Re: [ft-devel] Kerning support in freetype

[Dmitry Timoshkov]

"Russell Shaw" <address@hidden> wrote:

> > I need it to implement behaviour of a win32 API GetKerningPairs, which
> > is able to return total amount of kerning pairs available. I don't see
> > why that info shouldn't be available for an application which wants to
> > cache it for any reason.
>
> If freetype has already loaded all the pairs from the file, then cacheing
> wouldn't be needed (unless you really need them all to emulate some api).

Yes, that's needed for a GetKerningPairs implementation via freetype APIs.

> > face Arial Regular has kerning
> > kerning between 32 and 65 is -2:0
> > kerning between 32 and 84 is -1:0
> > kerning between 70 and 44 is -3:0
> >
> > which is a bit small for a 1200 pixels font face.
>
> Note that your printfs are dividing by 64 (>>6).

Which is correct to convert from a 26.6 format to an integer. And
now I see my mistake thanks to James, FT_Set_Char_Size takes a 26.6
value as well, not an integer.

> > Using Win32 API GetKerningPairsW I get:
> >
> > wFirst 32, wSecond 65, iKernAmount -59
> > wFirst 32, wSecond 84, iKernAmount -19
> > wFirst 70, wSecond 44, iKernAmount -119
> >
> > which looks reasonable for a 1200 pixel sized font face.
>
> After taking out the >>6 in the printfs, i get:
>
> face Arial Regular has kerning
> kerning between 32 and 65 is -66:0
> kerning between 32 and 84 is -22:0
> kerning between 70 and 44 is -133:0
>
> using: /usr/share/fonts/truetype/msttcorefonts/arial.ttf
>
> The differences might be due to the screen resolution not
> being set in FT_Set_Char_Size().

Many thanks for the hint. In my sample if I replace

if (FT_Set_Char_Size(ft_face, 0, 1200, 0, 0))

by

if (FT_Set_Char_Size(ft_face, 0, 1200 << 6, 64, 64))

I get the closest match to what Windows returns:

face Arial Regular has kerning
kerning between 32 and 65 is -59:0
kerning between 32 and 84 is -20:0
kerning between 70 and 44 is -119:0

But using 64 as a "magic" resolution confuses. Any idea what
might cause that behaviour?

Thanks.

--
Dmitry.