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

Konstantin Ritt ritt.ks at gmail.com
Fri May 24 17:58:10 UTC 2019 

пт, 24 мая 2019 г. в 20:49, Behdad Esfahbod <behdad at behdad.org>:

> Thanks Konstantin,
>
> What about DirectWrite-driven font funcs though?  Does Qt have those?
>

Yep we do, both GDI and DW.
I think we should start moving our backends (or their respective parts) to
HB at some point. We could start a dedicated topic to discuss that.


Regards,
Konstantin




>
> 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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