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