Re: WOFF-ACTION-196: Review treatment of empty glyphs vs 0-contour glyphs

Sorry, by "rejecting glyphs" I had in mind the result would be rejecting
the whole font (as we don't really have a way to reject just part of it) if
it had glyphs with bounding boxes for 0 contours. I probably should have
actually stated that in full.

Zeroing out the BB for glyphs with 0 contours strikes me as viable if we
are certain such a BB is just an error on the part of the creator or the
tool the creator used. If we can't be sure of that then I would think we
should just reject such fonts.

On Thu, Feb 18, 2016 at 9:16 AM, Levantovsky, Vladimir <
Vladimir.Levantovsky@monotype.com> wrote:

> Rod wrote:
>
> > I'm OK with just rejecting glyphs with bounding boxes for 0 contours.
>
> It is a possibility but when I considered different options (such as
> attempting to fix a font instead of rejecting it outright) my preference
> was to simply reject a whole font – we don’t do (or require doing) an
> exhaustive font validation prior to encoding so if you see something funny
> happening in one portion of a font there is a risk that there may be
> something else we missed. Rejecting it as junk seems like a safe bet.
>
>
>
> > Another option might be to require encoder to zero out BB for glyphs
> with 0 contours.
>
> This is in essence what we started with. By requiring the encoder to clear
> the bbox flag for both empty and 0-contour glyphs we’d force the decoder to
> reconstruct the empty glyph in both cases. It is a viable option but, like
> I mentioned earlier, I am not sure it the approach to fix a problem you see
> (and knowing you may’ve missed something you didn’t see) is a good idea –
> what if the ‘irregularities’ of the font data is an indication of the
> malicious intent. So again, it’s really about a general approach of whether
> we should be trying to fix what we can (and miss out on what we didn’t see)
> or reject a font if it has “funny data”.
>
>
>
> Thank you,
>
> Vlad
>
>
>
>
>
> *From:* Roderick Sheeter [mailto:rsheeter@google.com]
> *Sent:* Wednesday, February 17, 2016 6:30 PM
> *To:* Levantovsky, Vladimir
> *Cc:* WebFonts Working Group
> *Subject:* Re: WOFF-ACTION-196: Review treatment of empty glyphs vs
> 0-contour glyphs
>
>
>
> I'm OK with just rejecting glyphs with bounding boxes for 0 contours.
> Another option might be to require encoder to zero out BB for glyphs with 0
> contours.
>
>
>
> On Tue, Feb 16, 2016 at 1:18 PM, Levantovsky, Vladimir <
> Vladimir.Levantovsky@monotype.com> wrote:
>
> Folks,
>
> After spending some time musing on the subject matter I decided it might
> be a good idea (but you be the judge) to at least mention the degenerate
> case of "glyph with zero outlines" in the spec. One thing leads to another
> and I ended up adding a new conformance test case where an authoring tool
> would have to check that glyph with zero contours has no bounding box (i.e.
> all values are zeros) and reject the input font if this is not the case.
> (see http://dev.w3.org/webfonts/WOFF2/spec/#conform-mustRejectNonEmptyBBox
> )
> Once this check is performed, the existing test case (
> http://dev.w3.org/webfonts/WOFF2/spec/#conform-mustClearEmptyBBox) is now
> extended to cover both empty glyph records and glyphs with zero contours.
>
> I realize that having a glyph record with zero contours is highly unlikely
> (but not impossible) so having the spec mention both cases would be
> justified, if only to prevent an uncertainty associated with the undefined
> cases and possible malicious content.
> Comments?
> (Once I hear you say "Yeah, let's keep this in the spec", my next step
> would be to come up with the test descriptions for both cases.)
>
> On a separate issue regarding our scheduled telcon tomorrow - any progress
> to talk about? Considering that some folks are on vacation this week and
> the low level of WG activities that require group discussions - should we
> cancel the call tomorrow and postpone it until March 2nd? (Reminder - I
> will be traveling next week.)
>
> Thank you,
> Vlad
>
>
>
> -----Original Message-----
> From: WebFonts Working Group Issue Tracker [mailto:sysbot+tracker@w3.org]
> Sent: Wednesday, February 10, 2016 4:44 PM
> To: public-webfonts-wg@w3.org
> Subject: WOFF-ACTION-196: Review treatment of empty glyphs vs 0-contour
> glyphs
>
> WOFF-ACTION-196: Review treatment of empty glyphs vs 0-contour glyphs
>
> http://www.w3.org/Fonts/WG/track/actions/196
>
> Assigned to: Vladimir Levantovsky
>
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