[HarfBuzz] How to override Harfbuzz's freetype functions?

[Deron Kazmaier]

Thanks for the deeper details. The example code I've looked at (pango 
and firefox) do not use the unset call. I know your time is limited, and 
I appreciate the info.

Deron


On 2/1/11 12:03 PM, Behdad Esfahbod wrote:
> On 02/01/11 09:56, Tom Hacohen wrote:
>> Dear all,
>>
>> I ran a test application in callgrind and noticed that the calls to
>> FT_Load_Glyph are what slows everything down. We already have glyph
>> cache in EFL and I would really like to be able to use it with harfbuzz.
>> At first glance, it seems like I can't override harfbuzz's
>> hb_ft_get_glyph_advance from the outside, but I have to implement my own
>> class and put it in harfbuzz, which is less than convinient.
> The way this is supposed to work is that you create your own font callbacks
> that *wrap* the original ones.  You
>
>    hb_font_funcs_t *new_funcs, *orig_funcs;
>    hb_destroy_func_t orig_destroy;
>    void *orig_user_data;
>
>    new_funcs = hb_font_funcs_create ();
>
>    /* set funcs in new_funcs */
>
>    hb_font_unset_funcs (font,&orig_funcs,&orig_destroy,&orig_user_data);
>
>    /* save orig_funcs, orig_destroy, and orig_user_data in new_user_data */
>
>    hb_font_set_funcs (font, new_funcs, new_user_data, new_destroy);
>
>
> Then in your callbacks, you can use orig_funcs and orig_user_data to call into
> harfbuzz to get the value, and cache it.
>
>
> I'm not quite satisfied with this scheme.  The problem with it is that if/when
> new callbacks are added to hb_font_funcs_t, your code needs to be updated to
> relay those.  Would have been much nicer if they falled through automatically
> (so you could in essence really subclass a font_funcs_t).  I'll think more
> about it to see if I can make that happen.
>
> behdad
>
>
>> I'd very much like to be able to do that, because using my cache will
>> make everything a lot faster.
>>
>> Are my observations correct?
>>
>> How do you guys (that use harfbuzz in other projects) solve it?
>>
>> Thanks,
>> Tom.
>>
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>>
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