Re: [Devel] FreeType 2.1.x rejects CMap4 of certain Dyna-Fonts [patch by akito]

[David Turner]

Hello Anthony,

Anthony Fok wrote:
> Dear all,
>
> There has been a series of patches made by Akito Hirai of the Japan KDE
> User's Group, and recently by Firefly in Taiwan, to improve CJK font
> rendering with FreeType, fontconfig/Xft2, Qt, Pango and Mozilla. 
> Perhaps due to the language barrier, or perhaps due to unfamiliarity
> with upstream mailing lists, these patches have not made their way
> upstream yet.  Anyhow, let's get started!  ;-)
Excellent news :-)

> So, let's start with FreeType-2.1.4.  Due to another CMap4 bug in many
> Dyna CJK fonts, FreeType 2.1.x rejects their Unicode CMap, rendering
> these fonts unusable.  Akito-san has provided a patch to deal with
> buggy Dyna Japanese fonts.  Firefly and other Taiwan KDE users have
> verified that buggy Dyna Chinese fonts became usable with this patch. 
> So, please apply the attached patch.  This patch is also available
> here:
>
>     http://www.kde.gr.jp/~akito/patch/freetype2/freetype-2.1.3-ttcmap4.patch
>
> It applies cleanly to 2.1.4 too.
OK, I see no reason not to apply it to the current code, it seems simple
and clean.

> David, Akito-san also worked on the autohinter to make it hint CJK
> fonts well too, and released a patch last week (updated 2003-04-16).  
> Firefly has also verified it and find it marvellous.
>
>     Before:   http://www.kde.gr.jp/~akito/patch/image/ah-slight1.png
>     After:    http://www.kde.gr.jp/~akito/patch/image/ah-slight2.png
>     Patches:  http://www.kde.gr.jp/~akito/patch/freetype2/2.1.4/
>
> It would be marvellous if you could look into it.  Thanks in advance!

That's impressive, but the patch is so incredibly large that we're not
going to apply it directly without carefully reading and understanding
it. After a quick look at it, it seems that the current code may have
some performance issues because it calls FT_Get_Char_Index in a very
large loop to determine wether certain Unicode ranges are supported.

There probably is a way to dramatically speed this using
"FT_Get_First_Char" and "FT_Get_Next_Char", and I'll look to it.

It also seems that this patch modifies the hinting of non-CJK fonts as
well, which means that we need to perform a lot of testing to check that
it doesn't degrade some other popular fonts...

Again, more study to be done...

Thanks a lot,

- David Turner
- The FreeType Project  (www.freetype.org)


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