Re: [css-images][css-compositing] Blurring an element’s backdrop

On Wed, Nov 27, 2013 at 10:50 AM, Michael Mullany <michael@sencha.com>wrote:

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> On Fri, Nov 22, 2013 at 3:05 PM, Rik Cabanier <cabanier@gmail.com> wrote:
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>> On Thu, Sep 19, 2013 at 10:08 AM, Dean Jackson <dino@apple.com> wrote:
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>>> On 18 Sep 2013, at 1:05 pm, Dirk Schulze <dschulze@adobe.com> wrote:
>>>
>>>
>>> > I suggest adding a new keyword 'backdrop' as CSS Image. This can be
>>> filtered with the CSS Image filter()[3] function and blended with
>>> background colors or background images and the 'background-blend-mode'
>>> property. This would produce results where the backdrop directly behind the
>>> element would always be blurry, but around the element it isn't. This looks
>>> even nicer on scrolling and other interactions.
>>>
>>> I think I suggested a separate property: background-filter (I can’t
>>> remember if I emailed this, or spoke up at a meeting, or just thought of it
>>> in the shower).
>>>
>>> The reason is that I think in most cases you want to draw normally and
>>> just apply the effect to the background. There is no need to consider the
>>> content of the element to be filtered for this effect. However, the name is
>>> a bit misleading because, as you know, it is not filtering the element’s
>>> background (in CSS terms), but its backdrop.
>>>
>>
> I think it's sort of weird that you've removed enable-background from the
> SVG portion Filters because it was hard to implement (although IE does a
> perfectly serviceable job of implementing BackgroundImage per SVG 1.1
> spec.), but now you're proposing to add it again but in a way that means it
> can't participate in an SVG filter chain, but perhaps I misunderstand the
> proposal.
>

The intent was always to reintroduce it, but using the 'isolation' property
[1] instead of the more confusing 'enable-background' property.
I'm unsure why you think that it can't participate in the filter chain. Can
you explain?


>  I've been seeing this effect use more lately. Designers have to create
>> it manually or emulate it with CSS filters and careful overlapping of
>> elements. Maybe it's time to make it a simple CSS property like you propose.
>>
>> All cases I've seen so far, apply the background blur over a rectangular
>> region. Earlier in the thread, I suggested that the effect should only
>> apply to the shape/coverage area but maybe that makes it too hard to
>> implement.
>>
>
> Speaking for Sencha and the types of apps that our community creates, we
> want to be able to duplicate the blend/blur styles introduced by iOS7.
> Which means that a simple blur is not enough - we need finer control of the
> blur opacity/falloff. I did an example of this using SVG filters and
> feImage (no BackgroundImage's were harmed in the making of this demo) It
> uses a feFuncA to tweak the standard Blur behavior.
>
> http://codepen.io/mullany/pen/diolI
>

I agree that just blurring is not enough. Ideally, we would define a syntax
that does something reasonable by default but that you can tweak. For
instance, some examples use screen or soft light blending of the backdrop
and a color (typically white).

We should also say that the blur area is determined by the background-clip
for now [2] and is drawn before background color and images.

1: http://dev.w3.org/fxtf/compositing-1/#isolation
<http://dev.w3.org/fxtf/compositing-1/#isolation>
2: http://www.w3.org/TR/css3-background/#background-clip