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Re: WebVTT Horizontal writing direction

From: Philip Jägenstedt <philipj@opera.com>
Date: Thu, 5 Feb 2015 23:27:09 +0700
Message-ID: <CAMQvoCkLKCri-GFvaanQW6oqR4x5a60GTMPezv_t8JWcX9reag@mail.gmail.com>
To: Thierry MICHEL <tmichel@w3.org>
Cc: public-tt@w3.org, Silvia Pfeiffer <silviapfeiffer1@gmail.com>
Hi Thierry,

I'm not entirely sure what you mean by an equivalent to "vertical:rl"
for horizontal text. If you look at CSS you'll notice that there's no
way to have horizontal text grow upwards when breaking lines, so that
one would read it from bottom to top. That just isn't a thing, but
vertical text can be be arranged in both orders, much like horizontal
Chinese can also be written RTL occasionally.

As for the align setting, its influence is in the same direction as
the text grows character-by-character.

Please let me know if there's a particular rendering that is used "in
the wild" that you can't see how to achieve using WebVTT.

Philip

On Thu, Feb 5, 2015 at 8:26 PM, Thierry MICHEL <tmichel@w3.org> wrote:
> Philip,
>
> Thank you for your clarification.
>
> I had seen the possibilty to use escape &lrm; and &rlm;
>
> Without a equivalent to "vertical:rl" for horizontal text,
> is it an issue when using "align:" setting ?
>
> for vertical writting
>
>                 vertical:rl             vertical:lr
> "align:start"   top                     top
> "align:middle"  centred vertically      centred vertically
> "align:end"     bottom                  bottom
>
>
> for horizontal writting
>                 "RtL"                   "LtR"
> "align:start"   left                     right
> "align:middle"  centred horizontally     centred horizontally
> "align:end"     right                    left
>
>
> And same for "position:" cue setting
>
> "position:start" is left for horizontal writting LtR
> "position:start" is right for horizontal writting RtL
>
>
> I am not a I18N expert, but I am unclear who to solve this,
> for exemple see the TTML Example
> Rendition – Unicode Bidirectionality
> http://www.w3.org/TR/ttaf1-dfxp/#style-attribute-unicodeBidi
>
> Another solution would be the use of a class with direction CSS properties:
> .rtl {
>     direction: rtl;
>     unicode-bidi: bidi-override;
>       }
>
> But these CSS properties aren't allowed to apply to the '::cue'
> pseudo-element.
>
>
>
> Thierry
>
>
> On 05/02/2015 04:11, Philip Jägenstedt wrote:
>>
>> To get RTL you simply use a cue text which is RTL according to the
>> BiDi algorithm, and you can use &lrm; and &rlm; to where necessary in
>> mixed-directionality text.
>>
>> Note, however, that the equivalent to vertical:rl for horizontal text
>> would be control over which direction additional lines of texts grow,
>> up or down. We don't have explicit control over that, even though the
>> cue placement algorithm does move whole cues up or down.
>>
>> Philip
>>
>> On Wed, Feb 4, 2015 at 11:39 PM, Thierry MICHEL <tmichel@w3.org> wrote:
>>>
>>> Hi,
>>>
>>> WebVTT lastest draft [1]
>>> http://www.w3.org/TR/2014/WD-webvtt1-20141113/
>>> specifies the WebVTT vertical text cue setting
>>>
>>> A WebVTT vertical text cue setting configures the cue to use vertical
>>> text
>>> layout rather than horizontal text layout. Vertical text layout is
>>> sometimes
>>> used in Japanese, for example. The default is horizontal layout.
>>>
>>> vertical values:
>>> - vertical:rl   writing direction is right to left
>>> - vertical:lr   writing direction is left to right
>>>
>>>
>>> My issue is how can one set writing direction  "right to left" for
>>> horizontal text ? (example of arabic lang)
>>> I couldn't find explicit mention in the spec.
>>> like:
>>> - horizontal:rl         writing direction is right to left
>>> - horizontal:lr         writing direction is left to right
>>>
>>>
>>> Thierry
>>>
>>>   [1] http://www.w3.org/TR/2014/WD-webvtt1-20141113/
>>>
>>
>
Received on Thursday, 5 February 2015 16:27:37 UTC

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