[ft-devel] ttfautohint / Oxygen / infinality

[Infinality]

Hi guys,

Today I tested out the TT-instructed Oxygen font from the KDE repo with 
my TT subpixel hinting patches.  This is the result:
http://www.infinality.net/files/oxygen-infinality-problems.png

Yikes!!!  After examining the TT instructions in the instructed version 
of the Oxygen fonts, it looks like the way that ttfautohint is 
generating instructions is substantially different than typical 
TT-instructed fonts.  Since my patches are attempting to do what the MS 
rasterizer does (at least with legacy fonts), I'm curious how these 
render on Windows.  Unfortunately I don't have a Windows system 
available to test that on at the moment, however my guess is that it 
renders just fine on Windows.

I have a way to exclude certain fonts or individual glyphs within a font 
from using the tweaks that my patches employ (i.e. render it the way 
Freetype TT hinter does by default), but I'd rather not build up a giant 
hard-coded exclusion list of fonts generated by ttfautohint if at all 
possible.  And, given that the TT subpixel hinting patches may soon land 
into Freetype, I'd like make them work nicely with other 
Freetype-related software.  :D   So, I'd like to adapt my TT hinting 
patches to gracefully handle fonts that have been hinted with ttfautohint.

My question is this:  Is there something unique about ttfautohint-ed 
fonts that indicates they are already taking into account 
subpixel-hinting?  I know there is the "ready for Cleartype" flag, but 
it never seems to be set in any fonts I've seen (including Oxygen), even 
the MS ones.  Also, the Microsoft Cleartype fonts seem to behave well 
with my patches just as they are.  They are designed for 
Cleartype/subpixel just as the ttfautohint fonts are.  I guess I'm 
trying to reconcile what exactly ttfautohint is doing differently that 
causes these issues.  Can any of you provide any insight?

Thanks,
Erik / Infinality