[cairo] UserFontFace vs FtFontFace management (cairomm)

[Jonathon Jongsma]

On 12/03/2008 01:49 PM, Behdad Esfahbod wrote:
>> Perhaps there's a better way to design that interface, but as you can
>> see the idea was simply to pass the glyphs as a vector (array).  So with
>> this interface the user has no way to return a negative value for
>> num_glyphs -- std::vector::size() maps to num_glyphs, and the size of an
>> array is always non-negative.  So in order to provide a default
>> implementation for this virtual function that returned a -1 for
>> num_glyphs, It seems that I would either have to revert to using C-style
>> arrays, or I would need to add an additional sentinal argument to the
>> cairomm interface (e.g. 'bool&  call_unicode_to_glyphs_instead' :).
>> Neither of these options seem especially satisfying to me.
>
> The C interface is now written in stone.  What we can do is to add a special
> cairo_status_t value for this case that will be interpreted as UNIMPLEMENTED
> only when used in this context.  That's possible if you don't find any other
> solutions.
>
> behdad


OK, so I think I've found an acceptable workaround for this.  In 
essence, my default text_to_glyphs virtual function sets a flag in the C 
object's user_data, and if that user_data flag is set, I pass a negative 
value back for num_glyphs.  So this workaround seems acceptable for my 
'internal' use, but there's no way for a user to do the same thing 
(since I don't expose the user_data key for that flag, etc).  And since 
I don't have any experience with advanced text stuff, I need some advice 
whether this is OK or not.  Is it reasonable for a user to implement 
both of these methods and want to use text_to_glyphs in some 
circumstances and unicode_to_glyph in other circumstances (in other 
words, in a C implementation, register both callbacks and sometimes 
return -1 for num_glyphs and sometimes return actual glyphs)?  Or for a 
given UserFont, is a user *always* going to use either one or the other?

jonner