shadow through transparent background (was Re: Shadow knockout)

On 27/01/2011 3:05 PM, Eric A. Meyer wrote:

> I don't doubt it. I do have to wonder why an outset shadow is clipped by
> the border box, though. Because it is a bit weird to shadow a box, then
> decide to make the background transparent and not see the rest of the
> shadow. Is that an ease-of-implementation thing?

No, some members of the CSS WG in there wisdom decided that a box-shadow 
seen through a transparent background was wrong. I argued against it 
back in 2008 [1]. I suggested it again a few weeks ago [2]. It would 
work like this (the default would be mask).

  box-shadow: 10px 10px 10px 0 <color> cast;

> Or is it that because
> backgrounds are transparent by default, it's thought the shadow
> shouldn't be visible behind the content because that could create
> legibility problems?

Not if it's done carefully. Also a box-shadow does not have to be dark. 
If you offset the box-shadow enough, you can see how the full box-shadow 
is rendered. This means that a full box-shadow is painted first and then 
implementations have to apply a mask on the shadow where it intersects 
the border-box of the background.

1. <>
2. <>


Armies Cannot Stop An Idea Whose Time Has Come. - Victor Hugo

Received on Thursday, 27 January 2011 06:07:30 UTC