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

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.
>>
>>
>>
>

Received on Friday, 11 October 2013 01:48:49 UTC