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Re: ISSUE-331 (forcedDisplay region background note): An advisory note on the use of backgrounds on regions in combination with forcedDisplay [TTML IMSC 1.0]

From: Glenn Adams <glenn@skynav.com>
Date: Fri, 1 Aug 2014 11:33:48 -0600
Message-ID: <CACQ=j+cJfEUburPiSnttmdQfOxkqd2-ePvGAJfPRC=YgPEjwjQ@mail.gmail.com>
To: Pierre-Anthony Lemieux <pal@sandflow.com>
Cc: Nigel Megitt <nigel.megitt@bbc.co.uk>, Timed Text Working Group <public-tt@w3.org>
On Fri, Aug 1, 2014 at 11:32 AM, Glenn Adams <glenn@skynav.com> wrote:

> Keep in mind that if some element E is not visible, then all of its
> children are not visible regardless of their visibility property.
>

To clarify, I mean if not visible due to computedValue(tts:visibility) ==
hidden. That is, the computed value of tts:visibility also prevents
rendering of descendants.


>
>
> On Fri, Aug 1, 2014 at 11:17 AM, Pierre-Anthony Lemieux <pal@sandflow.com>
> wrote:
>
>> Hi Glenn,
>>
>> Thanks. Sounds good.
>>
>> Per Nigel's earlier question: is specifying "inherited:yes" in the
>> attribute definition sufficient to enable inheritance similar to that
>> of tts:display?
>>
>> Thanks,
>>
>> -- Pierre
>>
>>
>> On Fri, Aug 1, 2014 at 6:51 PM, Glenn Adams <glenn@skynav.com> wrote:
>> >
>> > On Fri, Aug 1, 2014 at 10:21 AM, Pierre-Anthony Lemieux <
>> pal@sandflow.com>
>> > wrote:
>> >>
>> >> Hi Glenn,
>> >>
>> >> > Then it needs to be changed.
>> >>
>> >> What about the following:
>> >>
>> >> "If the value of displayForcedOnlyMode is "true", a content element
>> >> with a itts:forcedDisplay computed value of "false" shall be invisible
>> >> (fully transparent), but still affects layout, regardless of the value
>> >> of tts:visibility."
>> >
>> >
>> > s/shall be invisible (fully transparent)/shall not produce any visible
>> > rendering/
>> >
>> >>
>> >>
>> >> Thanks,
>> >>
>> >> -- Pierre
>> >>
>> >> On Fri, Aug 1, 2014 at 5:59 PM, Glenn Adams <glenn@skynav.com> wrote:
>> >> >
>> >> >
>> >> > On Fri, Aug 1, 2014 at 9:19 AM, Nigel Megitt <nigel.megitt@bbc.co.uk
>> >
>> >> > wrote:
>> >> >>
>> >> >> On 01/08/2014 16:01, "Glenn Adams" <glenn@skynav.com> wrote:
>> >> >>
>> >> >>
>> >> >> On Fri, Aug 1, 2014 at 7:51 AM, Timed Text Working Group Issue
>> Tracker
>> >> >> <sysbot+tracker@w3.org> wrote:
>> >> >>>
>> >> >>> ISSUE-331 (forcedDisplay region background note): An advisory note
>> on
>> >> >>> the
>> >> >>> use of backgrounds on regions in combination with forcedDisplay
>> [TTML
>> >> >>> IMSC
>> >> >>> 1.0]
>> >> >>>
>> >> >>> http://www.w3.org/AudioVideo/TT/tracker/issues/331
>> >> >>>
>> >> >>> Raised by: Nigel Megitt
>> >> >>> On product: TTML IMSC 1.0
>> >> >>>
>> >> >>> This issue is created to fulfil Action-314.
>> >> >>>
>> >> >>> Rationale:
>> >> >>>
>> >> >>> Since forcedDisplay affects the computed value of the
>> tts:visibility
>> >> >>> property
>> >> >>
>> >> >>
>> >> >> Actually it doesn't change the computed value of tts:visibility (or
>> >> >> shouldn't). It qualifies how the computed value is used, e.g., by
>> doing
>> >> >> something like:
>> >> >>
>> >> >> if (computedValue('tts:visibility') == 'visible') {
>> >> >>   if (!displayForcedOnlyMode ||
>> (computedValue('itts:forcedDisplay') !=
>> >> >> 'false')) {
>> >> >>     renderContent()
>> >> >>   }
>> >> >> }
>> >> >>
