[vlc-devel] [RFC PATCH] freetype: using Pango for text layout

[Jean-Baptiste Kempf]

On 21 Jan, Salah-Eddin Shaban wrote :
> > It can take HTML-like or raw text, and display it.
> > And it supports many quirks with teletext and all. Including some
> > japanese half-glyphs.
> >
> > Therefore this module parses the HTML/XML, then tries to render it using
> > freetype.
> > But that means that modules like QuartzText or DirectWrite, (or any
> > other) does not support the same set.
> 
> Right. That's why I felt better working on the same module than on a
> separate one. And that's why I had to go with PangoFT.

I got that :)

> > Now what?
> > ---------
> > There are several path of actions, from now on...
> > 1) improve the FT module until it gets to Theory, and probably merge
> >    harfbuzz library in it.
> > 2) create on API above libass so we can send text_style_t, and not only
> >    ASS style
> > 3) create a new pango module for Unixes
> > 4) mplayer way: Transform all text into SSA and send to libass
> >
> > 1) Difficult, but more portable and safe, for regressions
> > 2) Should be simpler, but question about merging in libass arises.
> >    However, libass supports everything, including correct fallback
> >    (well, almost, still fontconfig on Windows...)
> >    So this is probably a libass fork
> > 3) Well, less portable, for iOS, Windows and Android.
> > 4) not sure it's the best idea, perf wise...
> >
> 
> Thanks for the detailed explanation. I'll probably look into the first
> option for starters. According to one of the developers of Pango and
> HarfBuzz, HarfBuzz only supports the shaping part of the process, and
> we have to do the itemizing part manually. The line breaking part is
> already there in the freetype module it just has to take into account
> RTL text.

I think this is correct.

> http://mces.blogspot.in/2009/11/pango-vs-harfbuzz.html

See http://behdad.org/text/

> One last thing. As far as I know, Qt's QTextLayout performs the same
> operations that Pango does. Do you think we could use it here? It
> should be simpler than using HarfBuzz directly. Does Qt have any
> issues on certain platforms?

This is basically the same issue.
Qt will probably never fly on our version of VLC for Android, iOS or
OSX.

As for complete portable text layouts, I know
 - gtk (pango)
 - Qt
 - libass
 - our own? (lol)
 - webbrowsers

With my kindest regards,

-- 
Jean-Baptiste Kempf
http://www.jbkempf.com/ - +33 672 704 734
Sent from my Electronic Device