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Re: [css-round-display] Positioning elements with polar positioning and absolute positioning

From: Florian Rivoal <florian@rivoal.net>
Date: Tue, 22 Dec 2015 11:53:00 +0900
Cc: Jihye Hong <jh.hong@lge.com>, www-style list <www-style@w3.org>
Message-Id: <83D1FDAE-45E3-4373-9C18-4D652A90F404@rivoal.net>
To: Brad Kemper <brad.kemper@gmail.com>

> On Dec 19, 2015, at 10:46, Brad Kemper <brad.kemper@gmail.com> wrote:
> 
> Just do the ‘left’, ‘top’, ‘right’, and 'bottom' calculations first. Then:
> 
> —To find the origin of the polar movement: If ‘polar-distance’ is not ‘auto’, then add ‘left’ (or negative ‘right’ if ‘left’ is ‘auto’, or 0 if they are both ‘auto’) and ‘top’ (or negative ‘bottom’ if ’top’ is ‘auto’, or 0 if they are both ‘auto’) to the horizontal center coordinate and vertical center coordinate (respectively) of the containing block. Essentially, ‘left’ and ’top’ take the place of the two numbers of polar-origin. They are offsets from the center of the containing block.
> 
> or, an alternative:
> 
> —To find the origin of the polar movement: If ‘polar-distance’ is not ‘auto’, then add ‘left’ to the horizontal center coordinate and subtract ‘right’ from it. Add ’top’ to the vertical center coordinate and subtract ‘bottom’ from it (treat ‘auto’ as 0 for these origin-finding calculations). This is very similar to above, but ‘left’ and ‘right’ can combine, and so can ’top’ and ‘bottom’.
> 
> or, a different alternative:
> 
> —To find the origin of the polar movement: If ‘polar-distance’ is not ‘auto’, position with ‘left’, ‘top’, ‘right’, and ‘bottom’. If they are all ‘auto’, but ‘polar-distance’ is not, then center the element in its containing block. Then move the center of the positioned element by the specified polar distance and angle. This makes polar movement more like a transform, but automatically defaults the origin to the center if ‘left’, ‘top’, ‘right', and 'bottom' are all 'auto'.
> 
> or, a different alternative, my favorite, using new ‘center’ properties (‘center-x’ and ‘center-y’, and shorthand ‘center’):
> 
> —To find the origin of the polar movement: position with ‘left’, ‘top’, ‘right’, and ‘bottom’. If ‘left’ and ‘right’ are both ‘auto’, then position with ‘center-x’ property’s value (‘center-x:50%’ would put the center of the element at the horizontal center of the containing block). If ‘top’ and ‘bottom’ are both ‘auto’, then position with ‘center-y’ property’s value (‘center-y:50%’ would put the center of the element at the vertical center of the containing block). Then move the center of the positioned element by the specified polar distance and angle. All horizontal and vertical positioning, including centering, is done with explicit dedicated properties, and polar movement is done from wherever it ends up as a result (not from any built-in centering).
> 

[...]

> Plus ‘position:polar’ doesn’t allow the positioned items to be ‘position:fixed’.

I think this last point is the key. Being able to do fixed polar (or relative or sticky) polar instead of only absolute polar is interesting. The rest seems to matter less to me.

As long as you leave top/bottom/left/right auto, polar positioning does something sensible. As long as polar distance is auto, traditional positioning does something sensible. I am far from convinced that trying to use both at the same time gives anything useful. 

So from that point of view, any solution that keeps things working fine in one mode when the other is in auto seems acceptable to me.

Among the other alternatives, I'm not in favor of introducing a center property, as it too would have complex interactions with both polar and traditional positioning (not to forget that left/right/top/bottom influence position AND size) , and because centering is now a solved problem[1].

The simplest answer could be:
* If position is not relative/absolute/fixed/sticky, polar-* properties are ignored.
* otherwise, if polar-distance is auto, left/right/top/bottom are applied as usual, and other polar-* properties are ignored.
* otherwise, (polar-distance is not auto), left/right/top/bottom are ignored, and polar-* properties are applied.


[1] https://drafts.csswg.org/css-align/#self-alignment
Received on Tuesday, 22 December 2015 02:53:32 UTC

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