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Re: [css3-images] Reintroduce object-fit: none

From: L. David Baron <dbaron@dbaron.org>
Date: Wed, 26 Jan 2011 16:50:44 -0800
To: Leif Arne Storset <lstorset@opera.com>
Cc: www-style@w3.org, Philip J├Ągenstedt <philipj@opera.com>, "Simon Pieters (zcorpan)" <simonp@opera.com>
Message-ID: <20110127005044.GA19207@pickering.dbaron.org>
On Wednesday 2011-01-26 11:50 +0100, Leif Arne Storset wrote:
> I was asked recently whether and why 'object-fit: none' was removed
> from the spec. Digging in the archives, it seems the proposal to
> keep/revive it was forgotten amid other issues. So this is a request
> to re-introduce 'none' as a value for 'object-fit'. The definition
> would be "Render the content at its intrinsic dimensions,
> overflowing if necessary."
> 
> The use case is easy centering or positioning images without scaling
> them. Centering images vertically in a box can be a PITA today,
> especially if you don't know the dimensions. With image-fit:none, it
> is super-easy. Have a look at the attached demo (only supported in
> Opera 11, AFAIK).
> 
> (To avoid any confusion: There were objections to our proposal of
> another value, 'object-fit: auto', because the proposal was that
> behavior depend on content type. These issues do not affect the
> current proposal of 'object-fit: none', since no content-type
> negotation takes place for 'object-fit: none'.)

I think this is a bad idea.  (I think the 'object-fit: scale-down'
proposal later in the thread, however, is fine.)


The main things I don't like about it derive from the fact that it
causes replaced elements to overflow.  I now see that
object-fit:cover also does this, though I don't remember it doing
that the last time I read the proposal.  I'd really like to avoid
getting into a situation where overflow applies to replaced
elements; I'd prefer that they just never overflow their content
box.

(It's also quite inconsistent with what we ended up doing
about the interaction of border-radius and replaced elements, since
the border-radius is supposed to clip replaced elements.  What
happens with img { object-fit: cover; border-radius: 10px } ?)

I think making it easy to overflow is generally a bad thing:  layout
systems should make it easy for authors to do what they want in ways
that don't accidentally cause horrible layouts in a slightly
different situation (e.g., slightly different viewport size, font
size, etc.).  Having an object-fitting mode that overflows by
default fails this test (whereas 'scale-down' passes it).  This is
why I'd prefer that replaced elements not overflow their content
box.

Furthermore, I think we need to be solving vertical centering for
all elements, not just replaced elements.  We have some good
proposals (including flexbox) on the table, and I hope they're
implemented before 'object-fit' (which I think has substantially
less demand than good layout systems) is.  So I don't think we
should design 'object-fit' to solve use cases that should already be
solved by the time it's implemented.


It's also unclear to me how much sense both 'none' and 'scale-down'
make in a high-DPI world where CSS pixels mainly exist for
backwards-compatibility.

-David

-- 
L. David Baron                                 http://dbaron.org/
Mozilla Corporation                       http://www.mozilla.com/
Received on Thursday, 27 January 2011 00:51:29 GMT

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