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

> On Jun 14, 2016, at 2:07 AM, Brad Kemper <[email protected]> wrote:
>
>
> > then we also need something like 'offset-rotation-anchor',
> 
> Or maybe 'offset-path-anchor', since it should also determine where the initial position of the path
> aligns to the element.
> 

Is 'offset-path-anchor' different from 'offset-anchor'?
As I understand it, 'offset-path-anchor' sets the initial position of the path and 'offset-anchor' sets the origin of
the element which aligns on the path.

Do we need 'offset-path-anchor' as a separate property?

> >> 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.
> >
> > It isn't useful for angle values. The origin of the element is wherever other positioning properties
> (including 'top', etc. or 'offset-position') put it. If all those positioning properties are 'auto',
> then the origin is wherever the element would have been if it wasn't positioned. When you want the
> origin to be in the middle of the containing block, you would use 'offset-position: 50% 50%' (or
> 'offset-position: center', etc. that computes to the same).
> 
> And actually, for non-angle paths, the "initial position" refers to the position on the path, not the
> position of where that aligns with the element (see 'offset-path-anchor'), nor anything about its
> position in the containing block (top, right, bottom, left, and/or offset-position handle that). So
> I'm not sure what 'offset-origin' and "initial position" have to do with each other. "initial
> position" is only about where 'offset: distance:0' is on the path.

You're right. I was confused about that.
The "initial position" of the path isn't the same with the position specified with 'offset-origin'.

'offset-origin' ('offset-position') specifies the position of a path.
The initial position of the path is defined differently by the type of value given to 'offset-path'.

Then I would like to keep 'offset-origin' for defining the position of the path.
And the initial position of the path when the path is specified in <angle> would be the same with the position specified
by 'offset-origin'.

> Oh, and also, the initial value of 'offset-rotation' should be zero. It is weird to have to opt out of
> a transformation, just because you are moving something along an angle or other path.
> 
I agree with that.
But the initial value of 'motion-rotation'[1] in Motion Path is 'auto' and I referred to it.
I'm not sure which is better, '0deg' or 'auto'.

= Jihye

[1] https://www.w3.org/TR/motion-1/#propdef-motion-rotation