[cairo] OpenType font variations and cairo

[Behdad Esfahbod]

On Fri, Sep 15, 2017 at 3:51 AM, Adrian Johnson <ajohnson at redneon.com>
wrote:

> On 15/09/17 09:29, Matthias Clasen wrote:
> > On Thu, Sep 14, 2017 at 5:54 PM, Adrian Johnson <ajohnson at redneon.com
> > <mailto:ajohnson at redneon.com>> wrote:
> >
> >     On 15/09/17 05:52, Matthias Clasen wrote:
> >     > On Thu, Sep 14, 2017 at 12:37 PM, Behdad Esfahbod
> >     > <behdad.esfahbod at gmail.com <mailto:behdad.esfahbod at gmail.com>
> >     <mailto:behdad.esfahbod at gmail.com
> >     <mailto:behdad.esfahbod at gmail.com>>> wrote:
> >     >
> >     >     Thanks Matthias.  I took a look at the patch.  Looks good!
> Minor
> >     >     comments:
> >     >
> >     >     - Moving the format towards CSS by default (no comma, no equal
> sign;
> >     >     just spaces!) while accepting both is what I do in HarfBuzz.
> Maybe
> >     >     advertise the same here,  UPDATE: I was wrong.  CSS uses comma
> as
> >     >     well.  It's the equal sign that they don't use, they use
> space.  We
> >     >     should accept both.
> >     >
> >     >
> >     > I've made the parser a bit more flexible. It now accepts
> variations like
> >     >
> >     > wdth=200,wght=300
> >     > wdth 200, wght=300
> >     > wdth 200 , wght 300
> >
> >     Does it work with decimal commas?
> >
> >
> > The patch currently uses strtod, so yes, it will parse floating point
> > numbers, but decimal separators spell trouble.
> > I could rewrite it to use strtod_l, if that is ok to use in cairo.
>
> So what happens on platforms where strtod_l is not available?
>

Then parsing fails.  But then again, this is only hooked up in the FreeType
backend right now...


> The function decode_real() in cairo-cff-subset.c has code for locale
> independent parsing of floating-point numbers. Maybe that could be
> factored out into separate function and reused.
>

Sounds good.

Where is the variations text string normally expected to come from? I
> can see the code reading the FC_FONT_VARIATIONS property but I can't
> find this in the current fontconfig git. Where is this documented?
>

I have a branch that adds that.  I'll finish it today or tomorrow and
post.  You can wait till then.

Is the text string supplied to cairo_font_options_set_variations()
> likely to be generated by sprintf or is it always read from an external
> source in C locale format?
>
> We really need a test case for this. It is hard to review code I can't
> test.
>

In a day or two I'll have cairo piece hooked-up in hb-view, and then cairo
and fontconfig bits in pango-view.  That should simplify testing.

-- 
behdad
http://behdad.org/
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