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From: Bill McClain <wmcclain@salamander.com>
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Subject: Re: more on missing ligatures
Date: Mon, 11 Mar 2002 07:29:34 -0600
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Hans Hagen wrote:

> Now, tex itself only needs the tfm file but dvips and the pdftex backend
> need the vf file in order to construct composed or manipulated glyphs. So,
> when vf was introduced, tex was not adapted, but dvips was,
> 
> I must admit that this model is not that clear -)

Ah! I think I see it now. This means the examples on my help page were
wrong also; I was referencing raw files when I shouldn't have. I've
corrected that now.

To summarize:

My mistake was thinking that the font names used in a tex job had to be
those listed in the map file. (And this happened to be true in my early
tests because the fonts I was using were not virtual). But, as you point
out, the map file is for the backend: associating a tfm file with the
glyph repository (pfb).

Tex (I have just learned), given a font name, searches in the usual font
places for a tfm file. Magically, it knows when a tfm has virtual vf
file of the same name. The vf file contains references to other tfm or
vf files. Eventually, when the backend runs, it needs the mapping from a
tfm to a pfb.

Using a real example:

Texfont produced for me:

    texmf/fonts/tfm/adobe/sabon/texnansi-raw-sar.tfm
    texmf/fonts/tfm/adobe/sabon/texnansi-sar.tfm

    texmf/fonts/vf/adobe/sabon/texnansi-sar.tfm

and a map file which contains:

    texnansi-raw-sar Sabon-Roman 4 < sar_____.pfb texnansi.enc

In my setup for this font, I use:

    \definefontsynonym[Sabon-Roman][texnansi-sar][encoding=texnansi]

Tex finds and uses the virtual font, which has the ligature info (the
raw file doesn't!)

The virtual font has a link to the raw font:

    vftovp texnansi-sar | grep FONTNAME
        (FONTNAME texnansi-raw-sar)

When the backend needs to generate the glyphs, it uses the
texnansi-raw-sar entry in the map file to find the pfb and encoding.

Simple, eh? (Honestly, bundling resources together has been a problem on
many systems I have used. Anyone ever program the Macintosh?)

-Bill