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

Re: Shadows vs. layout

From: David Hyatt <hyatt@apple.com>
Date: Mon, 03 Aug 2009 15:21:41 -0500
Cc: fantasai <fantasai.lists@inkedblade.net>, Brad Kemper <brad.kemper@gmail.com>, W3C style mailing list <www-style@w3.org>
Message-id: <87CB357D-307F-4D1A-AA70-D9581F68619D@apple.com>
To: Andrew Fedoniouk <news@terrainformatica.com>
On Aug 3, 2009, at 3:17 PM, Andrew Fedoniouk 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).
>

Overflow obviously doesn't alter border box dimensions either.  It's  
merely about scrollable content.  Obviously I am not suggesting that  
the shadow influences the size of the object it's specified 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.
>

I think this is not a good example to bring up, since windows don't  
occur inside other content.  A better example would be iChat balloons  
or Aqua controls with shadows (which is most of them).  If these  
control shadows were cut off at the bottom of a page, the controls  
would look pretty weird.
Received on Monday, 3 August 2009 20:22:25 GMT

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