[HarfBuzz] How to get hb_face_t and hb_font_t without Freetype?

Behdad Esfahbod behdad at behdad.org
Fri May 24 17:49:18 UTC 2019 

Thanks Konstantin,

What about DirectWrite-driven font funcs though?  Does Qt have those?

On Fri, May 24, 2019 at 1:45 PM Konstantin Ritt <ritt.ks at gmail.com> wrote:

> Hi Behdad,
>
> That was just a glance example of the font table referencing GDI-HB bridge.
> Feel free to use it in hb-<backend> if you like it ;P
>
> As for font-funcs, I doubt GDI is a subject of interest these days. I
> might be wrong here, though.
>
> Regards,
> Konstantin
>
>
> пт, 24 мая 2019 г. в 19:18, Behdad Esfahbod <behdad at behdad.org>:
>
>> Thanks Konstantin!
>>
>> Should this become a hb-uniscribe (or hb-gdi?) API?
>>
>> On Fri, May 24, 2019 at 12:17 PM Konstantin Ritt <ritt.ks at gmail.com>
>> wrote:
>>
>>> hb_blob_t *my_reference_table(hb_face_t * /*face*/, hb_tag_t tag, void *user_data)
>>>
>>> {
>>>
>>>     HDC hdc = (HDC)user_data;
>>>
>>>     SelectObject(hdc, hfont);
>>>
>>>
>>>     char *buffer = NULL;
>>>
>>>     DWORD length = 0;
>>>
>>>         length = GetFontData(hdc, byte_swap<DWORD>(tag), 0, buffer, length);
>>>
>>>     if (length == GDI_ERROR)
>>>
>>>         return hb_blob_get_empty();
>>>
>>>
>>>     buffer = (char *)::malloc(length);
>>>
>>>     length = GetFontData(hdc, byte_swap<DWORD>(tag), 0, buffer, length);
>>>
>>>     if (length == GDI_ERROR)
>>>
>>>         length = 0;
>>>
>>>
>>>     return hb_blob_create((const char *)buffer, length, HB_MEMORY_MODE_READONLY, buffer, ::free);
>>>
>>> }
>>>
>>>
>>> hb_face_t *my_face_create_from_hdc(HDC hdc)
>>>
>>> {
>>>
>>>     return hb_face_create_for_tables(my_reference_table, (void *)hdc, NULL);
>>>
>>> }
>>>
>>>
>>>
>>>
>>> Regards,
>>> Konstantin
>>>
>>>
>>> пт, 24 мая 2019 г. в 16:39, Eli Zaretskii <eliz at gnu.org>:
>>>
>>>> > From: Ebrahim Byagowi <ebraminio at gmail.com>
>>>> > Date: Fri, 24 May 2019 20:13:43 +0430
>>>> > Cc: Harfbuzz <harfbuzz at lists.freedesktop.org>
>>>> >
>>>> > Pardon me for the may inaccurate following answer I have to write
>>>> quickly,
>>>>
>>>> Thanks for your help.
>>>>
>>>> > > Also, does HarfBuzz support TrueType Collection (TTC) files, and if
>>>> so, does it want the data only for the
>>>> > currently selected font or all
>>>> > of the data?
>>>> >
>>>> > It does, if you want harfbuzz handles it for you, you should give it
>>>> the full blob and set the index you like in
>>>> > second argument of hb_face_create, otherwise you should handle it
>>>> yourself.
>>>>
>>>> OK, this brings me to another question: what should I in general pass
>>>> as the 2nd argument of hb_face_create?  Suppose I'm using a TTF or OTF
>>>> font file, should I always pass zero as the 2nd argument?  What is the
>>>> semantics of that argument?
>>>>
>>>> > > I'm now working on the HarfBuzz font driver for Emacs on Windows
>>>> using GetFontData with the dwTable
>>>> > argument zero, to get the entire data of the font.
>>>> >
>>>> > Is it DirectWrite? Have you seen the helper we have the in
>>>> hb-directwrite.h and hb-uniscribe.h? They can be
>>>> > very useful.
>>>>
>>>> I'm not using DirectWrite, nor am I using Uniscribe.  My HarfBuzz is
>>>> built without these two, as I understand building with these back-ends
>>>> is only needed for comparison.  I want to use the HarfBuzz shaper, and
