Re: Dia, Pango, Postscript. Argh.

[Cyrille Chepelov <cyrille chepelov org>]

Le Wed, Jun 26, 2002, à 04:06:13PM -0500, Lars Clausen a écrit:

> On Wed, 26 Jun 2002, Cyrille Chepelov wrote:

> > At first, it seems [paps] embeds bitmaps into Postscript, and calls it
> > "rendering Pango text into Postscript". In fact, it does much better (not
> > as good as possible, but much better nonetheless): it uses FT to extract
> > the font outlines, and generates one (copy of) outline per instance of
> > the glyph.  It makes no attempts to compress or commonalise anything;
> > still, the resulting postscript is resolution-independent.
>
> Except that it lose all the hinting that goes into a real font and makes it
> readable at small sizes.

Is it really lost, or simply described into the
PangoGlyphString->glyphs[i].geometry structure?

> >     - we also generate custom fonts out of the outlines, using the
> > Postscript facilities. These fonts will be peculiar:
> >     * they will have funny names
> >     * they will have holes (only glyphs actually used will be embedded)
> >     * they will have a very strange encoding (or suitable concept)
>
> Why should they have other names than what the original fonts have?
> This is basically dumping the font into the file, but only with the glyphs
> that we need.

Two good reasons
        - they aren't the original fonts, since we stripped from them the
"useless" glyphs.
        - we have no clue what their original Postscript name is. If we had,
we'd just (IMO) put it and let ps2ps do the inclusion if the user wishes so.

> > We don't define a font, because that way we don't need to deal with
> > defining ligature and kerning tables and all that crap -- we extract from
> > the PangoLayout a bunch of "put this glyph -- by the way, here's the
> > definition -- at this position this scale; now put this glyph, same
> > scale, at this position; now put ...". We get rid of ps-utf8.[ch] (but
> > write something faintly similar in the long run).
>
> It seems to me this solution would create a very strange-looking PS file.
> In particular, any program trying to look for the text will find nothing.
> And again, the fonts would have their hints and stuff.  Also, optimizing
> the file with respect to a set of fonts would be impossible.  It's very
> un-postscriptlike, and I don't like it.

I don't either. That's the only solution I found. However, I disagree about
your statement that we'd loose the hints (this is handled at the Pango
shaping stage already). And on high-resolution devices (300+ dpi), I don't
think it would make much difference (but IANATypographist)

However, remember that dia 0.90 doesn't really output "text" as
understandable by the average ASCII-aware perl script. 

(on a side note, GnomePrint does use private font names. I don't know
whether it beams the whole font or only the "useful" subset)

> > I think I can manage this last approach, borrowing a lot of cod^Wideas
> > from PAPS and after reading a lot of Postscript docs on how to save an
> > path and reuse it afterwards, scaled. This should also solve the problem
> > of "my printer doesn't like my font" (in an accidental way).
>
> What happened to the idea of just dumping the font names and let ps2ps
> handle any font insertion?

Because we have no idea what this font name is (the only solution I have
involves peeking into /var/lib/defoma's cache, but I can hear the loud yells
of the RPM, InstallShield and ports-based distributions)

        -- Cyrille

-- 
Grumpf.