Re: [ft] Freetype 2.4.4 -> freetype 2.4.12: FT_Get_Advance changed behaviour?

[Gregor Mückl]

On 6/3/2013 9:05 AM, Werner LEMBERG wrote:
> > I've reduced my code to the attached program (which is still a bit
> > convoluted - sorry!).  [...]
>
> Thanks.  There was a serious bug in FT_Get_Advance which has been
> fixed in version 2.4.9: According to the documentation, the returned
> advance value is either in 16.16 format or in font units.  Before the
> fix this was true only if it was possible to quickly retrieve the
> advance value, which is not the case for hinted TT fonts.  You
> probably hadn't noticed that you circumvented the bug by using the
> 26.6 format, together with undoing the wrong double scaling,
> right? :-)
>
> The fix is rather simple (see below) if you want to stay with
> computing everything in 26.6 format.
>
>
>      Werner

Thank you very much for looking into this! The suggested fix works 
nicely. I vaguely recall that I was fiddling with this scaling when I 
originally wrote this code because it was behaving wrong in *some* way. 
But I must have been very tired to not figure out that something was 
amiss here :).

I looked at the documentation for FT_Get_Advance again. I'm using 
FT_LOAD_DEFAULT as flags, but the return value is in a 16.16 scaling. 
Yet, the documentation states:

"By default, the unhinted advance is returned in font units."

To me, this reads like a (probably unwanted) contradiction to the actual 
behaviour. I suggest something like the following instead:


"The returned advance depends on whether scaling is performed (based on 
the value of flags). If scaling is performed, the advance is in 16.16 
format. Otherwise, it is in font units."

Regards,
Gregor