>>>> only it (Emacs already has support for Uniscribe).
>>>>
>>>> But yes, I do consult these files to figure out answers to my
>>>> questions.
>>>>
>>>> > >  does their memory need to be freed in some manner after I have the
>>>> hb_font_t object, or do I have to keep
>>>> > them as long as hb_font_t is in use?
>>>> >
>>>> > Don't free it yourself specially if in use, you can use harfbuzz
>>>> destroy callback so harfbuzz can handle it for
>>>> > you.
>>>>
>>>> Sorry, I don't think I understand: what do you mean by "harfbuzz
>>>> destroy callback"?  If you mean the 'destroy" argument of
>>>> hb_blob_create, then AFAIU this is called only to destroy user_data,
>>>> and I don't have user_data, I pass NULL as the 4th argument of
>>>> hb_blob_create.  And hb_face_create doesn't have any callback argument
>>>> at all.
>>>>
>>>> I see in the few programs in util/ that both the blob and the face are
>>>> destroyed as soon as hb_font_t object is created, which is why I
>>>> thought I could do the same.  But now you seem to say I shouldn't?
>>>>
>>>> For that matter, what should I use as the 'mode' argument of
>>>> hb_blob_create?
>>>>
>>>> This page:
>>>>
>>>>   https://harfbuzz.github.io/object-model-blobs.html
>>>>
>>>> shows an example of calling hb_blob_create with 'free' (in my case,
>>>> 'xfree') as the 'destroy' callback, so I guess my interpretation of
>>>> that argument as being pertinent to user_data was incorrect?  Still,
>>>> the questions about memory management for hb_face_t and about the
>>>> semantics of the hb_memory_mode_t enum values are left unanswered.
>>>>
>>>> > >  I see that hb_blob_create, hb_face_create etc. return empty
>>>> objects when they fail.  But I see no "is-empty"
>>>> > function or macro in the docs, did I miss something?
>>>> >
>>>> > Some of the objects may work with empty comparison but it is not
>>>> broken face
>>>> > https://github.com/harfbuzz/harfbuzz/issues/1572 but something does
>>>> it very accurately is
>>>> > hb_face_get_glyph_count
>>>>
>>>> AFAIU, you are saying that if hb_face_get_glyph_count returns zero,
>>>> the face is empty and shouldn't be used, is that right?
>>>>
>>>> > > Where do those 64.0 factors come from?
>>>> >
>>>> > Subpixel accuracy, harfbuzz works with integers but as subpixel
>>>> accuracy needed you have to we need to do
>>>> > some scaling. Scaling is not the pixels but _set_ppem and _set_ptem
>>>> is (this is very inaccurate, but I hope
>>>> > would be useful)
>>>>
>>>> Does this mean I should use the factor of 64 in my code as well?  Or
>>>> does that value depend on some properties of the font?
>>>>
>>>> >
>>>> > > Or point me to the documentation where that is described, if I
>>>> missed it?
>>>> >
>>>> > https://harfbuzz.github.io/ may address some of your issues
>>>>
>>>> Thanks again for your help.
>>>> _______________________________________________
>>>> HarfBuzz mailing list
>>>> HarfBuzz at lists.freedesktop.org
>>>> https://lists.freedesktop.org/mailman/listinfo/harfbuzz
>>>
>>> _______________________________________________
>>> HarfBuzz mailing list
>>> HarfBuzz at lists.freedesktop.org
>>> https://lists.freedesktop.org/mailman/listinfo/harfbuzz
>>
>>
>>
>> --
>> behdad
>> http://behdad.org/
>>
>

-- 
behdad
http://behdad.org/
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