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[css-round-display][motion-path] Integrate polar positioning to the motion path spec

From: Jihye Hong <jh.hong@lge.com>
Date: Tue, 14 Jun 2016 09:38:55 +0900
To: <public-fx@w3.org>
Message-ID: <001e01d1c5d5$22045430$660cfc90$@lge.com>
At the SF f2f, there was an resolution [1][2] to integrate polar positioning to Motion Path [3].
Some properties from CSS Round Display are merged into Motion Path: 
   * polar-angle + motion-path => offset-path
   * polar-distance + motion-offset => offset-distance
   * polar-origin => offset-origin
   * polar-anchor => offset-anchor
My extra proposal(Not included in the resolution): 
   * 2d rotation transform extension + motion-rotation => offset-rotation

I just wrote the draft [4] about that to discharge the resolution.
Could you review the draft and check if there are any missing parts or incorrect things about the

Also, while writing it I ran into some issues that we need to discuss.

1. Proper term of the 'path'
'motion-path' is changed to 'offset-path', so it is not just about motion. Defining the path is
describing the possible position for the element.
Is it okay to use the term 'path' instead of 'motion path'?

2. Need for 'offset-origin'

'offset-origin' can set the initial position of the path. 
But in the specification of 'offset-path', the value types except for <angle> already define the
initial position for each case.
Therefore, 'offset-origin' is useful only when 'offset-path' is specified with <angle> value type.

There could be some solution about this:
  i. Keep 'offset-origin' and make it works only when <angle> type value is given to 'offset-path'.
  ii. Define the initial position of the path as the center of the containing block when the path is
defined by <angle> value and drop 'offset-origin'.

Which would be better?

3. The direction where 0deg points
When 'offset-path' is given to 0deg, the path points the direction of the positive y-axis. 
But in the specification of 'motion-rotation', 0deg means the right side in the direction of the
positive x-axis. I know that this is the common way in mathematical theory but in the CSS Value Spec
[5], 0deg is defined as the upside direction.
So I think it would be better to specify 0deg as the direction of the positive y-axis.


[1] https://lists.w3.org/Archives/Public/www-style/2016May/0233.html
[2] https://lists.w3.org/Archives/Public/www-archive/2016May/att-0000/whiteboard.jpg 
[3] https://drafts.fxtf.org/motion-1/ 
[4] https://drafts.csswg.org/css-round-display/#positioning-content
[5] https://drafts.csswg.org/css-values-3/#angle-value 
Received on Tuesday, 14 June 2016 00:39:31 UTC

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