Re: [IMSC] Thoughts re: issue-312 -- itts:forcedDisplay

On Sat, Jun 21, 2014 at 6:43 PM, Pierre-Anthony Lemieux <pal@sandflow.com>
wrote:

> Hi Glenn,
>
> Thanks for these initial thoughts.
>
> > 3. evaluating this sub-tree in a postorder traversal, prune elements
> > if they are not a content element, if they have a condition attribute
> that evaluates to false,
>
> "Forced" does not remove the content element from layout and flow, but
> instead
> effectively sets the visibility to zero, like tts:visibility="hidden".
>

it should; why would one want it to occupy layout space if not selected?
that doesn't make any sense;

i don't see how to handle conditional content and conditional visibility; i
think the best you will get is the former


>
> Best,
>
> -- Pierre
>
> On Sat, Jun 21, 2014 at 5:38 PM, Glenn Adams <glenn@skynav.com> wrote:
> >
> >
> > On Sat, Jun 21, 2014 at 6:07 PM, Pierre-Anthony Lemieux <
> pal@sandflow.com>
> > wrote:
> >>
> >> > What do you mean by "application" in this context?
> >>
> >> The entity that is instructing the presentation processor to render
> >> the IMSC document.
> >>
> >> > I also don't know what parameter means in this context,
> >> > e.g., what does it mean vis-a-vis a TTML parameter, i.e.,
> >> > an attribute expressing a TTML parameter.
> >>
> >> It is not a TTML parameter, as in a ttp:*, but instead a state
> >> variable passed to the presentation processor instructing it to render
> >> or not non-forced content, like a function argument in a procedural
> >> language.
> >>
> >> > I am opposed to a one-off solution to a special case of the
> conditional
> >> >  content problem. And the forcedDisplay feature is exactly such a
> >> > special case.
> >>
> >> Can you think of a generic solution that would reduce to a single
> >> attribute controlling the rendering of forced content? If so, we could
> >> consider using it in IMSC.
> >
> >
> > I haven't given it much thought, but if we were to introduce as the
> general
> > mechanism a new element type:
> >
> > <tt:switch condition="expression">
> > ... content elements ...
> > </tt:switch>
> >
> > then we could also, or as an alternative, introduce an attribute
> @condition
> > on content element vocabulary, e.g.,
> >
> > <div condition="expression"/>
> >
> > where expression uses a simple expression language such as media queries
> > level 4 [1] or a derivative.
> >
> > [1] http://dev.w3.org/csswg/mediaqueries4/
> >
> > For example,
> >
> > <p condition="(forced)"/>
> >
> > <p condition="not (forced)"/>
> >
> > <p condition="(locale: en)"/>
> >
> > <p condition="not (locale: en)"/>
> >
> > <p condition="(forced) or not (locale: en)"/>
> >
> > ...
> >
> > Where the semantics of @condition is essentially changing step 3 of 9.3.3
> > [construct intermediate document] to read essentially as follows:
> >
> > 3. evaluating this sub-tree in a postorder traversal, prune elements if
> they
> > are not a content element, if they have a condition attribute that
> evaluates
> > to false, if they are temporally inactive, if they are empty, or if they
> > aren't associated with region R according to the [associate region]
> > procedure;
> >
> >>
> >>
> >> Thanks,
> >>
> >> -- Pierre
> >>
> >> On Fri, Jun 20, 2014 at 10:56 PM, Glenn Adams <glenn@skynav.com> wrote:
> >> >
> >> > On Fri, Jun 20, 2014 at 10:33 PM, Pierre-Anthony Lemieux
> >> > <pal@sandflow.com>
> >> > wrote:
> >> >>
> >> >> Hi Glenn,
> >> >>
> >> >> Thanks for the feedback.
> >> >>
> >> >> > no, [forcedDisplayModeParameter] should not be a parameter, in
> which
> >> >> > it would go into some
> >> >> > parameter namespace, but should be a metadata attribute,
> >> >> > ittm:forcedDisplay
> >> >>
> >> >> forcedDisplayModeParameter != itts:forcedDisplay.
> >> >> forcedDisplayModeParameter would be a parameter passed by the
> >> >> application to the processor, not a parameter within the document.
> >> >
> >> >
> >> > What do you mean by "application" in this context? I also don't know
> >> > what
> >> > parameter means in this context, e.g., what does it mean vis-a-vis a
> >> > TTML
> >> > parameter, i.e., an attribute expressing a TTML parameter.
> >> >
> >> >>
> >> >>
> >> >> > in other words, TTML will remain silent on any presentation
> semantics
> >> >> > of
> >> >> > such an attribute;
> >> >>
> >> >> How would interoperability be achieved?
> >> >
> >> >
> >> > By defining a standard mechanism for expressing conditional content
