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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: Mon, 13 Jun 2016 18:00:38 +0900
To: <www-style@w3.org>
Cc: "'fantasai'" <fantasai.lists@inkedblade.net>, "'Shane Stephens'" <shans@google.com>, "'Brad Kemper'" <brad.kemper@gmail.com>
Message-ID: <005b01d1c552$0e252300$2a6f6900$@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 resolution?

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

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
[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 Monday, 13 June 2016 09:01:11 UTC

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