'.
> It obtains a glyph from another font driver and modifies font metrics.
> It is very important for handling Japanese Kanji characters...
> (In VFlib, 'a font' does not mean a font file...)
> 
It certainly isn't a good idea to put this kind of processing inside
FreeType 2, which is all about providing information contained in
font files.

glyph metrics are typically managed and cached by a higher level API,
this allows a lot of other things that would complexify FT2 if included
in the library, like style synthesis, virtual fonts, font subsets, etc..

> If you want to develop a DVI driver with FT2,
> you need to obtain design size of a font from TFM font (TrueType and Type1
> format do not contain such information).

If there is a specific font format for DVIs, you can add a driver to
load them, and eventually read the metrics from the TFM file (a bit
like the Type 1 driver is able to read data from an AFM file).

However, if a TFM is essentially an application-centric file, it's
processing is better left to the DVI Viewer or the high-level API.

> Then obtain a bitmap of a chracter accoring to design size, device
> resolution, and maginification factor in DVI file.
> It is not a difficult task.
> 
> But your DVI driver is very limited: only TrueType and Type 1 are
> supported.  Unfortunately, some fonts do not offered in Type1 format...
> So, that will be a problem for you.
> To solve the problem, I believe you must write a code like VFlib.
> 
We can add code to support more font formats within FT2, like HBF, and
we can also add code for a high-level API on top of it, but the things must
remain distinct.

> sx0005> As said above VFlib provides some more functionality, especially for
> sx0005> CJK fonts) which should not be in FT2.
> 
> Some CJK character fonts are in special bitmap format (not PK, not GF)
> and we need a mechaism (like VFlib) to use such fonts in TeX.
> In addition, character code conversion is also important for CJK fonts...
> 
> VFlib is designed not for a simple set of multiple font drivers;
> its higher layer is imprtant point.
> 

Exactly, it has many features that will never be part of FT2 itself.
Something like a "FreeType Text Service" was hinted, but let's wait
for the release of FT2 :o)

- David

> -- h.kakugawa
> (a developer of VFlib)