Re: ISSUE-283 (Deterministic Presentation): Deterministic text wrapping and presentation [TTML2]

On Thu, Oct 10, 2013 at 9:23 PM, Pierre-Anthony Lemieux <pal@sandflow.com>wrote:

> Hi Glenn,
>
> Thanks for the feedback.
>
> > without a standard line breaking algorithm
>
> Ah. What options exist?
>

UAX #14 [1], implemented by ICU. We actually have a feature for this in
TTML, #lineBreak-uax14

and say the following
9.4 Line Layout

If a profile that applies to a *Document Instance* requires use of the
#lineBreak-uax14<http://www.w3.org/TR/2013/REC-ttml1-20130924/#feature-lineBreak-uax14>
feature
(i.e., the value attribute for the feature is specified as use), then the
recommendations defined by Line Breaking
Algorithm<http://www.unicode.org/reports/tr14/#Algorithm>
 [UAX14] <http://www.w3.org/TR/2013/REC-ttml1-20130924/#uax14> apply when
performing line layout on the content of the *Document Instance*.
[1] http://www.unicode.org/reports/tr14/


>
> Best,
>
> -- Pierre
>
>
>
> On Thu, Oct 10, 2013 at 7:04 PM, Glenn Adams <glenn@skynav.com> wrote:
> > It is a weak version of OPTION 2, without a standard line breaking
> > algorithm. Further, there is no way in an XSL-FO or CSS mapping to say
> the
> > rendering engine that font Y should be used with the metrics of font X.
> So I
> > suspect that any OWP based presentation processor would simply ignore
> that
> > requirement.
> >
> >
> > On Thu, Oct 10, 2013 at 7:48 PM, Pierre-Anthony Lemieux <
> pal@sandflow.com>
> > wrote:
> >>
> >> Hi Glenn et al.,
> >>
> >> > OPTION 2 - Difficult to specify concrete collection of fonts that
> serves
> >> > all of Unicode,
> >> > or at least the subset of Unicode used in regional caption/subtitle
> >> > text.
> >>
> >> The IMSC draft uses ubiquitous fonts (Courier and Helvetica) to define
> >> specify reference font metrics for selected font families
> >> (monospaceSerif and proportionalSansSerif, respectively). Presentation
> >> processors are not required to render using the reference font (and
> >> can use a font of a different shape in fact), but must render using
> >> the font metrics of the reference font.
> >>
> >> Is that OPTION 2, or a new OPTION 5?
> >>
> >> Best,
> >>
> >> -- Pierre
> >>
> >> On Thu, Oct 10, 2013 at 12:52 PM, Glenn Adams <glenn@skynav.com> wrote:
> >> > We have discussed this many times in the past, going back to 2003, and
> >> > within CSS and XSL WGs, where it is similarly a known problem.
> >> >
> >> > The only way to obtain interoperable deterministic line breaks is:
> >> >
> >> > OPTION 1 to manually break the line using <br/> and specify
> >> > wrapOption='noWrap'
> >> >
> >> > or
> >> >
> >> > OPTION 2 require every presentation processor to support at least one
> >> > concretely specified font, with effectively identical metrics on every
> >> > platform, *and* require every presentation processor to support at
> least
> >> > one
> >> > concrete line break implementation, with a way for the author to
> express
> >> > that algorithm must be used;
> >> >
> >> > or
> >> >
> >> > OPTION 3 require support for downloadable fonts and at least one
> >> > specifiable, universally supported line break implementation;
> >> >
> >> > or
> >> >
> >> > OPTION 4 use only image based captions, where rendering is done once
> >> > during
> >> > authoring.
> >> >
> >> > Comments
> >> >
> >> > OPTION 1 - May lead to region overflow (and possible clipping)
> >> > OPTION 2 - Difficult to specify concrete collection of fonts that
> serves
> >> > all
> >> > of Unicode, or at least the subset of Unicode used in regional
> >> > caption/subtitle text.
> >> > OPTION 3 - Probably best option in theory, most likely solution would
> >> > require support for (1) OpenType fonts delivered by WOFF, (2) freetype
> >> > font
> >> > rasterizer, and (3) ICU implementation of UAX14.
> >> > OPTION 4 - Makes timed "text" rather pointless, unless both image and
> >> > text
> >> > formats delivered together.
> >> >
> >> >
> >> > On Thu, Oct 10, 2013 at 11:31 AM, Timed Text Working Group Issue
> Tracker
> >> > <sysbot+tracker@w3.org> wrote:
> >> >>
> >> >> ISSUE-283 (Deterministic Presentation): Deterministic text wrapping
> and
> >> >> presentation [TTML2]
> >> >>
> >> >> http://www.w3.org/AudioVideo/TT/tracker/issues/283
> >> >>
> >> >> Raised by: Nigel Megitt
> >> >> On product: TTML2
> >> >>
> >> >> There's a complex interaction between lineHeight, fontSize, overflow
> >> >> and
> >> >> wrapOption that determines, for the font that the display processor
> >> >> chooses,
> >> >> how much text will fit on a line and whether any text that doesn't
> fit
> >> >> overflows or is truncated. This creates a problem for document
> authors
> >> >> if
> >> >> they can not be certain of the metrics of the font used to present
> >> >> their
> >> >> content.
> >> >>
> >> >> The goal from an audience perspective is that the on-screen text is
> >> >> readable and complete. Nobody wants missing words (that could change
> >> >> the
> >> >> editorial meaning) or text that is visible but unreadable.
> >> >>
> >> >> TTML offers little by way of solution to this real world problem at
> the
> >> >> moment. The IMSC submission presents a 'reference font' mechanism,
> >> >> which
> >> >> should be considered. Is there anything more that we can do natively
> in
> >> >> TTML
> >> >> to allow deterministic rendering to be defined at the point of
> >> >> authoring?
> >> >>
> >> >> Raising this issue for discussion at TPAC.
> >> >>
> >> >> Note that there are related issues (to be filed separately) around
> >> >> lineHeight=normal being related to the height of the text actually
> >> >> flowed
> >> >> onto a line (is it? or is it related to the descendent elements of
> the
> >> >> <p>?)
> >> >> and being set to a percentage of the font size - should it be 100%,
> >> >> 120%,
> >> >> 125% etc. for compatibility with CSS etc.
> >> >>
> >> >>
> >> >>
> >> >
> >
> >
>