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]

On Fri, Aug 1, 2014 at 11:33 AM, Glenn Adams <glenn@skynav.com> wrote:

>
>
>
> 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.
>

Scratch that. I see that CSS [1] says otherwise.

*hidden*
The generated box is invisible (fully transparent, nothing is drawn), but
still affects layout. Furthermore, descendants of the element will be
visible if they have 'visibility: visible'.

[1] http://www.w3.org/TR/CSS2/visufx.html#propdef-visibility


>
>>
>>
>> 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.
>>> >> >>> -->
>>> >> >>>
>>> >> >>>
>>> >> >>>
>>> >> >>>
>>> >> >>
>>> >> >
>>> >
>>> >
>>>
>>
>>
>