> >> > contingent on external processor state, e.g., selected language,
> whether
> >> > display of some content is forced or not, etc.
> >> >
> >> > I am opposed to a one-off solution to a special case of the
> conditional
> >> > content problem. And the forcedDisplay feature is exactly such a
> special
> >> > case.
> >> >
> >> >>
> >> >>
> >> >> Thanks,
> >> >>
> >> >> -- Pierre
> >> >>
> >> >> On Fri, Jun 20, 2014 at 8:58 PM, Glenn Adams <glenn@skynav.com>
> wrote:
> >> >> >
> >> >> > On Fri, Jun 20, 2014 at 7:05 PM, Pierre-Anthony Lemieux
> >> >> > <pal@sandflow.com>
> >> >> > wrote:
> >> >> >>
> >> >> >> Hi all,
> >> >> >>
> >> >> >> During our last call, I noted two concerns with the
> >> >> >> itts:forcedDisplay
> >> >> >> feature as currently drafted.
> >> >> >>
> >> >> >> (a) the semantics of the itts:forcedDisplay feature are not
> >> >> >> sufficiently specified
> >> >> >> (b) the representation of itts:forcedDisplay as an attribute is
> not
> >> >> >> desirable
> >> >> >
> >> >> >
> >> >> > that should read as a style attribute
> >> >> >
> >> >> >>
> >> >> >>
> >> >> >> To address (a), below is proposed prose:
> >> >> >>
> >> >> >> """
> >> >> >> The presentation processor SHALL accept an optional boolean
> >> >> >> parameter
> >> >> >> called forcedDisplayModeParameter, whose value may be set by the
> >> >> >> application. If not set, the value of forcedDisplayModeParameter
> >> >> >> shall
> >> >> >> be assumed to be equal to "false".
> >> >> >
> >> >> >
> >> >> > no, it should not be a parameter, in which it would go into some
> >> >> > parameter
> >> >> > namespace, but should be a metadata attribute, ittm:forcedDisplay
> >> >> >
> >> >> > i'm not sure why you wish to lengthen the name unnecessarily
> >> >> >
> >> >> >
> >> >> >>
> >> >> >>
> >> >> >> If the value of forcedDisplayModeParameter is "true", a content
> >> >> >> element with a itts:forcedDisplay computed value of "false" shall
> be
> >> >> >> assumed to have a tts:visibility computed value equal to "hidden",
> >> >> >> even if tts:visibility is otherwise set to "true".
> >> >> >> """
> >> >> >
> >> >> >
> >> >> > now, this is again placing style/presentation semantics on this
> >> >> > metadata
> >> >> > attribute, which is inapropriate
> >> >> >
> >> >> >>
> >> >> >>
> >> >> >> The idea is to essentially ignore the itts:forcedDisplay attribute
> >> >> >> unless otherwise specifically requested by the application.
> >> >> >
> >> >> >
> >> >> > i'm not sure what "requested by the application" means here
> >> >> >
> >> >> >>
> >> >> >> This also
> >> >> >> clarifies that itts:forcedDisplay has "no effect on content layout
> >> >> >> or
> >> >> >> composition, but merely determines whether composed content is
> >> >> >> visible
> >> >> >> or not."
> >> >> >
> >> >> >
> >> >> > if that is the purpose, then the tts:visibility property should be
> >> >> > used
> >> >> > and
> >> >> > therefore there is no need for a new forcedDisplay attribute
> >> >> >
> >> >> >>
> >> >> >> As next step, I plan to create examples.
> >> >> >>
> >> >> >> Re: (b), I am not comfortable rejecting a solution that users have
> >> >> >> devised and implemented based on actual use cases and in the
> absence
> >> >> >> of specific guidance and/or prohibition in TTML 1.0.
> >> >> >
> >> >> >
> >> >> > if those users expect that the TTWG would simply adopt a solution
> as
> >> >> > a
> >> >> > fait
> >> >> > accompli, then they are naive; an appropriate process would have
> been
> >> >> > to
> >> >> > bring use cases and requirements to the TTWG first, not bring a
> >> >> > solution
> >> >> > as
> >> >> > a given
> >> >> >
> >> >> > at this point, I think the best that can be hoped for IMSC is to
> >> >> > define
> >> >> > a
> >> >> > metadata attribute ittm:forcedDisplay which is described as a hint
> >> >> > that
> >> >> > the
> >> >> > associated content is intended to be selected as a candidate for
> >> >> > display
> >> >> > by
> >> >> > a higher level protocol (outside the scope of formally defined TTML
> >> >> > processing); in other words, TTML will remain silent on any
> >> >> > presentation
> >> >> > semantics of such an attribute;
> >> >> >
> >> >> > on the other hand, we may choose in TTML2 to define a conditional
> >> >> > content
> >> >> > mechanism similar to the SMIL or SVG switch element, that could
> >> >> > address
> >> >> > this
> >> >> > use case
> >> >> >
> >> >> >>
> >> >> >>
> >> >> >> Best,
> >> >> >>
> >> >> >> -- Pierre
> >> >> >>
> >> >> >
> >> >
> >> >
> >
> >
>