Re: [ft-devel] ttfautohint / Oxygen / infinality

[Infinality]

Hi Vernon / Werner,

I tried it out with the version of Oxygen you sent me, with similar 
results.  I was also able to view it in Windows XP, and as I thought it 
renders fine there (although they filter the hell out of it).

1. This is the image in my original email.  The settings I'm using here 
are:  Infinality patches, native TT hinting.  (I also have a custom FIR 
filter value set on the LCD filter for all of these images)
http://www.infinality.net/files/oxygen-infinality-problems.png

2. This is what it renders like with native TT hinting if I disable all 
Infinality TT instruction tweaks:
http://www.infinality.net/files/oxygen-freetype-tt-hinting.png

3. This is what it renders like with Infinality-patched autohinting 
(which uses "slight" hinting):
http://www.infinality.net/files/oxygen-infinality-autohinting.png

You can see with #2 that it's faithfully rendering the instructions as 
you'd expect, and it looks much like standard Freetype "slight" hinting, 
which you'd also expect, since ttfautohint is creating the TT hints from 
autohint.  (The main difference between #2 and #3 is that #3 snaps 
horizontal stems to pixel boundaries, which normal Freetype slight 
hinting does not do.  I personally prefer the stems to be snapped to 
integer pixels like this.  It looks less dirty to me, however there are 
some issues with diagonal stem weights, which is a known issue since 
autohint doesn't do diagonal hinting at all.)

After experimenting around with the TT tweaks in the infinality subpixel 
hinting patches, I am able to get rid of most of the artifacts by 
turning *on* SHPIX instructions.  By default they are off in my patches 
because (my understanding is) this instruction was used historically as 
a "hack" to make outlines fit around pixels, and not much else.  (See:  
http://www.microsoft.com/typography/cleartype/truetypecleartype.aspx ).  
Is it possible to accomplish the same things that SHPIX is doing in 
ttfautohint with the more common MIRPs and such?  Not only for my 
patches, but perhaps for other device compatibility?

Thanks,
Erik


On 04/21/2012 02:07 AM, vern adams wrote:
> Many thanks for this Erik,
>
> You seem to have recreated the glitchy rendering that earlier versions of 
> ttfautohint created on iOS and when adobe apps converted ttfautohinted fonts to 
> outlines. That's very interesting i think, as it probably points to something 
> important still going on.
>
> First though i think we should check that the issue is not with a particular 
> buggy build of Oxygen; very occasionally a nightly build of an oxygen font has 
> been sent to the git repo with weird extra points that could upset ttf 
> instructions. I'll mail you some Oxygen fonts to test with and confirm that you 
> get same rendering?
>
> Many thanks
>
> vernon
>
>
>
>
> On 21 Apr 2012, at 03:15, Infinality wrote:
>
> > 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