Re: Line Height stacking strategy algorithm - approval needed

Hi Nigel,

Is the plan to backport these changes to TTML 1.0?


-- Pierre

On Fri, Jan 17, 2014 at 6:17 AM, Nigel Megitt <> wrote:
> 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].
> 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".
> 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.
> 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
> [2] Action-221
> [3] Issue-275
> [4] Issue-284
> [5] TTML2 Editor's draft, section on lineHeight
> [6] Action-260
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Received on Friday, 17 January 2014 20:47:50 UTC