Re: Line Height stacking strategy algorithm - approval needed

Hi Pierre,

The 125% wording we added to TTML1SE is informative only. I don't believe
that the proposed algorithm is contrary to that wording (and certainly not
to the intent) though it is more explicit about when the percentage rule
should apply and removes much of the ambiguity present previously.

That said, these changes are planned for TTML2 only. There's no proposal
to backport them to TTML1so far, but if you or another member would like
to make one then that option's available.

Kind regards,

Nigel


On 17/01/2014 20:46, "Pierre-Anthony Lemieux" <pal@sandflow.com> wrote:

>Hi Nigel,
>
>Is the plan to backport these changes to TTML 1.0?
>
>Thanks,
>
>-- Pierre
>
>On Fri, Jan 17, 2014 at 6:17 AM, Nigel Megitt <nigel.megitt@bbc.co.uk>
>wrote:
>> CONTEXT
>>
>> As discussed in yesterday's TTWG meeting, as part of the fulfilment of
>> actions 219 [1] and 221 [2] Glenn has edited the TTML2 editor's draft to
>> incorporate an algorithm for computing the value of line height, based
>>on
>> the code used by Mozilla, blink and webkit. This can additionally be
>> considered part of the solution to the line height problem which has
>>also
>> been raised in issues 275 [3] and 284 [4].
>>
>> WHAT HAS CHANGED
>>
>> The algorithm can be found at [5] in section 8.2.13 tts:lineHeight.
>>
>> I won't attempt to repeat Glenn's explanation of this algorithm, which I
>> scribed as best I could yesterday, except to note what may appear at
>>first
>> to be a substantive change to some, that the "125% of fontSize" rule
>>does
>> not always apply, but applies only when the font is not associated with
>> "font metrics that specify altitude A, descent D, and line gap G".
>>
>> FOLLOW-UP
>>
>> This algorithm is absent from CSS but, if this group's members are happy
>> with it, we should communicate it to the CSS WG, to maximise the time
>>for
>> them to raise any potential issues, or indeed choose to adopt it into
>>their
>> own output documentation, which we could then potentially reference.
>> Formally they will report any problems anyway at Last Call stage but I'd
>> rather seek early agreement when possible.
>>
>> ACTION REQUIRED NOW
>>
>> Please notify the group if there are any queries or objections to this
>> algorithm as it stands.
>>
>> We noted in yesterday's call that it was not possible to verify that IE
>> adopts the same algorithm, so it would be particularly useful if someone
>> from Microsoft could confirm that they are happy with it  Jerry, this
>> probably means you!
>>
>> Rather than making this an open-ended action I'll close this off and
>>state
>> that we have approval if there are no outstanding objections by the end
>>of
>> our next call on 30th Jan 2014.
>>
>>
>>
>> This email satisfies Action-260 [6].
>>
>>
>> References
>>
>> [1] Action-219 https://www.w3.org/AudioVideo/TT/tracker/actions/219
>> [2] Action-221 https://www.w3.org/AudioVideo/TT/tracker/actions/221
>> [3] Issue-275 https://www.w3.org/AudioVideo/TT/tracker/issues/275
>> [4] Issue-284 https://www.w3.org/AudioVideo/TT/tracker/issues/284
>> [5] TTML2 Editor's draft, section on lineHeight
>>
>>https://dvcs.w3.org/hg/ttml/raw-file/default/ttml2/spec/ttml2.html#style-
>>attribute-lineHeight
>> [6] Action-260 https://www.w3.org/AudioVideo/TT/tracker/actions/260
>>
>>
>>
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Received on Monday, 20 January 2014 08:38:42 UTC