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Re: [css3-background] Default shadow color

From: L. David Baron <dbaron@dbaron.org>
Date: Fri, 11 Mar 2011 12:15:21 -0600
To: Lea Verou <leaverou@gmail.com>
Cc: fantasai <fantasai.lists@inkedblade.net>, www-style@w3.org
Message-ID: <20110311181521.GA18515@pickering.dbaron.org>
On Friday 2011-03-11 07:19 +0200, Lea Verou wrote:
> Just wanted to point out that shadow interpolation from (or to)
> 'none' (the initial value) is also undefined.
> This results to each browser doing a different thing:
> http://jsfiddle.net/leaverou/3gw4K/
> - Webkit ignores inset until the transition is finished
> - Opera doesn't transition at all
> - Gecko seems to get it right (right as in looks smooth and not weird)

I think, depending on how you interpret the spec, it may or may not
be defined.  The transitions spec currently says:
  # shadow: interpolated via the color, x, y and blur components
  # (treating them as color and numbers where appropriate). In the
  # case where there are lists of shadows, the shorter list is
  # padded at the end with shadows whose color is transparent and
  # all lengths (x, y, blur) are 0. 

When I implemented this in Gecko, I assumed that 'none' was a list
of length 0, and the rule for handling uneven-length lists applied.
But we should probably state that explicitly.

The other interesting edge cases are:

 * animation between inset and not-inset.  We refuse to animate,
   which I think is probably the best choice.

 * animation between an item with a color and an item without (which
   ties in to the other recent discussion about what the default
   color for a shadow ought to be).  We also refuse to animate here.
   (And I think we probably handle animation of an item without a
   color against a missing item incorrectly, since we don't do the
   fade from transparent correctly.)  I'm not sure what the right
   thing here is, and I'd need to think further about how hard it
   would be to extract the correct computed value if we're using
   'currentColor' for the no-color case.  It's probably pretty hard
   if we're going to stick to our current no-color behavior for
   shadows, which is to use 'currentColor' *and* to inherit it as
   'currentColor', e.g., in
     <p style="text-shadow: 3px 3px">
       hello <span style="color:green">hello</span>
   I think that behavior is incorrect according to the "Computed
   Value:" line in css3-text (for text-shadow), but correct
   according to the "Computed Value:" line in css3-background (for
   box-shadow).  Those "Computed Value:" lines should probably be


L. David Baron                                 http://dbaron.org/
Mozilla Corporation                       http://www.mozilla.com/
Received on Friday, 11 March 2011 18:16:06 UTC

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