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[csswg-drafts] transform-origin: 0% not equivalent to 0px is confusing

From: Simon Fraser via GitHub <sysbot+gh@w3.org>
Date: Thu, 12 Jan 2017 17:10:39 +0000
To: public-css-archive@w3.org
Message-ID: <issues.opened-200425777-1484241038-sysbot+gh@w3.org>
smfr has just created a new issue for 

== transform-origin: 0% not equivalent to 0px is confusing ==

I think the behaviour of transform-origin, where lengths mean 
things depending on whether the element is an SVG element or not, 
great.  It leads to questions like:

- Why shouldn't 'transform-origin: 0px 0px' and 'transform-origin: 0% 
0%' mean the same thing?  Surely 0% of anything is 0, and so that 
be equivalent to 0px.

- How do we treat 'transform-origin: calc(0% + 0px) calc(0% + 0px)'?

What about having something in the property value that explicitly opts
in to having values be relative to the SVG viewport rather than the 
bounding box?  For example:

   transform-origin: viewport 50% 50%;  /* middle of the viewport */
   transform-origin: 50% 50%;           /* middle of the bbox */
   transform-origin: viewport 4px 4px;  /* relative to viewport origin
   transform-origin: 4px 4px;           /* relative to the bbox origin

And then the UA style sheet could set

   transform-origin: viewport 0 0;

on SVG elements.

Alternatively, since setting the transform origin to be anything 
viewport relative except for the origin isn't that useful -- and could
be handled by translations in the 'transform' property -- we could 
add a single new value which means the viewport origin for SVG 
and the bbox origin for other elements:

   transform-origin: auto;

This would then be the initial value, no need for a UA style sheet 
  Percentages and lengths would always be relative to the bbox.

Even if we don't do either of these, and leave the "percentages are 
interpreted differently" behaviour, we should define what happens with
calc()s that contain percentages.

Please view or discuss this issue at 
https://github.com/w3c/csswg-drafts/issues/895 using your GitHub 
Received on Thursday, 12 January 2017 17:10:45 UTC

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