Re: Pango crossplatform layout size query

[Behdad Esfahbod <behdad behdad org>]

On 03/24/2010 11:05 PM, Richard Procter wrote:
> Hi Behdad,

Hi,

I saw your mail on the gtk-i18n-list.  Didn't reply because I didn't have
immediate insight to add.  Anyway, CC'ing the list again.  Please keep the
discussion there.


> I've found that identical pango layouts using (what I have tried to
> ensure are) the same absolute sized font have different extents across
> platforms (OS X & win32).
> 
> 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.  Your best bet is to use the FreeType backend on all
systems.  And even then, same version of FreeType and cairo and pango...


> If it is a legitimate bug, I would happy to work on it myself if I had
> an idea of what I was commiting myself to upfront - do you have a
> feeling for how much effort a fix would involve?

Fixing this is a rather large task.  Requires restructuring the
cairo-scaled-font layer, and making sure all three backends (FreeType, Win32,
OS X) respect the cairo_font_options_t like CAIRO_HINT_METRICS_OFF.  Even
then, there's no guarantee.

behdad

> If you have any questions please don't hesitate to ask,
> 
> best regards,
> Richard.