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Re: [css3-writing-modes] implementation costs for logical properties

From: David Hyatt <hyatt@apple.com>
Date: Tue, 26 Oct 2010 13:15:23 -0500
Cc: koba Mobile2 <koba@antenna.co.jp>, John Daggett <jdaggett@mozilla.com>, www-style@w3.org, howcome@opera.com
Message-id: <7774FAB5-1E5F-462E-BBFA-3C1AC6BDCF43@apple.com>
To: fantasai <fantasai.lists@inkedblade.net>
On Oct 25, 2010, at 8:12 PM, fantasai wrote:

> On 10/25/2010 05:52 PM, koba Mobile2 wrote:
>> John Daggett wrote:
>>> koba Mobile2 wrote:
>>>> Håkon Wium Lie wrote:
>>>>> Implementation cost is one metric, but no the only one. For one,
>>>>> there's also a memory cost. I presume you have implemented this so that
>>>>> the logical propertie cascade and inherit separately? on a per-element
>>>>> basis? And cannot be resolved until you know the computed value for
>>>>> 'writing-mode'? If so, the memory use will be significant: ~35
>>>>> property values for every element.
>>>> 
>>>> Your opinion is an excuse from an incompetent implementor.
>>> 
>>> No, it's the concern of an implementor who has a long history
>>> of developing browsers for devices that run with restricted memory.
>> 
>> All browsers are not asked to support all properties.
> 
> No, but desktop browsers and their equivalents are.
> 
> That said, the performance and memory considerations for logical
> properties are not as bad as they seem at first glance. Since
> you can compute the logical-physical equivalence at cascade time,
> you only need to store one set of data per element (physical or
> logical, depending on your layout architecture). So the extra
> memory load is almost nothing.
> 
> I could try to convince you that this is true, but I don't have
> to: Hyatt already implemented it this way and can confirm that
> this is the case.

Yeah the memory/perf cost is virtually 0.  The only extra memory consumed is in the back end declaration storage for rules, and then only if you have to specify a physical and logical for backwards compatibility.  Aside from the alternate stylesheet solution, all other proposed solutions share the same cost (two physical declarations vs. one physical/one logical declaration).   That is pretty inconsequential.  In terms of additional memory overhead per-element, there is none.

So yes, from an implementation perspective, the logical properties are trivial.

dave
(hyatt@apple.com)
Received on Tuesday, 26 October 2010 18:15:57 GMT

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