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Re: [css3-background] possibly too late for last call, but: background-opacity?

From: Giovanni Campagna <scampa.giovanni@gmail.com>
Date: Mon, 19 Oct 2009 13:39:22 +0200
Message-ID: <65307430910190439u3fd711fbkb0377c6e609f7bcb@mail.gmail.com>
To: robert@ocallahan.org
Cc: www-style@w3.org
2009/10/18 Robert O'Callahan <robert@ocallahan.org>:
> On Mon, Oct 19, 2009 at 1:50 AM, Giovanni Campagna
> <scampa.giovanni@gmail.com> wrote:
>>
>> 2009/10/18 Robert O'Callahan <robert@ocallahan.org>
>>>
>>> Perhaps it's worth taking a step back and asking whether we can deal with
>>> this problem at its root by making it possible for multiple rules to combine
>>> to create a complex value.
>>
>> So what do you propose to address this?
>
> I don't have a specific proposal.

Good, so we can build one up now.

>> 3) Magic syntax allow to specify only part of a value. For example,
>> "background-image: $(image,4)=url(foo.png)" to set only the forth layer of
>> background.
>> Pros: very explicit, little typing, can be used in a variety of contexts
>> Cons: new programming-language-like syntax (especially the type part)
>
> Something like "background-image: image-opacity(_, 0.5);" had popped into my
> head. To say that I have not thought it through would be an understatement.
>
> This is a really tough problem that touches the fundamentals of CSS. However
> I think it'd be better to tackle this problem than to coin lots of new
> properties (and be forced to keep on doing so forever into the future).

Agreed completely, the problem is inventing something which works
reasonably and can be included directly in Cascading & Inheritance 3 /
4, not in every property / module / value.

>>
>>>> 2) You cannot use that for "drop-shadow" (because the drop-shadowed
>>>> border-image would be clipped, making it no better than Photoshop)
>>>
>>> Not sure what you mean here.
>>>
>> One of the problems of using Photoshop for drop-shadowing a border-image
>> is that splicing breaks the shadow. Using CSS to generate an image to splice
>> is no better.
>
> Ah right. Yes, I wasn't proposing to create an image function that adds drop
> shadows. I think 'filter' is much more appropriate for that.

Ok.

>> What if I want to set the opacity for all the content (images and text)?
>> Do I need to go through "color:rgba(0,0,0,0.5)", "element > img { opacity:
>> 0.5; }", "element > .mark { color:rgba(255,0,0,0.5) }"?
>
> OK, I think I see what you mean. I'd use 'filter' for that and add a named
> "CSSContent" filter image.

Uhm... no CSS only solution? I supposed this was a goal when you
designed gradients, for example.

>>
>>
>>>>
>>>> There's an SVG Param spec on the filter side, we only need syntax on the
>>>> CSS side. But I would object to that use of comma, I believe there are
>>>> use-case for multiple filters.
>>>
>>> Yes, there are. It would be even better if CSS could support multiple
>>> rules that each supply a filter to be applied to an element simultaneously.
>>
>> 1) Filters cannot be applied simultaneously, they operate on rendered
>> content (treating it like a static image) so you need to define an order,
>> right?
>
> Right, yes, I meant the CSS rules apply simultaneously, clearly the filters
> have to be applied in some order.

Ok.

>>
>> 2) Do you mean having "filter-blend", "filter-color-matrix",
>> "filter-component-transfer", "filter-composite", "filter-convolve-matrix",
>> "filter-diffuse-lighting", "filter-displacement-map", "filter-flood",
>> "filter-gaussian-blur", "filter-morphology", "filter-offset",
>> "filter-specular-lighting", "filter-tile", "filter-turbulence" as distinct
>> properties, plus additional properties for common effects (like
>> "drop-shadow")? They're a lot!
>
> No. What I mean is that you'd like to be able to do something like
> .a { filter:add url(effects.svg#blur); }
> .b { filter:add url(effects.svg#grayscale); }
> and have <div class="a b"> get both filters applied. (Again, I just made up
> that syntax five seconds ago and I don't claim it makes any sense.)

Ah, sorry I misunderstood.
Then again the problem lives in cascading, not specifically to
filters. There are a lot of properties that would benefit from add().

> 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]
>

Giovanni
Received on Monday, 19 October 2009 11:39:56 GMT

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