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Re: 'clip' property and the behavior on 'auto'

From: Dirk Schulze <dschulze@adobe.com>
Date: Thu, 11 Oct 2012 08:30:12 -0700
To: Robert Longson <longsonr@gmail.com>
CC: "www-svg@w3.org" <www-svg@w3.org>
Message-ID: <E7BB4DD0-C592-405E-BFE0-BF1F2AA87469@adobe.com>

On Oct 11, 2012, at 8:21 AM, Dirk Schulze <dschulze@adobe.com> wrote:

> 
> On Oct 11, 2012, at 7:15 AM, Robert Longson <longsonr@gmail.com> wrote:
> 
>> 
>>> In CSS 2.1 it says
>>> 
>>> 'auto' The element does not clip.
>> SVG is precisely on how to use 'auto'. I don't think that "Firefox implements CSS 2.1" means that SVG can't override the definition. That is why I ask if we can remove this clarification for SVG elements.
>> 
>> What I really meant was that we parse rect arguments per CSS 2.1 rather than per CSS 2.0 which is not compliant with SVG 1.1 but, I hope will be compliant with SVG 2
> Yes, it is in the current draft of SVG2 and in CSS Masking (which replaces the section in SVG) as well.
> 
>> 
>> 
>>> 
>>> If you want clipping you need an overflow value other than visible (This value indicates that content is not clipped per CSS 2.1) and you want the svg width/height to be larger than the clip region to see clipping occur.
>> 'overflow' with 'visible' says:
>> 
>> "This value indicates that content is not clipped, i.e., it may be rendered outside the block box."
>> 
>> It could be interpret that this is a general statement. I would just interpret that it is not clipped by the 'overflow' property. After all Firefox allows clipping with 'clip-path', so this seems not to be the reason:
>> 
>> CSS 2.0 was more explicit in this regard. http://www.w3.org/TR/1998/REC-CSS2-19980512/visufx.html#clipping I don't know whether the sentence was removed because it was tautologous or wrong though. 
> I see, this is different in CSS 2.1 indeed. CSS 2.1 has less restrictions. Do I understand that both is implemented this way in SVG and HTML for Firefox? I would need to test other browsers as well.
I wrote a test for 'overflow: visible' and 'clip: rect()' to test behavior across all browsers on HTML. The 'clip' property clips if 'overflow' is set to 'visible' (initial value). Here is my test file:

<!DOCTYPE html>
<html lang="en">
<head>
 <meta charset="utf-8">
 <style>
#a {
	width: 200px;
	height: 200px;
	background-color: blue;
	position: absolute;
	overflow: visible;
	clip: rect(0, 200px, 200px, 0);
}
#b {
	width: 500px;
	height: 500px;
	background-color: blue;
}
 </style>
</head>
<body>
<div id="a">
 <div id="b">
 </div>
</div>
</body>
</html>

The result is a blue rect with the size 200x200 pixel. It looks like all browsers (including Firefox) implement 'clip' on HTML according to CSS 2.1.

Greetings,
Dirk


> 
> Greetings,
> Dirk
> 
> 
>> 
>> Best regards
>> 
>> Robert.
>> 
> 
> 
Received on Thursday, 11 October 2012 15:30:58 UTC

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