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

From: Brad Kemper <brad.kemper@gmail.com>
Date: Mon, 13 Jun 2016 10:07:25 -0700
Message-Id: <EA8D5E26-C5C1-45FE-B8A3-810689D63D6D@gmail.com>
To: www-style list <www-style@w3.org>, jh.hong@lge.com

Brad Kemper
> On Jun 13, 2016, at 9:11 AM, Brad Kemper <brad.kemper@gmail.com> wrote:
> If we have a 'offset-rotation' ins treat of using transforms,

s/ins treat of/instead of

> 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. 

> the equivalent of 'motion-origin' that is mentioned in the motion path FPWG.

Or we could just use transform-origin, and ignore the third value of it. 

> We can't really use offset-anchor for both without getting unwanted side effects.


> You have 'offset-anchor' described as "Defines an origin of the element in the path." But as discussed, it should work with offset-position to set the alignment point of the element ('auto' for 'offset-position:<percentage>' would copy percentages from offset-position) to set the alignment point in the element to align to the offset-position point in the containing block). 
>> 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. 

> Yes. All other specs that use angles, including linear-gradient, have 0deg = north.  
> You should clarify the airplane example by showing what the unrotated plane looks like (with its nose at the top).

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. 

This would change how "initial direction" is described. It should be called "initial rotation", and it should only affect things with 'offset-rotation:auto'. 
Received on Monday, 13 June 2016 17:07:55 UTC

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