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Re: [CSSWG] Minutes and Resolutions 2009-02-04: box-shadow and border-image

From: Robert O'Callahan <robert@ocallahan.org>
Date: Fri, 13 Feb 2009 09:22:39 +1300
Message-ID: <11e306600902121222h14cad369j7a4cd3e50444e6a7@mail.gmail.com>
To: Brad Kemper <brad.kemper@gmail.com>
Cc: David Hyatt <hyatt@apple.com>, fantasai <fantasai.lists@inkedblade.net>, "Tab Atkins Jr." <jackalmage@gmail.com>, "www-style@w3.org" <www-style@w3.org>
On Fri, Feb 13, 2009 at 8:43 AM, Brad Kemper <brad.kemper@gmail.com> wrote:

> 1. How to deal with soft image edges, where there is variable opacity?
> Currently, WebKit seems to clip shadows to the vector edge of the border
> box, and not draw them behind areas of variable opacity (such as
> backgrounds). It seems like for a raster image that was 50% opaque, it would
> have draw the shadow behind the whole image at 50% of its normal opacity.


That's the way to go. What you would do is construct a mask the size of the
border-box whose alpha values in the border are the border-image's alpha
values, and whose alpha values in the padding-box are 1. Then you apply blur
to that mask (or not) and draw the shadow color through the mask.


> Or do you set some sort of threshold on images of varying opacity, and just
> draw a hard inner edge at 50% and not draw shadows for any pixels more
> transparent than that? Any of those choices may or may not be what the
> author wants. Setting the shadow in the image himself provides more options.
>

Obviously there will always be cases where the border-image/box-shadow
combination won't produce the exact shadow pixels you want, but you can
still hack those into the border-image; now your argument is restricted to a
much smaller set of desired renderings *and* to users who aren't loading
images *and* who nevertheless care about seeing a shadow.

Using the border-image as the mask is a great idea. I think we should do
that. Fairly easy for us to implement too.

Rob
-- 
"He was pierced for our transgressions, he was crushed for our iniquities;
the punishment that brought us peace was upon him, and by his wounds we are
healed. We all, like sheep, have gone astray, each of us has turned to his
own way; and the LORD has laid on him the iniquity of us all." [Isaiah
53:5-6]
Received on Thursday, 12 February 2009 20:23:16 GMT

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