[Fontconfig] Re: [Cairo] Text API proposal

[Keith Packard]

Around 18 o'clock on Aug 11, Owen Taylor wrote:

> I don't think even linking to FreeType on, say, Windows is right; for
> various reasons:

Hmm.  I'm thinking of applications that want to generate identical results 
on every system; using different font mechanisms makes that very difficult.

One obvious such application is a cairo test suite...

> - Having cairo_font_t be polymorphic on a single system is going
>   to be confusing and lead to problems where people assume that
>   a font *must* be a cairo_font_win32_t.

Hmm.  Perhaps we don't need a 'cairo_font_win32_t'; all we really need is 
the ability to convert from an FcPattern to a windows font handle (HFONT?) 
or FT_Face.

> It isn't a bad idea to allow people to plug in a new font
> system on the fly if they are doing something really custom, but
> having two font systems always there is rather peculiar.

Hmm.  That means that cairo applications will only be portable if they use 
the trivial interface; those using lower level interfaces will need system 
specific code.  I think this means we should build an intermediate 
interface that provides enough flexibility for "reasonable" applications 
to succeed without needing operating-system specific code.  I think it 
should be possible to have an application like Mozilla run on top of the 
cairo API.

> This is an appealing choice, as long as the goals mentioned in my last
> mail are possible: consistent list of fonts with the system, and minimal
> overhead when not used.

I believe we can map fontconfig patterns to windows font selection 
structures.  Some functionality may be lost; I don't believe Windows has 
any notion of language support in the font infrastructure.

> Does this intermediate state of caring make sense? You shouldn't get one
> rasterization if you "don't care" or "really care", and a different
> rasterization if you "kind of care".

Instead of 'kinda care'/'really care', I should have said 'prefer portability'/
'prefer native fonts' -- it's a question of whether applications should be 
forced to support win32 fonts when freetype could just as easily be 
provided.

> What do you mean by an "abstract interface"?  Do you mean a generic
> interface that goes beyond being useful for don't-care applications?

Yes.  I don't want to provide a complete interface that masks the
differences between FreeType and Win32.  That seems like a bad plan...

-keith