W3C home > Mailing lists > Public > www-style@w3.org > May 2013

Re: [css3-background] background-attachment: local

From: Simon Sapin <simon.sapin@exyr.org>
Date: Wed, 29 May 2013 23:58:54 +0800
Message-ID: <51A625BE.60201@exyr.org>
To: fantasai <fantasai.lists@inkedblade.net>
CC: www-style@w3.org
Le 23/05/2013 00:53, fantasai a écrit :
> On 05/22/2013 12:27 PM, fantasai wrote:
>> We were looking implementing 'background-attachment: local' in Gecko, and
>> ran across the following problem in its definition:
>>
>> The goal of 'background-attachment: local' is to allow authors to get
>> the behavior of 'background-attachment: scroll' on the canvas background
>> when setting the background of an element with 'overflow: scroll'. IMHO
>> this should have been the behavior of 'background-attachment: scroll'
>> in the first place, but the WG at the time decided it should behave like
>> 'fixed' on such elements; therefore we added a new keyword, 'local', in
>> level 3.
>>
>> The spec defines this for the background's "attachment", but it doesn't
>> for its positioning. Case to consider: a background image positioned to
>> the bottom right corner. In the case of 'background-attachment: scroll'
>> on the canvas, it is at the bottom of the scrollable area, not the bottom
>> of the viewport. Similarly, 'background-attachment: local' should put
>> such an image at the bottom of the scrollable area, not the bottom of
>> the viewport. However, the spec doesn't specify this, so would need to
>> be amended to fix that.
>
> Here's a diagram:
>
> +------------------------------------+
> |+---------------------------------+A|
> ||                                 | |
> ||                                 | |
> ||                                 | |
> ||                                 | |
> ||                                 | |
> ||                                 | |
> ||                         +------+| |
> ||                         |+++++ || |  <-- bottom right of scrolling box
> ||                         |+image|| |
> ||                         +------+|V|
> +|---------------------------------|-+
>    |                                 |
>    |                                 |
>    |                                 |
>    |                                 |
>    |                                 |
>    |                                 |
>    |                                 |
>    |                                 |
>    |                                 |
>    |                                 |
>    |                         +------+|
>    |                         |+++++ ||
>    |                         |+image||  <-- bottom right of scrolled content
>    |                         +------+|
>    +---------------------------------+

Yes, I think it makes sense for the background positioning area to be in 
sized to the scrolled content, since this is where it is attached.

-- 
Simon Sapin
Received on Wednesday, 29 May 2013 15:59:23 UTC

This archive was generated by hypermail 2.3.1 : Wednesday, 29 May 2013 15:59:23 UTC