Re: [ft-devel] FT_Get_Advance() docs

[Antoine Leca]

Werner LEMBERG wrote:
> 
>> I am not sure (so comment are welcome), but also I remember that a
>> property of "light rendering" was to not change the advance (i.e.,
>> enforce AF_SCALER_FLAG_NO_ADVANCE); see also
>> http://lists.nongnu.org/archive/html/freetype-devel/2008-09/msg00000.html;
>> under such a constraint/compromise, it does make sense to take the
>> quick path to compute the advances.
> 
> This is correct.  However, this condition is not carved in stone and
> might change (even if this is unlikely), thus the `fast only' test
> flag.

Okay, this makes sense. I guess we really should keep in mind this
precondition, for example by documenting it along with the revision text
about FT_ADVANCE_FLAG_FAST_ONLY (as a note over the note.)

Another thing we need to document is that the ->glyph instance inside
the face object might be erased after a call through FT_Get_Advance().


>> Does something changed on this area since September 2008?
> 
> No.  The original poster's confusion was only due to bad
> documentation, as far as I can see.

Well, there is also the "problem" that they used the FT_Get_Advance API
specifying light rendering, just to found out later that the lightly
hinted advance was actually different...


>> Also on a related point, in TrueType there is a way to get the
>> hinted advances quicker than executing the full bytecode program,
>> even if it is not alluded above: when the requested ppem has an
>> associated hdmx/VDMX table within the font.  Why it is not currently
>> available in Freetype I do not know.
> 
> Noone has requested it.  Do you volunteer to implement support for
> those two tables?

Yes, I will do that (but not today.)
I wonder also about a new demo program to check whether FT_Get_Advance()
gives, or not, the same results as FT_Load_Glyph().


>> Finally, after that whole area has been cleaned up, we should
>> revisit the FAQ:
>> http://www.freetype.org/freetype2/docs/ft2faq.html#other-bbox is out
>> of phase.
> 
> Patches please!

Will do too, now that I have the intent clear.


Antoine