Re: [ttml2] Does tts:backgroundImage affect size of content area?

Could you please explain? What is invalid?

On Mon, Apr 18, 2016 at 8:46 AM, Michael Dolan <mdolan@newtbt.com> wrote:

> This condition is an invalid document and thus decoder behavior is
> undefined.
>
>         Mike
>
> -----Original Message-----
> From: Glenn Adams via GitHub [mailto:sysbot+gh@w3.org]
> Sent: Saturday, April 16, 2016 1:47 PM
> To: public-tt@w3.org
> Subject: [ttml2] Does tts:backgroundImage affect size of content area?
>
> skynavga has just created a new issue for
> https://github.com/w3c/ttml2:
>
> == Does tts:backgroundImage affect size of content area? == According to
> SMTPE ST2052-1:2013 §5.5.6:
>
> > The min-height and min-width of the area associated with the image
> shall be set to the intrinsic height and width of the image source.
>
> and
>
> > The presented image shall not be scaled and the XSL background-color
>  trait shall be visible for any background areas of the ``<div>``
> outside the image, therefore, authors should ensure that the div will
> be sized to match the given pre-rendering.
>
> The effects of these two requirements are that if an image is larger
> than the nominal minimum content size of the generated area, then that
>  minimal content size is to be increased to encompass the intrinsic
> image size as required. While if the nominal minimum content size is
> already larger than the intrinsic image size, the background color of
> the generated area (if not transparent) will be visible outsize the
> image, i.e., the image is not scaled in either dimension to fill the
> nominal minimum content size in such a case.
>
> IMSC1, which makes use of the ``smpte:backgroundImage`` extension,
> does not specify any details about sizing, other than to say that the
> intrinsic image size must correspond to the size of the region into
> which its associated generated area(s) are flowed. As such, one may
> presume that IMSC1 intends the above language from ST2052 to apply
> (Pierre?).
>
> The problem here is that this behavior is at variance with both XSL-FO
>  and CSS, where the minimum content size of generated areas associated
>  with a background image **is not** increased to the intrinsic image
> size. In other words, in XSL-FO or CSS, if there is no content in the
> element, then no area is generated, or if one is generated, it has
> zero for one or both content area dimensions. On the other hand, if
> there is content in the element, but its nominal formatted size is
> smaller than the intrinsic size of the background image, then some of
> the image will be clipped. I am attaching a test file that
> demonstrates the CSS behavior below.
>
> Now, the problem here in TTML2 is how to handle this discrepancy
> w.r.t. XSL-FO and CSS introduced by SMPTE-TT and apparently adopted by
>  IMSC1. One way to handle it would be to require that ``tts:ipd`` and
> ``tts:bpd`` be used with TTML2 if one wants such behavior with a
> background image (in a like manner to how one is forced to specify
> width and height properties in XSL-FO or CSS). Or we could add a
> ``tts:{ipdMinimum,bpdMinimum}`` pair in TTML2 to specify instead. Or
> we could generalize the values of ``tts:{ipd,bpd}`` to allow
> specifying a (minimum, optimum, maximum) tuple. Or we could allow the
> minimum values of these properties to be specified with a keyword, say
>  ``backgroundImageSize``.
>
> In any case, we have an issue here, so I have added an editorial note
> to the section on
> (tts:backgroundImage)[
> https://rawgit.com/w3c/ttml2/master/spec/ttml2.html#style-attribute-backgroundImage
> ]
>  in the TTML2 ED.
>
> Following is the CSS example file:
>
> [test.html.zip](https://github.com/w3c/ttml2/files/222397/test.html.zip)
>
>
>
> Please view or discuss this issue at
> https://github.com/w3c/ttml2/issues/157 using your GitHub account
>
>
>