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[css3-images] Images with an intrinsic aspect ratio and exactly one of an intrinsic height or width

From: L. David Baron <dbaron@dbaron.org>
Date: Wed, 14 Mar 2012 16:04:18 -0500
To: www-style@w3.org
Message-ID: <20120314210418.GA17204@pickering.dbaron.org>
The prose in http://dev.w3.org/csswg/css3-images/#default-sizing
(5.3, Default Concrete Object Size Resolution) seems to assume that
if an image has an intrinsic aspect ratio, it either has neither or
both of an intrinsic width and height.

In particular, if you work through the rules given an image with an
intrinsic aspect ratio and exactly one of an intrinsic width or
height, bad results occur in this case:

  # If the specified size has neither a definite width nor height,
  # and has no additional contraints, the dimensions of the concrete
  # object size are calculated as follows: 
  #
  # 1. If the object has only an intrinsic aspect ratio, the
  #    concrete object size must have that aspect ratio, and
  #    additionally be as large as possible without either its height
  #    or width exceeding the height or width of the default object
  #    size. Otherwise, the width and height of the concrete object
  #    size is the same as the object's intrinsic width and intrinsic
  #    height, if they exist. 
because of the use of the phrase "has only an intrinsic aspect
ratio" which I assume means "has an intrinsic aspect ratio but has
neither an intrinsic width nor intrinsic height" (though it's really
not at all clear).

However,
http://www.w3.org/TR/2011/REC-SVG11-20110816/coords.html#IntrinsicSizing
certainly defines cases where there's an intrinsic aspect ratio
(from a viewBox) and only one of an intrinsic width or height.

I think the better fix is to make the above text better handle the
case where the object has only one of an intrinsic width or height
and does have an intrinsic aspect ratio.

(Alternatively, we could try and make that situation not happen by
fixing SVG's definitions.)

-David

-- 
𝄞   L. David Baron                         http://dbaron.org/   𝄂
𝄢   Mozilla                           http://www.mozilla.org/   𝄂
Received on Wednesday, 14 March 2012 21:04:47 GMT

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