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

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
>> >> >> >>
>> >> >> >
>> >> >
>> >> >
>> >
>> >
>
>

Received on Sunday, 22 June 2014 00:57:47 UTC