On Thursday 2016-12-15 22:32 +0100, Simon Pieters wrote:
> On Thu, 15 Dec 2016 19:49:37 +0100, Greg Whitworth <gwhit@microsoft.com> wrote:
> > > In his original post, Alex said: "2) Only a hint during load. Once
> > > the asset (metadata) is loaded successfully, the actual aspect-ratio
> > > of the asset takes over. If the image fails to load, the image’s box
> > > retains the hint. This fails gracefully, in cases of sloppy
> > > authoring. It also allows conventional stretching via CSS, as Tommy
> > > Hodgins has requested. Basically, it should do its job and then get
> > > out of the way." (emphasis mine)
> >
> > This is a great point, that said there is nothing stopping us from
> > making it so that the CSS property can accomplish this and we should
> > ensure that the CSS property is able to do this. I would prefer to not
> > have an HTML attribute that behaves differently than the CSS property.
>
> It would not need to behave differently. If there are good reasons to have
> an HTML attribute (I recall someone mentioning lint checkers being able to
> check HTML attributes but not so much parse and apply CSS), we can define it
> as a "presentational hint" attribute that just maps to the CSS property. A
> lot of HTML presentational attributes do this.
I don't think this is necessarily the desired approach here.
I think it was a design mistake in the early days of HTML that the
height and width attributes on img overrode the intrinsic sizes of
the image, rather than just being hints for when the image was
loading. This has led to many unintentionally-scaled images, and
a decent number of images that use way more bandwidth than needed.
Had that mistake not been made, mapping the height and width
attributes on img into the 'height' and 'width' CSS properties
wouldn't have made sense. They would have instead mapped to
intrinsic dimensions (as defined in
https://drafts.csswg.org/css-images/#sizing-terms ).
Wanting a way to describe the intrinsic size of an external resource
so that relayout doesn't happen when the resource loads is a useful
goal. Making the mechanism for that have effects after the resource
has loaded, or interacting with the CSS model in any way other than
providing intrinsic dimensions (as defined above, including
intrinsic aspect ratio) prior to the resource being loaded,
complicates the mechanism and causes it to have undesired effects
for the simple (and important) use case of avoiding relayout.
This seems like it might become more important as developers do more
responsive things with images using some of the new mechanisms
available in CSS (e.g., object-fit/object-position, flexbox, grid,
and correct implementation of min/max-height/width).
-David
--
𝄞 L. David Baron http://dbaron.org/ 𝄂
𝄢 Mozilla https://www.mozilla.org/ 𝄂
Before I built a wall I'd ask to know
What I was walling in or walling out,
And to whom I was like to give offense.
- Robert Frost, Mending Wall (1914)