W3C home > Mailing lists > Public > www-style@w3.org > August 2009

Re: Shadows vs. layout

From: Tab Atkins Jr. <jackalmage@gmail.com>
Date: Mon, 3 Aug 2009 15:22:18 -0500
Message-ID: <dd0fbad0908031322t53efc5f8m93646f4cec7001c1@mail.gmail.com>
To: Andrew Fedoniouk <news@terrainformatica.com>
Cc: David Hyatt <hyatt@apple.com>, fantasai <fantasai.lists@inkedblade.net>, Brad Kemper <brad.kemper@gmail.com>, W3C style mailing list <www-style@w3.org>
On Mon, Aug 3, 2009 at 3:17 PM, Andrew
Fedoniouk<news@terrainformatica.com> wrote:
> David Hyatt wrote:
>>
>> On Aug 3, 2009, at 12:23 PM, fantasai wrote:
>>
>>> I completely agree. Added
>>>  "Shadows never affect layout, and do not trigger scrolling."
>>> to the spec, hopefully that's clear enough.
>>
>> I strongly disagree with this change and think it warrants further
>> discussion.
>>
>> Shadows in WebKit are visual overflow.  If you put a box-shadow on an
>> object near the bottom of a document, you'd expect to be able to scroll to
>> see that shadow.  It shouldn't simply be cut off.  I see no reason why
>> shadows would be special cased versus all of the other kinds of visual
>> overflow that can occur on a page.
>>
>> Shadows are clipped if they spill out of a box with overflow:hidden
>> specified. They are obviously overflow.  Why should overflow:scroll/auto
>> deliberately ignore this overflow just when scrolling? That makes no sense
>> to me, and is more memory-intensive to code.  You're saying the engine has
>> to track shadows as visual overflow for the purposes of accurate container
>> repainting, but then somehow track a completely second set of visual
>> overflow numbers that exclude shadows just to ensure that you don't include
>> shadow overflow when scrolling?  That's nuts.
>>
>> dave
>> (hyatt@apple.com)
>>
>>
>>
>
> Shadows and other types of outlines do not affect neither box
> dimensions nor dimensions of its container nor dimensions of
> scrollable content. By definition. (space/time and so on).
>
> E.g. window shadow is not causing scroll of desktop window not on Mac
> not on Windows and not on any other GUI system I know about.

To be fair, on the GUI systems you know about, the elements are
purposely placed so that the shadow doesn't try to 'spill out' of the
container.  So the question of overflow behavior doesn't come up.

In the web environment the issue is a bit different - it's easy to
make elements with shadows/outlines/border-images that have parts of
the visual effect spilling out.

~TJ
Received on Monday, 3 August 2009 20:23:17 GMT

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