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Regarding initial value of tts:lineHeight #87

plehegar opened this issue Nov 4, 2015 · 2 comments

Regarding initial value of tts:lineHeight #87

plehegar opened this issue Nov 4, 2015 · 2 comments


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@plehegar plehegar commented Nov 4, 2015

TTML1SE added a non-normative recommendation for lineHeight: 8.2.12: "Note: It is recommended that presentation processors use a computed line height that is 125% of the size of the largest applicable font size when the value normal is specified. The choice of 125% allows use of a font size of 0.8c in order to obtain a line height of 1c."

However, the WG had previously agreed to 120% which was codified in an editor's draft after closing ISSUE-275. The issue includes the rationale. The Note was a last minute change for the reason stated in the last sentence in the note.

Implementations had been developed to roughly 120% which was re-enforced by the editor's draft text.

This recommendation should be revisited and normative provisions added to TTML2.

Detailed background information can be found here:

This is also related to ISSUE-283 and ISSUE-302.

(raised by Mike Dolan on 2013-10-11)
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@skynavga skynavga changed the title value of lineHeight Regarding initial value of tts:lineHeight. Sep 10, 2016
@skynavga skynavga changed the title Regarding initial value of tts:lineHeight. Regarding initial value of tts:lineHeight Sep 13, 2016

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@nigelmegitt nigelmegitt commented Dec 16, 2016

Note that ISSUE-283 was moved to #86 and ISSUE-302 to #101 here.

Also, for CSS in general the equivalent to tts:lineHeight="normal" would be line-height: normal; for which implementations offer varying default equivalent percentages, which in any case are only fallbacks in case the data in the font cannot provide a calculated value.

I'm not clear what normative provisions yoyu wanted to add to TTML2 @mikedo ? Some work has been done on tts:lineHeight to define the algorithm when the value is "normal" and this remains work in progress I think.


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@skynavga skynavga commented May 4, 2017

Marking as works for me and closing. If @mikedo still thinks this needs revisiting, then please reopen and add discussion needed label.

@skynavga skynavga closed this May 4, 2017
@skynavga skynavga removed their assignment May 22, 2017
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