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Re: [ft-devel] Regression issue - CFF

From: Chris Liddell
Subject: Re: [ft-devel] Regression issue - CFF
Date: Wed, 08 Aug 2012 08:27:00 +0100
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:14.0) Gecko/20120714 Thunderbird/14.0

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.....


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.


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.


-----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.



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