>> >> >>
>> >> >>
>> >> >> That would be one way to do it, but the current spec does seem to
>> state
>> >> >> that the tts:visibility computed value should change.
>> >> >
>> >> >
>> >> > Then it needs to be changed.
>> >> >
>> >> >>
>> >> >>
>> >> >> Aren't they completely equivalent though?
>> >> >
>> >> >
>> >> > No, since computed values are referenced elsewhere, e.g.,
>> inheritance.
>> >> >
>> >> >>
>> >> >> I don't see what the difference would be between your algorithm and:
>> >> >>
>> >> >> if (!displayForcedOnlyMode || (computedValue('itts:forcedDisplay')
>> >> >> !='false')) {
>> >> >>    setComputedValue('tts:visibility', 'visible')
>> >> >> }
>> >> >>
>> >> >> if (computedValue('tts:visibility')=='visible') {
>> >> >>    renderContent()
>> >> >> }
>> >> >
>> >> >
>> >> > The problem is that computed value is referenced elsewhere, and this
>> >> > logic
>> >> > shouldn't impact it.
>> >> >
>> >> >>
>> >> >>
>> >> >>> it has no effect on whether or not the hidden/visible content is
>> >> >>> temporally active. This means that if non-forced content is
>> assigned
>> >> >>> to a
>> >> >>> region with a background colour then the background will be shown
>> >> >>> whenever
>> >> >>> the content is active even if it is hidden. This is likely to be
>> >> >>> unexpected
>> >> >>> behaviour for some readers of the specification, who may imagine
>> that
>> >> >>> by
>> >> >>> using a setting of tts:showBackground of "whenActive" they can
>> prevent
>> >> >>> this
>> >> >>> effect.
>> >> >>>
>> >> >>> (incidentally they'd be correct in thinking this if forcedDisplay
>> were
>> >> >>> changed to do what its name suggests and affect tts:display, which
>> >> >>> arguably
>> >> >>> would be more useful functionality)
>> >> >>>
>> >> >>> Proposal:
>> >> >>>
>> >> >>> Include a non-normative note such as the following:
>> >> >>> <--
>> >> >>> NOTE
>> >> >>>
>> >> >>> If the forcedDisplay attribute is used for content in combination
>> with
>> >> >>> regions that have a non-transparent computed background color then
>> >> >>> authors
>> >> >>> should be aware that those regions' backgrounds will be drawn
>> whenever
>> >> >>> the
>> >> >>> selected content is active, even if the computed tts:visibility of
>> >> >>> that
>> >> >>> content is "none".
>> >> >>
>> >> >>
>> >> >> Note that the two legal values of tts:visibility are 'visible' and
>> >> >> 'hidden'. The values 'none' and 'false' and 'true' are not legal.
>> [IMSC
>> >> >> ED
>> >> >> currently refers to an illegal value 'true'.
>> >> >>
>> >> >>
>> >> >> Yes, sorry, my mistake – as Pierre also pointed out I meant
>> "hidden" in
>> >> >> place of "none".
>> >> >>
>> >> >>
>> >> >> BTW, I'd still like to see the name changed to itts:forced in order
>> to
>> >> >> avoid the display vs visibility confusion.
>> >> >>
>> >> >>
>> >> >>
>> >> >> I'd like to see it changed to itts:forcedVisibility to make it even
>> >> >> clearer, if we're going to change the name at all.
>> >> >>
>> >> >>
>> >> >>> One strategy for avoiding this scenario would be to assign content
>> >> >>> elements only to regions that have the same value of forcedDisplay.
>> >> >>> -->
>> >> >>>
>> >> >>>
>> >> >>>
>> >> >>>
>> >> >>
>> >> >
>> >
>> >
>>
>
>
Received on Friday, 1 August 2014 17:34:36 UTC

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