Re: Pango: Accessing x-height/mean-line in Pango layout

[Behdad Esfahbod <behdad behdad org>]

On 12-12-19 05:43 AM, Olivier Fourdan wrote:
> 
>>> Looking at typefaces definitions here [1] and [2], the positioning should be
>>> ideally made based in between the baseline and the mean-line (baseline -
>>> x-height).
>>>
>>> I wonder, how can I access the x-height (or better the meanline) using the
>>> Pango API? Is there a simple API for this?
>> Not directly.  If you are using pangofc, you can obtain the FT_Face from the
>> PangoFont, then get the (I think) "OS/2" table of the font, and get the
>> x-height from in there.
> 
> Humm, that sounds quite complicated and platform specific, no?

Right.  For better or worse, Pango doesn't expose x-height.  Which is not that
bad when you consider that "x-height" makes little sense for most scripts
other than Latin/Greek/Cyrillic..


> So I took another approach to the problem.
> 
> Assuming Pango rightfully places the strikethrough, I retrieved the position
> of the strikethrough with something like:
> 
>     context = pango_layout_get_context (layout);
>     language = pango_language_get_default ();
>     desc = pango_layout_get_font_description (layout);
>     metrics = pango_context_get_metrics (context, desc, language);
> 
>     baseline = pango_layout_get_baseline(layout);
>     strikethrough =  pango_font_metrics_get_strikethrough_position (metrics);
>     thickness =  pango_font_metrics_get_underline_thickness (metrics);
> 
>     return PANGO_PIXELS(baseline - strikethrough - thickness / 2);
> 
> And that gives (what I believe is) an acceptable result, at least from my
> point of view.

Sounds reasonable.

behdad

> Cheers,
> Olivier
> 

-- 
behdad
http://behdad.org/