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Re: Clarification needed regarding tts:overflow

From: Andreas Tai <tai@irt.de>
Date: Sun, 03 Nov 2013 19:27:10 +0100
Message-ID: <5276957E.4020901@irt.de>
To: Glenn Adams <glenn@skynav.com>
CC: public-tt <public-tt@w3.org>
Apalogies if I did not made my intention clear enough. It was to prove 
that my interpretation is not correct and that the use of the feature is 
as defined in XSL:FO and CSS.

My original interpretation of tts:overflow was always that it has the 
same semantics as in CSS. But in a conversation the part highlighted 
below was mentioned and I needed some clarification.

In general I see it as a huge benefit that the layout and formatting of 
TTML is nearly fully compatible with CSS. This allows a smooth 
integration in web technologies like HTML 5.

Thanks and best regards,

Andreas

Am 03.11.2013 07:10, schrieb Glenn Adams:
> Basically, TTML is doing precisely what XSL-FO and CSS both do here, 
> as defined by the preliminary material in [1]. If you find yourself 
> interpreting TTML style properties in a way that is distinct from CSS 
> semantics, then you should question your interpretation first. We 
> never intentionally diverge except in noted extensions, particularly 
> the use of 'c' metric and the potential use of an anamorphic font size.
>
> [1] http://www.w3.org/TR/CSS2/visufx.html#overflow-clipping
>
> On Sat, Nov 2, 2013 at 12:00 PM, Andreas Tai <tai@irt.de 
> <mailto:tai@irt.de>> wrote:
>
>     Thanks Glenn for the clarification!
>
>
>>
>>
>>         >From the TTML Spec:
>>
>>         "If the value of this attribute is visible [...] region
>>         composition and layout must be performed as if the region's
>>         width and height were unconstrained" [1]
>>
>>         >From my reading content that overflows the region extents
>>         the "box" of the region.
>>
>>
>>     No. It merely goes outside of that box (and is not clipped by it).
>>
>>         That is different what is shown in the first example of
>>         tts:overflow where the background color is only applied to
>>         the contrained region extent. Only the text content is
>>         rendered outside of the regions box.
>>
>>
>>     The size of the box should not be changed for the purpose of
>>     drawing its background.
>
>     OK. Seems that I misunderstood it. But from the conversation I had
>     with others I am not the only one. From my view the text marked in
>     red (and '*') leads to this misreading. From my view it would be
>     better to omit it (but possibly it is to late for a change).
>
>     "If the value of this attribute is|visible|, then content should
>     not be clipped outside of the affected region*, and region
>     composition and layout must be performed as if the region's width
>     and height were unconstrained, but with a well-defined origin*. "
>
>
>     - Andreas
>
>
>     Am 01.11.2013 18:56, schrieb Glenn Adams:
>>
>>     On Fri, Nov 1, 2013 at 10:30 AM, Andreas Tai <tai@irt.de
>>     <mailto:tai@irt.de>> wrote:
>>
>>         I need some clarification regarding the tts:overflow [1]
>>         attribute in TTML 1.0 (2nd edition).
>>
>>         1) Is this attribute only an indicator how presentation
>>         processors should handle content that overflows a region?
>>
>>         In the description of the desired presentation behaviour for
>>         "visible" and "hidden" the key word "should" and not "must"
>>         is used.
>>         (This seems to reflect the usage of overflow in XSL 1.1 and CSS)
>>
>>
>>     Yes. I suspect we used "should not be clipped" because other
>>     semantics outside the scope of interpreting this property may
>>     cause clipping.
>>
>>
>>         2) Does tts:overflow "hidden" create a "dynamic sized region"
>>         where width and height adopts to the size of the content?
>>
>>
>>     No. It simply behaves as if the region into which this content is
>>     selected is unconstrained in width (or height) in the inline
>>     progression dimension.
>>
>>
>>         >From the TTML Spec:
>>
>>         "If the value of this attribute is visible [...] region
>>         composition and layout must be performed as if the region's
>>         width and height were unconstrained" [1]
>>
>>         >From my reading content that overflows the region extents
>>         the "box" of the region.
>>
>>
>>     No. It merely goes outside of that box (and is not clipped by it).
>>
>>         That is different what is shown in the first example of
>>         tts:overflow where the background color is only applied to
>>         the contrained region extent. Only the text content is
>>         rendered outside of the regions box.
>>
>>
>>     The size of the box should not be changed for the purpose of
>>     drawing its background.
>>
>>
>>         Furthermore I believe that if the constrain is meant in that
>>         way it is not compatible with CSS.
>>
>>
>>     I'm not sure what you mean here. Could you be more precise, and
>>     provide an example (in both TTML and HTML/CSS)?
>>
>>
>>         - Andreas
>>
>>         [1] http://www.w3.org/TR/ttaf1-dfxp/#style-attribute-overflow
>>
>>
>>
>
>
>     -- 
>     ------------------------------------------------
>     Andreas Tai
>     Production Systems Television IRT - Institut fuer Rundfunktechnik GmbH
>     R&D Institute of ARD, ZDF, DRadio, ORF and SRG/SSR
>     Floriansmuehlstrasse 60, D-80939 Munich, Germany
>
>     Phone:+49 89 32399-389  <tel:%2B49%2089%2032399-389>  | Fax:+49 89 32399-200  <tel:%2B49%2089%2032399-200>
>     http:www.irt.de  <http://www.irt.de>  | Email:tai@irt.de  <mailto:tai@irt.de>
>     ------------------------------------------------
>
>     registration court&   managing director:
>     Munich Commercial, RegNo. B 5191
>     Dr. Klaus Illgner-Fehns
>     ------------------------------------------------
>
>


-- 
------------------------------------------------
Andreas Tai
Production Systems Television IRT - Institut fuer Rundfunktechnik GmbH
R&D Institute of ARD, ZDF, DRadio, ORF and SRG/SSR
Floriansmuehlstrasse 60, D-80939 Munich, Germany

Phone: +49 89 32399-389 | Fax: +49 89 32399-200
http: www.irt.de | Email: tai@irt.de
------------------------------------------------

registration court&   managing director:
Munich Commercial, RegNo. B 5191
Dr. Klaus Illgner-Fehns
------------------------------------------------
Received on Sunday, 3 November 2013 18:28:04 UTC

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