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Re: [css3-background] blending on 'box-shadow' and 'text-shadow'

From: Rik Cabanier <cabanier@gmail.com>
Date: Tue, 10 Apr 2012 16:20:32 -0700
Message-ID: <CAGN7qDBUC-QztqSLBcBWMHGtbb1d5KD3SHeWHuZ2vKLxQSRyJg@mail.gmail.com>
To: Simon Fraser <smfr@me.com>
Cc: www-style list <www-style@w3.org>
I agree that this implies that the shadow becomes a separate element for HW
However, once you do so, you can attach a shader to that layer and the
blending will be done on the GPU. It wouldn't matter at that point what is
happening underneath the shadow.

For Safari, you could directly use Core Image (


On Tue, Apr 10, 2012 at 4:01 PM, Simon Fraser <smfr@me.com> wrote:

> On Apr 10, 2012, at 3:52 PM, Rik Cabanier wrote:
> All,
> I'm currently working on the blending specification (
> http://blogs.adobe.com/webplatform/2012/04/04/bringing-blending-to-the-web/)
> and someone brought up that a very common use case for blending is drop
> shadows.
> Some of our applications such as Photoshop, Illustrator and InDesign set
> the shadow to multiply by default since it provides a more pleasing
> appearance that can't be done with simple alpha blending. See
> http://css-tricks.com/dont-use-black-for-shadows/ for a discussion on why
> this is.
> Would there be interest in an additional keyword to specify blending to
> 'box-shadow' or 'text-shadow'?
> the syntax could look like:
> box-shadow: 64px 64px 12px 40px rgba(0,0,0,0.4) multiply
> Using a different blend mode just for the shadow would place a burden on
> implementers who use hardware acceleration of various kinds (i.e. most of
> us now).
> Imagine a box-shadow overlapping a playing video. The implementation has
> to separate the shadow into its own GPU texture, and composite that with a
> different blending mode from the rest of the element, for every frame of
> video.
> Simon
Received on Tuesday, 10 April 2012 23:21:01 UTC

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