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From: Chris Beall on 9 Dec 2009 19:38
Ref: http://www.w3.org/TR/CSS21/colors.html#propdef-background-image

The reference includes several statements about what should be done by a
UA when a background image has an unknown height, width or aspect ratio,
including the case where none of these values is known.

How can an image NOT have an intrinsic height or width? i.e. under what
conditions do these rules come into play?

Chris Beall
From: dorayme on 9 Dec 2009 22:48
In article <hfpfuu$69v$1(a)news.eternal-september.org>,
Chris Beall <Chris_Beall(a)prodigy.net> wrote:

> Ref: http://www.w3.org/TR/CSS21/colors.html#propdef-background-image
>
> The reference includes several statements about what should be done by a
> UA when a background image has an unknown height, width or aspect ratio,
> including the case where none of these values is known.
>
> How can an image NOT have an intrinsic height or width? i.e. under what
> conditions do these rules come into play?
>

Browser generated ones?

<http://dev.w3.org/csswg/css3-images/#gradients->

CSS3.

Or perhaps vector ones that are attempted by an author? Perhaps some
browsers (future ones) will succeed in displaying such all by themselves
and need some general guidance about the matter, your URL perhaps
providing some guidelnes.

--
dorayme
From: Chris Beall on 10 Dec 2009 12:23
dorayme wrote:
> In article <hfpfuu$69v$1(a)news.eternal-september.org>,
> Chris Beall <Chris_Beall(a)prodigy.net> wrote:
>
>> Ref: http://www.w3.org/TR/CSS21/colors.html#propdef-background-image
>>
>> The reference includes several statements about what should be done by a
>> UA when a background image has an unknown height, width or aspect ratio,
>> including the case where none of these values is known.
>>
>> How can an image NOT have an intrinsic height or width? i.e. under what
>> conditions do these rules come into play?
>>
>
> Browser generated ones?
>
> <http://dev.w3.org/csswg/css3-images/#gradients->
>
> CSS3.
>
> Or perhaps vector ones that are attempted by an author? Perhaps some
> browsers (future ones) will succeed in displaying such all by themselves
> and need some general guidance about the matter, your URL perhaps
> providing some guidelnes.
>

In CSS1 (Ref: http://www.w3.org/TR/2008/REC-CSS1-20080411/#background-image)
there is no mention of intrinsic size with regard to background-image.

The rules for dealing with unknown intrinsic size were added for CSS2,
yet I can find no explanation of how such a situation might occur in a
CSS2 environment.

In CSS3 (Ref:
http://www.w3.org/TR/2009/WD-css3-background-20091015/#the-background-size)
the rules have been simplified and appear within the description of the
background-size property. Again, there is no information about how such
a situation would occur. (This is a Working Draft document, not yet
finalized).
For gradients, the applicable rule seems to be "the box refers to the
rectangle that would be filled by an SVG image without intrinsic
dimensions used in the same context." It then refers back to the CSS2.1
spec for clarification! That's a rather special case and, IMO, does not
fully explain when the rule under background-size would apply.

So my questions are:
- In the context of CSS2.x, how would the 'unknown intrinsic size'
rules come into play? Given that someone obviously spent some time
concocting these rules, it would seem odd to me if the answer were,
"There is no way this can occur."
- Is there a way to force entry into these rules, i.e. to cause the
intrinsic size of an image to become 'unknown'?

The first question is academic, the second, unless the answer is 'No',
might have practical value.

Chris Beall



From: dorayme on 11 Dec 2009 04:21
In article <hfrari$phd$1(a)news.eternal-september.org>,
Chris Beall <Chris_Beall(a)prodigy.net> wrote:

> dorayme wrote:
> > In article <hfpfuu$69v$1(a)news.eternal-september.org>,
> > Chris Beall <Chris_Beall(a)prodigy.net> wrote:
> >
> >> Ref: http://www.w3.org/TR/CSS21/colors.html#propdef-background-image
> >>
> >> The reference includes several statements about what should be done by a
> >> UA when a background image has an unknown height, width or aspect ratio,
> >> including the case where none of these values is known.
> >>
> >> How can an image NOT have an intrinsic height or width? i.e. under what
> >> conditions do these rules come into play?
> >>
> >
> > Browser generated ones?
> >
> > <http://dev.w3.org/csswg/css3-images/#gradients->
> >
> > CSS3.
> >
> > Or perhaps vector ones that are attempted by an author? Perhaps some
> > browsers (future ones) will succeed in displaying such all by themselves
> > and need some general guidance about the matter, your URL perhaps
> > providing some guidelnes.
> >
>
> In CSS1 (Ref: http://www.w3.org/TR/2008/REC-CSS1-20080411/#background-image)
> there is no mention of intrinsic size with regard to background-image.
>
> The rules for dealing with unknown intrinsic size were added for CSS2,
> yet I can find no explanation of how such a situation might occur in a
> CSS2 environment.
>
> In CSS3 (Ref:
> http://www.w3.org/TR/2009/WD-css3-background-20091015/#the-background-size)
> the rules have been simplified and appear within the description of the
> background-size property. Again, there is no information about how such
> a situation would occur. (This is a Working Draft document, not yet
> finalized).
> For gradients, the applicable rule seems to be "the box refers to the
> rectangle that would be filled by an SVG image without intrinsic
> dimensions used in the same context." It then refers back to the CSS2.1
> spec for clarification! That's a rather special case and, IMO, does not
> fully explain when the rule under background-size would apply.
>

It is possible, surely, that some provision is being made for where
there is no information about intrinsic size. The rules apply when this
happens. It is like saying to someone, "cross enemy lines and if there
are no tanks there, do this; if there are tanks, do that; if something
unexpected happens that makes it hard to decide what to do, contact H/Q
on this frequency..." without giving examples. I agree that in this case
one can imagine various things like the enemy have 100,000 naked
martians surrounding the target. Best I can do with the image equivalent
is mention vector graphics. My only hypothesis is that the possibility
is being *left open*.

> So my questions are:
> - In the context of CSS2.x, how would the 'unknown intrinsic size'
> rules come into play? Given that someone obviously spent some time
> concocting these rules, it would seem odd to me if the answer were,
> "There is no way this can occur."
> - Is there a way to force entry into these rules, i.e. to cause the
> intrinsic size of an image to become 'unknown'?
>
> The first question is academic, the second, unless the answer is 'No',
> might have practical value.
>

--
dorayme
From: Manuel Collado on 11 Dec 2009 04:28
Chris Beall escribi�:
> Ref: http://www.w3.org/TR/CSS21/colors.html#propdef-background-image
>
> The reference includes several statements about what should be done by a
> UA when a background image has an unknown height, width or aspect ratio,
> including the case where none of these values is known.
>
> How can an image NOT have an intrinsic height or width? i.e. under what
> conditions do these rules come into play?

It is possible to have external graphics formats that only use relative
sizes for its components, thus having no absolute "natural" or
"intrinsic" size.

Just an idea.
--
Manuel Collado - http://lml.ls.fi.upm.es/~mcollado
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