Re: Pango crossplatform layout size query

[Richard Procter <richard n procter gmail com>]

On 27/03/2010, at 10:20 AM, Behdad Esfahbod wrote:

> > Should I raise a bug about this? I had assumed that identical  
> > fonts and
> > layout algorithms could (and should) guarantee identically sized  
> > layouts
> > irrespective of the underlying font rasteriser, but I don't want to
> > clutter up bugzilla with unreasonable bug reports.
>
> Well, wrong.  The rasterizers may, and typically do, return  
> different metrics
> for the same font.

Good to know.

> Your best bet is to use the FreeType backend on all
> systems.  And even then, same version of FreeType and cairo and  
> pango...

I suspected as much; thanks for confirming. As the freetype backend  
is deprecated,
though, that is not a viable option for me over the longer term (*).  
This all implies
that cairo/pango is not designed for applications that require  
invariant text extents
across platforms.

Presumably it is possible, though, as there are applications that do  
it. The
English text extents of a PDF for example are identical between OS X  
10.4
Preview and Acrobat 5.0 on an old Windows 2000 machine, despite the  
lack of
subpixel rendering on the later. SVG would also be largely useless  
for UML
diagrams (perhaps it is?) without cross-platform text extent guarantees.

For example, SVG text rendered in Firefox 3.6.2 using the same Arial  
font file
does fit nicely within the same fixed-size box across OS X 10.4 and  
Windows 2000
(at least, English text does; Hebrew and Arabic show more varied
results), whereas the width of the HTML text varies. Obviously, the  
SVG renderer
is doing something different.

I am obviously fairly ignorant about this stuff. Can anyone recommend  
a reference
for these sorts of design issues? I have read the freetype and pango  
documentation.

Lastly, if anyone has any pointers on how to layout text for UML-like  
diagrams using
cairo (via pango or something else) such that at least English text  
can be guaranteed
to stay within its box across platforms, I'd really appreciate them -  
even if it's to say
'my friend, you're a madman; that's crazy talk'.

best regards,
Richard.

*
> http://mail.gnome.org/archives/gtk-i18n-list/2008-June/msg00003.html
> "That's what the pangoft2 backend does. Check the pango_ft2_*  
> functions.
> However, I don't recommend using that backend anymore. The only  
> *supported*
> backend at this time is pangocairo, and the only one seeing future  
> development."