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Re: WebVTT Horizontal writing direction

From: Thierry MICHEL <tmichel@w3.org>
Date: Thu, 05 Feb 2015 14:26:28 +0100
Message-ID: <54D36F84.9050802@w3.org>
To: Philip Jägenstedt <philipj@opera.com>
CC: public-tt@w3.org, Silvia Pfeiffer <silviapfeiffer1@gmail.com>
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 13:26:38 UTC

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