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Re: Ambiguities in fill:url() / stroke:url() syntax

From: Robert O'Callahan <robert@ocallahan.org>
Date: Tue, 30 Oct 2012 11:35:42 +1300
Message-ID: <CAOp6jLY3Ra66PKE1DqRbTJ3CpcUAosD2D-94TevPPg5pyEsvnQ@mail.gmail.com>
To: Dirk Schulze <dschulze@adobe.com>
Cc: Karl Dubost <karld@opera.com>, www-svg <www-svg@w3.org>, www-style <www-style@w3.org>
On Tue, Oct 30, 2012 at 10:48 AM, Dirk Schulze <dschulze@adobe.com> wrote:

> He suggests not doing any heuristics, but follow a predefined default
> behavior. 'fill', 'stroke', 'mask', 'clip-path' always assume that
> fragments (which are no media fragments) are treated as resources. For all
> other properties, they are treated as images.
>

This approach seems at least acceptable. I'm not sure that it's optimal. It
does need to be fleshed out a little bit.

For CSS Masking that would mean:
>
>         mask: url(image.svg#id) is assumed to be a mask resource. At least
> if it is the only reference. If it has more than one list item, it is
> treated as image again.
>
>         mask-image: url(image.svg#id) is assumed to be an image, since the
> property, by default, takes CSS Images.
>

This is a problem. I don't think we can, according to the architecture of
CSS, make the interpretation of a CSS property value depend on whether it
came from a shorthand or not. I also think it would be awfully confusing
for authors. And consider the CSSOM implications if you set 'mask' and then
read the computed value of 'mask-image'.

My best idea there would be to make 'mask-image' default to a paint-server.
So the proposal would be:
Given a url() value in the context of a property P:
a) if the URI has no fragment identifier, treat it as an image load.
b) if the URI has a fragment identifier, treat it as an external resource
reference if P is 'mask-image', 'fill', 'stroke', 'clip-path', 'filter'
(... extensible list of SVG CSS properties here), otherwise treat it as an
image load.

This means that background-image etc can only refer to a paint server using
the element() syntax, not the url() syntax; CSS image-value syntax is not
fully unified across properties. This proposal may be more confusing to
authors than my property-independent proposal, I'm not sure. This proposal
is more compatible with SVG stacks. Overall, I'd be happy with either
proposal. Someone please make a decision! :-)

Rob
-- 
Jesus called them together and said, “You know that the rulers of the
Gentiles lord it over them, and their high officials exercise authority
over them. Not so with you. Instead, whoever wants to become great among
you must be your servant, and whoever wants to be first must be your
slave — just
as the Son of Man did not come to be served, but to serve, and to give his
life as a ransom for many.” [Matthew 20:25-28]
Received on Monday, 29 October 2012 22:36:11 GMT

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