Re: [ft-devel] Regression issue - CFF

[Chris Liddell]

This looks very much like a winding-rule issue. Despite Adobe's font 
documentation claiming that glyphs should be rendered with non-zero 
winding, the Adobe *font* scalers/renderers actually use even-odd.

This can be seen in CPSI (if anyone has access to it), by drawing a 
series of glyphs like the one in this example getting larger and larger.

They will start rendering as intended (with the bowl "hollow") whilst 
the font renderer is rendering them into the glyph cache. At some point, 
the glyph gets too large to cache, and the glyph is converted to path, 
and rendered by the "normal" line-art rendering code, using a normal 
fill operation - which is non-zero winding, and glyph ends up drawn as 
Freetype does (with the "bowl" filled).

We (Ghostscript) also have an example of a font with at least one glyph 
like this.

In my experience, most other PS/PDF products that implement their own 
font rendering have also adopted the even-odd rule, for obvious reasons: 
a well formed glyph, that follows the spec will render correctly with 
either non-zero or even-odd, badly formed glyphs, like this example, 
will still render as intended (although, arguable, not "correctly").


I've been periodically looking at revising the Freetype monochrome scan 
conversion code to optionally support even-odd, but I really haven't 
been able to dedicate the time to it to really make headway. (I believe, 
from the comments, that the grayscale renderer already supports even-odd).

If this looks like becoming more important, and no one else is up for 
it, I can try to focus more time on the task.....

Chris


On 08/08/12 04:02, suzuki toshiya wrote:
> I reproduced this issue by 2.4.6, 2.3.12, 2.3.0.
> Although it would be an issue, I think this is NOT regression.
>
> Regards,
> mpsuzuki
>
> Ivan Nincic wrote:
> > Hello Werner,
> >
> > FYI: I ran into a discrepancy between how FT (latest) and Acrobat render
> > some CFF fonts.
> > It seem that the error is cause due to interpretation of the fill rule (even
> > odd vs. winding) or something like that.
> >
> > The font file was generated with Adobe PaperCapture.
> >
> > IvanN
> >
> >
> > -----Original Message-----
> > From: Ivan Nincic [mailto:address@hidden
> > Sent: Friday, April 13, 2012 10:50 AM
> > To: 'address@hidden'
> > Cc: 'address@hidden'; 'address@hidden'
> > Subject: Regression issue - CFF
> >
> > Hello Werner,
> >
> > FYI: I run into a regression issue with the latest FT (trunk) version.
> > Attached is a sample font. I don't claim that this is a valid font however
> > FT was able to render the file in 2.4.4 but not in 2.4.9.
> >
> > IvanN
> >
> >
> > ------------------------------------------------------------------------
> >
> > _______________________________________________
> > Freetype-devel mailing list
> > address@hidden
> > https://lists.nongnu.org/mailman/listinfo/freetype-devel
>
>
> _______________________________________________
> Freetype-devel mailing list
> address@hidden
> https://lists.nongnu.org/mailman/listinfo/freetype-devel