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Re: Positioned Layout proposal

From: Shelby Moore <shelby@coolpage.com>
Date: Wed, 20 Oct 2010 06:57:29 -0400
Message-ID: <0ddcef693217c0275eaa4aecdc46fe37.squirrel@sm.webmail.pair.com>
To: "Andrew Fedoniouk" <news@terrainformatica.com>
Cc: "Tab Atkins Jr." <jackalmage@gmail.com>, robert@ocallahan.org, "www-style list" <www-style@w3.org>
I am going to spend some more time thinking about the math and then trying
to provide a proof on what I suggested if it still holds true, and I will
come here at that time.  I can't do it now, because I am on a deadline to
get a project done.

Thanks for the information.


> ?--------------------------------------------------
> From: "Tab Atkins Jr." <jackalmage@gmail.com>
> Sent: Tuesday, October 19, 2010 4:43 PM
> To: <shelby@coolpage.com>
> Cc: <robert@ocallahan.org>; "www-style list" <www-style@w3.org>
> Subject: Re: Positioned Layout proposal
>
>>
>> I believe the important bit is that existing layout engines can handle
>> position:absolute elements because they always reference boxes earlier
>> in the tree.  It's impossible to create cycles when you have a
>> restriction like that.  (You can maybe create oscillating constraints,
>> but that's a different issue.)
>
>
> Just for the clarity: constraints are not oscillating.
>
> For linear sets of constraints you can get stable solution or none.
>
> Problem is that HTML/CSS exhibit non-linear behavior:
> Y=F(X) is a step function ( http://en.wikipedia.org/wiki/Step_function ).
>
> Set of non-linear equations (constraints) may have multiple solutions
> for some input values.
>
> That is actually what happens in CSS on overflow:auto containers when
> content fills the area almost in full (e.g. free space is less than height
> of
> text line or so).
>
>>
>> Unfortunately, that's slightly too restrictive for one of the
>> use-cases I have, so I'm experimenting with ways to safely allow
>> references to elements later in the document so that cycles are easy
>> to detect and break.
>>
>
> In this paper:
> http://www.cs.washington.edu/research/constraints/web/ccss-uwtr.pdf
> authors claim that they are able to deal with:
> <quote>
> The collection of constraints [in CSS that] may include cycles (i.e.
> simultaneous equalities and inequalities or redundant constraints) and
> conflicting preferences.
> </quote>
> but it seems that they reduced the task to linear equations only.
>
> ----------
>
> Something tells me that your idea is practically applicable only to
> popups (separate out-of-flow elements/windows).
> Popups do not affect layout of host elements - so you can bound any
> element on popup layer (e.g. desktop) to any element on CSS
> canvas layer.
>
> If you will reduce your task to such two layers where
> elements on popup layer do not affect positions of elements
> on canvas layer then you can get something relatively manageable.
>
> --
> Andrew Fedoniouk
>
> http://terrainformatica.com
>
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Received on Wednesday, 20 October 2010 10:57:57 GMT

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