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

On Sat, Jun 21, 2014 at 7:32 PM, Pierre-Anthony Lemieux <pal@sandflow.com>
wrote:

> I have confirmed that the intent is tts:visibility="hidden".
>
> Why would this be a problem?
>

I suppose we could also make @condition apply to the set element in order
to conditionally apply a style based on a condition expression, e.g.,

<p tts:visibility="hidden">
  <set condition="(forced)" tts:visibility="visible"/>
  Forced Content
</p>


>
> -- Pierre
>
>
> On Sat, Jun 21, 2014 at 5:56 PM, Pierre-Anthony Lemieux
> <pal@sandflow.com> wrote:
> > Hi Glenn,
> >
> >> why would one want it to occupy layout space if not selected?
> >> that doesn't make any sense;
> >
> > The forced content would have been positioned with the non-forced
> > content present. Simply removing the non-forced content from flow
> > would potentially change the rendered position of the forced content.
> >
> > I will confirm this.
> >
> > Best,
> >
> > -- Pierre
> >
> > On Sat, Jun 21, 2014 at 5:50 PM, Glenn Adams <glenn@skynav.com> wrote:
> >>
> >> 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
> >>> >> >> >>
> >>> >> >> >
> >>> >> >
> >>> >> >
> >>> >
> >>> >
> >>
> >>
>